Notice2026-07768
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Francis Scott Key Bridge Rebuild Project in Baltimore, Maryland
Primary source
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Published
April 22, 2026
Issuing agencies
Commerce DepartmentNational Oceanic and Atmospheric Administration
Abstract
NMFS has received a request from the Federal Highway Administration (FHWA) for authorization to take marine mammals incidental to the Francis Scott Key (FSK) Bridge Rebuild project in Baltimore, MD. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue two consecutive incidental harassment authorizations (IHAs) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on possible one-time, 1-year renewals that could be issued under certain circumstances and if all requirements are met, as described in Request for Public Comments at the end of this notice. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.
Full Text
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<title>Federal Register, Volume 91 Issue 77 (Wednesday, April 22, 2026)</title>
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[Federal Register Volume 91, Number 77 (Wednesday, April 22, 2026)]
[Notices]
[Pages 21425-21448]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-07768]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[RTID 0648-XF473]
Takes of Marine Mammals Incidental to Specified Activities;
Taking Marine Mammals Incidental to the Francis Scott Key Bridge
Rebuild Project in Baltimore, Maryland
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; proposed incidental harassment authorizations; request
for comments on proposed authorizations and possible renewal.
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SUMMARY: NMFS has received a request from the Federal Highway
Administration (FHWA) for authorization to take marine mammals
incidental to the Francis Scott Key (FSK) Bridge Rebuild project in
Baltimore, MD. Pursuant to the Marine Mammal Protection Act (MMPA),
NMFS is requesting comments on its proposal to issue two consecutive
incidental harassment authorizations (IHAs) to incidentally take marine
mammals during the specified activities. NMFS is also requesting
comments on possible one-time, 1-year renewals that could be issued
under certain circumstances and if all requirements are met, as
described in Request for Public Comments at the end of this notice.
NMFS will consider public comments prior to making any final decision
on the issuance of the requested MMPA authorization and agency
responses will be summarized in the final notice of our decision.
DATES: Comments and information must be received no later than May 22,
2026.
ADDRESSES: Comments should be addressed to Permits and Conservation
Division, Office of Protected Resources, National Marine Fisheries
Service and should be submitted via email to <a href="/cdn-cgi/l/email-protection#c68f9296e88ea9b2a5aeadafa886a8a9a7a7e8a1a9b0"><span class="__cf_email__" data-cfemail="561f0206781e3922353e3d3f38163839373778313920">[email protected]</span></a>.
Electronic copies of the application and supporting documents, as well
as a list of the references cited in this document, may be obtained
online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities</a>. In
case of problems accessing these documents, please call the contact
listed below.
Instructions: NMFS is not responsible for comments sent by any
other method, to any other address or individual, or received after the
end of the comment period. Comments, including all attachments, must
not exceed a 25-megabyte file size. All comments received are a part of
the public record and will generally be posted online at <a href="https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act">https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act</a> without change. All personal identifying
information (e.g., name, address) voluntarily submitted by the
commenter may be publicly accessible. Do not submit confidential
business information or otherwise sensitive or protected information.
FOR FURTHER INFORMATION CONTACT: Cara Hotchkin, Office of Protected
Resources, NMFS, (301) 427-8401.
SUPPLEMENTARY INFORMATION:
Background
The MMPA prohibits the ``take'' of marine mammals, with certain
exceptions. Section 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et
seq.) directs the Secretary of Commerce (as delegated to NMFS) to
allow, upon request, the incidental, but not intentional, taking of
small numbers of marine mammals by U.S. citizens who engage in a
specified activity (other than commercial fishing) within a specified
geographical region if certain findings are made and either regulations
are proposed or, if the taking is limited to harassment, a notice of a
proposed IHA is provided to the public for review.
Authorization for incidental takings shall be granted if NMFS finds
that the taking will have a negligible impact on the species or
stock(s) and will not have an unmitigable adverse impact on the
availability of the species or stock(s) for taking for subsistence uses
(where relevant). Further, NMFS must prescribe the permissible methods
of taking; other ``means of effecting the least practicable adverse
impact'' on the affected species or stocks and their habitat, paying
particular attention to rookeries, mating grounds, and areas of similar
significance, and on the availability of the species or stocks for
taking for certain subsistence uses (referred to as ``mitigation'');
and requirements pertaining to the monitoring and reporting of the
takings. The definitions of all applicable MMPA statutory terms used
above are included in the relevant sections below (see also 16 U.S.C.
1362; 50 CFR 216.3, 216.103).
National Environmental Policy Act
To comply with the National Environmental Policy Act of 1969 (NEPA;
42 U.S.C. 4321 et seq.) and NOAA Administrative Order (NAO) 216-6A,
NMFS must review our proposed action (i.e., the issuance of an IHA)
with respect to potential impacts on the human environment.
This action is consistent with categories of activities identified
in Categorical Exclusion B4 (IHAs with no anticipated serious injury or
mortality) of the Companion Manual for NAO 216-6A, which do not
individually or cumulatively have the potential for significant impacts
on the quality of the human environment and for which we have not
identified any extraordinary circumstances that would preclude this
categorical exclusion. Accordingly, NMFS has preliminarily determined
that the issuance of the proposed IHAs qualifies to be categorically
excluded from further NEPA review.
Summary of Request
On December 9, 2025, NMFS received a request from FHWA for two
consecutive IHAs to take marine mammals incidental to construction
activities necessary for the FSK Bridge Rebuild project in Baltimore,
MD. Following NMFS' review of the application, FHWA submitted revised
versions on January 21, 2026 and March 23, 2026. The application was
deemed adequate and complete on March 26, 2026. FHWA's request is for
take of Tamanend's bottlenose dolphins (Tursiops erebennus) by Level B
harassment only. Neither FHWA nor NMFS expect serious injury or
mortality to result from this activity and, therefore, IHAs are
appropriate.
Description of Proposed Activity
Overview
FHWA proposes to replace a pre-existing critical bridge and
associated infrastructure which were destroyed during a ship collision
in March 2024. The proposed project includes construction of a new
bridge structure
[[Page 21426]]
with two travel lanes in each direction designed to current roadway
standards over the Fort McHenry Navigation Channel, and twelve new
piers in the Patapsco River. Construction activities associated with
the proposed project include vibratory and impact installation of steel
pipe piles ranging from 24-inches (in) (61 centimeters (cm)) to 96-in
(244 cm) in diameter for a temporary construction trestle and main span
piers and associated vessel collision protection systems. Pile driving
activities may be concurrent for up to four piles at a time. Due to the
overall work schedule and accelerated/emergency need for the project,
pile driving would occur year-round.
Dates and Duration
Construction is proposed between June 1, 2026 and May 31, 2028;
thus FHWA has requested two sequential IHAs that would be effective for
June 1, 2026 through May 31, 2027 and for June 1, 2027 through May 31,
2028, respectively. However, project delays may occur due to a number
of factors, including availability of equipment and/or materials,
weather-related delays, equipment maintenance and/or repair, and other
contingencies.
The total project duration would exceed 2 years, including
demolition of remaining elements of the original bridge. If necessary,
FHWA intends to apply for additional incidental harassment
authorizations to cover that period of work.
A total of approximately 728 piles would be installed during Year 1
and a total of 107 piles would be installed during Year 2 (table 1).
Between April 15 and October 30th of each year, work would generally be
limited to daylight construction, typically consisting of a 12 hours on
and 12 hours off work schedule. Pile driving activities would be
initiated only during daylight hours. Concurrent driving of up to four
piles at different locations along the bridge span is proposed. Table 1
shows the number of each type of pile and number of workdays planned
for installation for each season. Seasons are defined as follows:
`summer' is June through August, `fall' is September through November,
`winter' is December through February, and `spring' is March through
May.
Table 1--Estimated Number of Piles and Workdays \a\ During Each Season for Years 1 and 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
24-in 36-in 48-in 96-in Totals
-------------------------------------------------------------------------------------------------------------
# Piles Days # Piles Days # Piles Days # Piles Days # Piles Days
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Summer.................................... 44 31 20 11 0 0 92 117 156 159
Fall...................................... 33 21 139 84 0 0 57 119 229 224
Winter.................................... 29 20 115 67 0 0 65 120 209 207
Spring.................................... 42 23 40 20 16 30 36 69 134 142
-------------------------------------------------------------------------------------------------------------
Total Year 1.......................... 148 95 314 182 16 30 250 425 728 732
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Year 2
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Summer.................................... 13 8 0 0 40 59 0 0 53 67
Fall...................................... 0 0 0 0 34 55 0 0 34 55
Winter.................................... 0 0 0 0 20 20 0 0 20 20
Spring.................................... 0 0 0 0 0 0 0 0 0 0
-------------------------------------------------------------------------------------------------------------
Total Year 2.......................... 13 8 0 0 94 134 0 0 107 142
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\a\ The number of workdays per year exceeds 365 because this calculation excludes concurrent driving. The actual number of workdays in year 1 is 311,
and for year 2 is 142 days.
Specific Geographic Region
The proposed project will occur within portions of Curtis Bay,
Patapsco River, and Bear Creek, near the Port of Baltimore (figure 1).
The Patapsco River is approximately 1.6 kilometers (km; 1 mile) wide
(between Hawkins Point and Sollers Point). United States Army Corps of
Engineers (USACE) maintains the Fort McHenry Navigational Channel,
which is 0.2 km (800 feet (ft)) wide and 15 m (50 ft) deep at the
location of the bridge.
[[Page 21427]]
[GRAPHIC] [TIFF OMITTED] TN22AP26.000
Detailed Description of the Specified Activity
The proposed project includes construction of a new bridge
structure with two travel lanes in each direction designed to current
roadway standards, a minimum vertical clearance of 70.1 m (230 ft) over
the Fort McHenry Navigation Channel, a horizontal clearance of 333.3 m
(1,100 ft), an anticipated main bridge span length of 504.5 m (1,665
ft), and twelve new piers in the Patapsco River. Construction
activities anticipated to occur within years 1 and 2 of the project
include:
<bullet> Vibratory installation of 24-in (61 cm) diameter battered
steel pipe piles; and vibratory and impact installation of 36-in (91
cm) diameter plumb steel pipe piles for a temporary construction
trestle;
<bullet> Vibratory and impact installation of 48-in (1.22 m)
diameter plumb steel pipe piles for marine approach piers (Piers 20,
21, and 28-31); and
<bullet> Vibratory and impact installation of 96-in (2.44 m)
diameter plumb steel pipe piles for main span piers (Piers 22-27) and
associated vessel collision protection systems.
Construction activities that are likely to occur after the
expiration of the proposed authorizations include demolition of
remnants of the original bridge, including existing girders on the six
remaining water spans and removing select in-water piers. Demolition
may be by mechanical demolition to the mudline or by controlled
blasting. Demolition is likely to be conducted after May 31, 2028, and
FHWA intends to apply for additional authorizations as necessary.
Blasting activities are therefore not addressed further in this notice.
On the south side of the navigation channel, construction would
begin with Pier 24 and progress south to the southern shoreline to Pier
20. On the northern side of the navigation channel, construction would
begin at Pier 25 and progress north to the northern shoreline towards
Pier 32. Construction of the temporary trestle will occur as the piers
are constructed. Concurrent pile driving is expected for up to four
piles simultaneously at different locations along the bridge span.
Pile installation would be by vibratory (all sizes) and impact
driving (36-in, 48-in, and 96-in piles). A typical installation
scenario for a 96-in diameter pile begins with vibratory driving for
approximately 5-30 minutes (min) to set each pile and then impact pile
driving to complete pile installation. Impact installation of 96-in
steel piles would occur for approximately 3 hours, with approximately
2,500 strikes per pile. Restriking of certain 96-in piles with an
impact hammer may also occur, with approximately 200 strikes per pile.
Restrikes are not anticipated for piles smaller than 96-in diameter,
and it is expected that impact installation for the 96-in diameter
piles represents the maximum amount of time for impact pile
installation for piles of any size. A similar method of vibratory and
impact pile driving would be used to install the 48-in diameter and 36-
in diameter steel pipe piles. The 24-in diameter piles would require
only vibratory pile driving. Table 2 shows proposed pile quantities and
estimated installation times.
[[Page 21428]]
Table 2--Pile Quantities and Installation Time for Years 1 and 2
----------------------------------------------------------------------------------------------------------------
Approx. time
Year Pile diameter Approx. number Method (vibratory/ Approx. total Maximum piles
(in) of piles impact) \a\ days \b\ per day
----------------------------------------------------------------------------------------------------------------
1......... 96 250 Vibratory and 5-30 min/3 hours. 425 6
Impact.
48 16 30 6
36 314 182 8
24 148 Vibratory........ 30 min........... 95 2
2......... 24 13 Vibratory........ 30 min........... 8 2
48 94 Vibratory and 5- 30 min/3 hours 134 6
Impact.
----------------------------------------------------------------------------------------------------------------
\a\ Estimates 2,500 strikes per pile for impact installation and 5-30 minutes of vibratory per pile for
vibratory installation. Estimated number of strikes per pile based on installation of 96'' diameter piles.
Smaller piles are estimated to require less strikes per pile.
\b\ Some workdays will occur concurrently.
During Year 1 (June 1, 2026 through May 31, 2027), pile
installation would include approximately 250 96-in diameter steel pipe
piles for main span (Piers 22-27) as well as the associated vessel
collision pier protection systems for these piers. 96-in diameter piles
would primarily be installed during Year 1, with the goal of being
completed in the May 2027 timeframe. In addition, approximately 16 48-
in diameter steel pipe piles would be installed for the marine approach
piers (Piers 20-21 on the south side of the river and Piers 28-31 on
the north side of the river). Approximately 314 36-in and 148 24-in
diameter steel pipe piles would be driven for the temporary
construction trestle. A total of approximately 728 piles will be
installed during Year 1 (Table 1).
Installation of 96-in diameter piles at the main span piers during
Year 1 may occur concurrently or may be concurrent with each other and
with vibratory and impact installation of 36-in piles and vibratory
installation of 24-in piles for the construction trestle. At any time,
the distance between concurrent installation of 96-in piles would be
greater than 445 m (0.28 mi). Table 3 provides a summary of possible
concurrent pile driving scenarios.
Table 3--Potential Concurrent Driving Scenarios
------------------------------------------------------------------------
Equipment and
Structure Activity quantity
------------------------------------------------------------------------
Pier............................ Pier 24/25 Pier:
installation of <bullet> 2
two 96-in piles. vibratory
hammers.
Pier and Trestle................ Pier 24/25 Pier:
installation (96- <bullet> 1 Impact
in pile) and hammer.
trestle <bullet> 1
installation (24- vibratory hammer
in pile). Trestle:
<bullet> 1
vibratory hammer.
Pier and Trestle................ Pier 24/25 Pier:
installation (96- <bullet> 1 Impact
in pile) and hammer.
trestle <bullet> 1
installation (36- vibratory hammer.
in pile). Trestle:
<bullet> 1 impact
hammer.
<bullet> 1
vibratory hammer.
------------------------------------------------------------------------
During Year 2 (June 1, 2027 through May 31, 2028), construction
would focus on completing installation of the marine approach piers
(Piers 20-21 and 28-31) as well as completion of the temporary
construction trestle. Approximately 94 48-in diameter piles would be
installed using impact and vibratory installation. For the temporary
construction trestle, approximately 13 24-in diameter battered piles
would be installed using vibratory installation. Approximately 107
piles in total will be installed during Year 2 (Table 1).
Proposed mitigation, monitoring, and reporting measures are
described in detail later in this document (please see Proposed
Mitigation and Proposed Monitoring and Reporting).
Description of Marine Mammals in the Area of Specified Activities
Sections 3 and 4 of the application summarize available information
regarding status and trends, distribution and habitat preferences, and
behavior and life history of the potentially affected species. NMFS
fully considered all of this information, and we refer the reader to
these descriptions, instead of reprinting the information. Additional
information regarding population trends and threats may be found in
NMFS' Stock Assessment Reports (SARs; <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>) and
more general information about these species (e.g., physical and
behavioral descriptions) may be found on NMFS' website (<a href="https://www.fisheries.noaa.gov/find-species">https://www.fisheries.noaa.gov/find-species</a>).
Table 4 lists all species or stocks for which take is expected and
proposed to be authorized for this activity and summarizes information
related to the population or stock, including regulatory status under
the MMPA and Endangered Species Act (ESA) and potential biological
removal (PBR), where known. PBR is defined by the MMPA as the maximum
number of animals, not including natural mortalities, that may be
removed from a marine mammal stock while allowing that stock to reach
or maintain its optimum sustainable population (as described in NMFS'
SARs). While no serious injury or mortality is anticipated or proposed
to be authorized here, PBR and annual mortality and serious injury (M/
SI) from anthropogenic sources are included here as gross indicators of
the
[[Page 21429]]
status of the species or stocks and other threats.
Marine mammal abundance estimates presented in this document
represent the total number of individuals that make up a given stock or
the total number estimated within a particular study or survey area.
NMFS' stock abundance estimates for most species represent the total
estimate of individuals within the geographic area, if known, that
comprises that stock. For some species, this geographic area may extend
beyond U.S. waters. All managed stocks in this region are assessed in
NMFS' U.S. Atlantic SARs. All values presented in table 4 are the most
recent available at the time of publication (including from the draft
2024 SARs) and are available online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments</a>.
Table 4--Species,\1\ Stocks, and the Status of Marine Mammals With Estimated Take From the Specified Activities
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stock abundance Nbest,
ESA/ MMPA status; (CV, Nmin, most recent Annual M/
Common name Scientific name Stock strategic (Y/N) abundance survey) \3\ PBR SI \3\
\2\
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Order Odontoceti (toothed whales, dolphins, and porpoises)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Family Delphinidae:
Bottlenose Dolphin \4\.......... Tursiops erebennus..... Northern Migratory -, D, Y 6,639 (0.41, 4,759, 48 12.2-21.5
Coastal. 2016).
Southern Migratory -, D, Y 3,751 (0.6, 2,353, 24 0-18.3
Coastal. 2016).
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\1\ Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy
(<a href="https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/">https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/</a>).
\2\ Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed
under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality
exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed
under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
\3\ NMFS marine mammal stock assessment reports online at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region</a>. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance.
\4\ Coastal bottlenose dolphins along the Eastern U.S. have been genetically identified as a separate species (Tamanend's bottlenose dolphin (T.
erebennus)) (Costa et al. 2022); however, this is not yet reflected in the SARs. Here we present the most recent SAR for the two relevant stocks, both
of which are now considered T. erebennus.
As indicated above, only bottlenose dolphins temporally and
spatially co-occur with the activity to the degree that take is
reasonably likely to occur. While fin whales (Balaenoptera physalus),
minke whales (Balaenoptera acutorostrata), humpback whales (Megaptera
novaeangliae), sei whales (Balaenoptera borealis), harbor porpoise
(Phocoena phocoena), and harbor (Phoca vitulina) and grey seals
(Halichoerus grypus) have been documented in Lower Chesapeake Bay or
the waters of coastal Maryland, the temporal and/or spatial occurrence
of these species is such that take is not expected to occur, and they
are not discussed further beyond the explanation provided here. All of
these species are considered extralimital in the waters of the upper
bay and the Patapsco River. Additionally, single individuals of Risso's
dolphin (Grampus griseus) have been found stranded in the Baltimore
area; however, these species are also considered extralimital.
Bottlenose dolphins are the only marine mammal species that are
expected to occur on a regular basis in the waters of the upper
Chesapeake Bay and Patapsco River. Atlantic coastal bottlenose dolphins
have recently been recategorized as Tamanend's bottlenose dolphins
(Tursiops erebennus) by Costa et al. (2022). Tamanend's bottlenose
dolphins within the area of the FSK Bridge project likely belong to
either the Western North Atlantic Northern Migratory Coastal Stock
(NMCS) or the Western North Atlantic Southern Migratory Coastal Stock
(SMCS). The best available abundance estimate for the NMCS is 6,639
(Hayes et al., 2024; Garrison et al., 2017), and for the SMCS is 3,751
(Garrison et al., 2017).
Tamanend's bottlenose dolphins are seasonally transient in the
lower Patapsco River (Rodriguez et al., 2021). They have a higher
likelihood of occurrence along the middle and lower Chesapeake Bay,
outside the area of the project area. Tamanend's bottlenose dolphins
primarily use the lower Chesapeake Bay in summer with most usage near
the James and Elizabeth Rivers in Virginia. They are seen annually in
Virginia from April through November with approximately 65 strandings
occurring each year (Barco and Swingle, 2014; Engelhaupt et al., 2016).
Dolphins are more commonly sighted in areas far south of Baltimore
Harbor including the mouths of the Potomac and Rappahannock Rivers (Bay
Journal, 2021).
Sighting data within the proximity of the project area near the
mouth of the Patapsco River and within the entire Chesapeake Bay, are
based on `citizen science', where reports are logged via the Dolphin
Watch app (<a href="https://chesapeakedolphinwatch.org">https://chesapeakedolphinwatch.org</a>) supported by University
of Maryland, Center for Environmental Science. These data are available
from 2017 through 2022. Logged sightings are less frequent farther
north in the Patapsco River and Baltimore Harbor areas and typically
occur in the summer. Recent reported observations near the immediate
area of the project include a dolphin sighted using waters in the Inner
Harbor (14.5 km (9 miles) north of the Key Bridge; ABC Baltimore 2023)
and a dolphin sighted using waters at the mouth of the Patapsco River
(approximately 8 km (5 miles) south of the Key Bridge; The Washington
Post, 2018).
Rodriguez et al. (2021) synthesizes three consecutive years (2017,
2018, and 2019) of data from the DolphinWatch app. Overall, the highest
dolphin sightings are correlated with water temperatures between 24 and
30 degrees Celsius (75.2 to 86 degrees Fahrenheit). Salinity and tidal
state also influence the spatiotemporal patterns of bottlenose
dolphins. Dolphins were sighted most in the summer. The highest number
of documented dolphin sightings from these data was in July of each
year, when water temperatures are high and provide nursery habitat for
dolphin prey fish species (Gannon and Waples, 2004). During September
and October, dolphins were primarily sighted in the lower and southern
middle portions of the Chesapeake Bay while during the summer, dolphins
occurred in the upper, middle, and lower portions of the bay. No
dolphins were sighted in the upper bay during September and October of
2018.
[[Page 21430]]
Considering data synthesized in this report and global sea temperature
data for the Upper Chesapeake Bay, it is expected that bottlenose
dolphins would most likely be present within the vicinity of the FSK
Bridge Rebuild project between June 1 and September 30 of any given
year. Reduced presence is possible in spring and fall when water
temperatures are above 20 degrees Celsius, and no dolphins are expected
to be present in the project location during winter months.
Marine Mammal Hearing
Hearing is the most important sensory modality for marine mammals
underwater, and exposure to anthropogenic sound can have deleterious
effects. To appropriately assess the potential effects of exposure to
sound, it is necessary to understand the frequency ranges marine
mammals are able to hear. Not all marine mammal species have equal
hearing capabilities (e.g., Richardson et al., 1995; Wartzok and
Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al.
(2007; 2019) recommended that marine mammals be divided into hearing
groups based on directly measured (behavioral or auditory evoked
potential techniques) or estimated hearing ranges (behavioral response
data, anatomical modeling, etc.). Generalized hearing ranges were
chosen based on the approximately 65 decibel (dB) threshold from
composite audiograms, previous analyses in NMFS (2018), and/or data
from Southall et al. (2007) and Southall et al. (2019). We note that
the names of two hearing groups and the generalized hearing ranges of
all marine mammal hearing groups have been recently updated (NMFS,
2024) as reflected below in table 5. Tamanend's bottlenose dolphins are
considered high-frequency (HF) cetaceans.
Table 5--Marine Mammal Hearing Groups
[NMFS, 2024]
------------------------------------------------------------------------
Hearing group Generalized hearing range *
------------------------------------------------------------------------
Low-frequency (LF) cetaceans (baleen 7 Hz to 36 kHz.
whales).
High-frequency (HF) cetaceans 150 Hz to 160 kHz.
(dolphins, toothed whales, beaked
whales, bottlenose whales).
Very High-frequency (VHF) cetaceans 200 Hz to 165 kHz.
(true porpoises, Kogia, river
dolphins, Cephalorhynchid,
Lagenorhynchus cruciger & L.
australis).
Phocid pinnipeds (PW) (underwater) 40 Hz to 90 kHz.
(true seals).
Otariid pinnipeds (OW) (underwater) 60 Hz to 68 kHz.
(sea lions and fur seals).
------------------------------------------------------------------------
* Represents the generalized hearing range for the entire group as a
composite (i.e., all species within the group), where individual
species' hearing ranges may not be as broad. Generalized hearing range
chosen based on approximately 65 dB threshold from composite
audiogram, previous analysis in NMFS (2018), and/or data from Southall
et al. (2007) and Southall et al. (2019). Additionally, animals are
able to detect very loud sounds above and below that ``generalized''
hearing range.
For more detail concerning these groups and associated frequency
ranges, please see NMFS (2024) for a review of available information.
Potential Effects of Specified Activities on Marine Mammals and Their
Habitat
This section provides a discussion of the ways in which components
of the specified activity may impact marine mammals and their habitat.
The Estimated Take of Marine Mammals section later in this document
includes a quantitative analysis of the number of individuals that are
expected to be taken by this activity. The Negligible Impact Analysis
and Determination section considers the content of this section, the
Estimated Take of Marine Mammals section, and the Proposed Mitigation
section, to draw conclusions regarding the likely impacts of these
activities on the reproductive success or survivorship of individuals
and whether those impacts are reasonably expected to, or reasonably
likely to, adversely affect the species or stock through effects on
annual rates of recruitment or survival.
Acoustic effects on marine mammals during the specified activity
are expected to potentially occur from vibratory and impact pile
driving. The effects of underwater noise from FHWA's proposed
activities have the potential to result in Level B harassment of marine
mammals in the action area.
The proposed activities would result in the placement of 728 steel
pipe piles with diameters of 24-, 36-, 48-, and 96-in in year 1 and 107
24- and 48-in diameter steel pipe piles in year 2 (see table 2 for
details). There are a variety of types and degrees of effects on marine
mammals, prey species, and habitat that could occur as a result of the
project. Below we provide a brief description of the types of sound
sources that would be generated by the project, the general impacts
from these types of activities, and an analysis of the anticipated
impacts on marine mammals from the project, with consideration of the
proposed mitigation measures.
Description of Sound Sources for the Specified Activities
Activities associated with the project that have the potential to
incidentally take marine mammals though exposure to sound would include
vibratory and impact pile driving during the construction of the new
bridge.
Impact hammers typically operate by repeatedly dropping and/or
pushing a heavy piston onto a pile to drive the pile into the
substrate. Sound generated by impact hammers is impulsive,
characterized by rapid rise times and high peak levels, a potentially
injurious combination (Hastings and Popper, 2005). Vibratory hammers
install piles by vibrating them and allowing the weight of the hammer
to push them into the substrate. Vibratory hammers typically produce
less sound (i.e., lower levels) than impact hammers. Peak sound
pressure levels (SPLs) may be 180 dB or greater, but are generally 10
to 20 dB lower than SPLs generated during impact pile driving of the
same-sized pile (Oestman et al., 2009; California Department of
Transportation (CALTRANS), 2015, 2020). Sounds produced by vibratory
hammers are non-impulsive; compared to sounds produced by impact
hammers, the rise time is slower, reducing the probability and severity
of injury, and the sound energy is distributed over a greater amount of
time (Nedwell and Edwards, 2002; Carlson et al., 2005).
The likely or possible impacts of the FHWA's proposed activities on
marine mammals could involve both non-acoustic and acoustic stressors.
Potential non-acoustic stressors could result from the physical
presence of the equipment and personnel; however, visual and other non-
acoustic stressors would be limited, and any impacts to marine mammals
are expected to primarily be acoustic in nature.
[[Page 21431]]
Potential Effects of Underwater Sound on Marine Mammals
The introduction of anthropogenic noise into the aquatic
environment from impact and vibratory pile driving is the primary means
by which marine mammals may be harassed from the FHWA's specified
activity. Anthropogenic sounds cover a broad range of frequencies and
sound levels and can have a range of highly variable impacts on marine
life from none or minor to potentially severe responses depending on
received levels, duration of exposure, behavioral context, and various
other factors. Broadly, underwater sound from active acoustic sources,
such as those in the project, can potentially result in one or more of
the following: temporary or permanent hearing impairment, non-auditory
physical or physiological effects, behavioral disturbance, stress, and
masking (Richardson et al., 1995; Gordon et al., 2003; Nowacek et al.,
2007; Southall et al., 2007; G[ouml]tz et al., 2009).
We describe the more severe effects of certain non-auditory
physical or physiological effects only briefly as we do not expect that
use of impact driving is reasonably likely to result in such effects
(see below for further discussion). Potential effects from impulsive
sound sources can range in severity from effects such as behavioral
disturbance or tactile perception to physical discomfort, slight injury
of the internal organs and the auditory system, or mortality (Yelverton
et al., 1973). Non-auditory physiological effects or injuries that
theoretically might occur in marine mammals exposed to high level
underwater sound or as a secondary effect of extreme behavioral
reactions (e.g., change in dive profile as a result of an avoidance
reaction) caused by exposure to sound include neurological effects,
bubble formation, resonance effects, and other types of organ or tissue
damage (Cox et al., 2006; Southall et al., 2007; Zimmer and Tyack,
2007; Tal et al., 2015). The project activities considered here do not
involve the use of devices such as explosives or mid-frequency tactical
sonar that are associated with these types of effects.
In general, animals exposed to natural or anthropogenic sound may
experience physical and psychological effects, ranging in magnitude
from none to severe (Southall et al., 2007, 2019). Exposure to
anthropogenic noise has the potential to result in auditory threshold
shifts and behavioral reactions (e.g., avoidance, temporary cessation
of foraging and vocalizing, changes in dive behavior). It can also lead
to non-observable physiological responses, such an increase in stress
hormones. Additional noise in a marine mammal's habitat can mask
acoustic cues used by marine mammals to carry out daily functions, such
as communication and predator and prey detection.
The degree of effect of an acoustic exposure on marine mammals is
dependent on several factors, including, but not limited to, sound type
(e.g., impulsive vs. non-impulsive), signal characteristics, the
species, age and sex class (e.g., adult male vs. mom with calf),
duration of exposure, the distance between the noise source and the
animal, received levels, behavioral state at time of exposure, and
previous history with exposure (Wartzok et al., 2004; Southall et al.,
2007). In general, sudden, high-intensity sounds can cause hearing loss
as can longer exposures to lower-intensity sounds. Moreover, any
temporary or permanent loss of hearing, if it occurs at all, will occur
almost exclusively for noise within an animal's hearing range. We
describe below the specific manifestations of acoustic effects that may
occur based on the activities proposed by FHWA.
Richardson et al. (1995) described zones of increasing intensity of
effect that might be expected to occur in relation to distance from a
source and assuming that the signal is within an animal's hearing
range. First (at the greatest distance) is the area within which the
acoustic signal would be audible (potentially perceived) to the animal
but not strong enough to elicit any overt behavioral or physiological
response. The next zone (closer to the receiving animal) corresponds
with the area where the signal is audible to the animal and of
sufficient intensity to elicit behavioral or physiological
responsiveness. The third is a zone within which, for signals of high
intensity, the received level is sufficient to potentially cause
discomfort or tissue damage to auditory or other systems. Overlaying
these zones to a certain extent is the area within which masking (i.e.,
when a sound interferes with or masks the ability of an animal to
detect a signal of interest that is above the absolute hearing
threshold) may occur; the masking zone may be highly variable in size.
Below, we provide additional detail regarding potential impacts on
marine mammals and their habitat from noise in general, starting with
hearing impairment, as well as from the specific activities FHWA plans
to conduct, to the degree it is available.
Hearing Threshold Shifts. NMFS defines a noise-induced threshold
shift (TS) as a change, usually an increase, in the threshold of
audibility at a specified frequency or portion of an individual's
hearing range above a previously established reference level (NMFS,
2018, 2024). The amount of threshold shift is customarily expressed in
dB. A TS can be permanent or temporary. As described in NMFS (2018,
2024) there are numerous factors to consider when examining the
consequence of TS, including, but not limited to, the signal temporal
pattern (e.g., impulsive or non-impulsive), likelihood an individual
would be exposed for a long enough duration or to a high enough level
to induce a TS, the magnitude of the TS, time to recovery (seconds to
minutes or hours to days), the frequency range of the exposure (i.e.,
spectral content), the hearing frequency range of the exposed species
relative to the signal's frequency spectrum (i.e., how animal uses
sound within the frequency band of the signal; e.g., Kastelein et al.,
2014), and the overlap between the animal and the source (e.g.,
spatial, temporal, and spectral).
Auditory Injury (AUD INJ). NMFS (2024) defines AUD INJ as damage to
the inner ear that can result in destruction of tissue, such as the
loss of cochlear neuron synapses or auditory neuropathy (Houser 2021;
Finneran 2024). AUD INJ may or may not result in a permanent threshold
shift (PTS). PTS is subsequently defined as a permanent, irreversible
increase in the threshold of audibility at a specified frequency or
portion of an individual's hearing range above a previously established
reference level (NMFS, 2024). PTS does not generally affect more than a
limited frequency range, and an animal that has incurred PTS has some
level of hearing loss at the relevant frequencies; typically animals
with PTS or other AUD INJ are not functionally deaf (Au and Hastings,
2008; Finneran, 2016). Available data from humans and other terrestrial
mammals indicate that a 40-dB threshold shift approximates AUD INJ
onset (see Ward et al., 1958, 1959; Ward, 1960; Kryter et al., 1966;
Miller, 1974; Ahroon et al., 1996; Henderson et al., 2008). AUD INJ
levels for marine mammals are estimates, as with the exception of a
single study unintentionally inducing PTS in a harbor seal (Phoca
vitulina) (Kastak et al., 2008), there are no empirical data measuring
AUD INJ in marine mammals largely due to the fact that, for various
ethical reasons, experiments involving anthropogenic noise exposure at
levels inducing AUD INJ are not typically pursued or authorized (NMFS,
2024).
Temporary Threshold Shift (TTS). TTS is a temporary, reversible
increase in the threshold of audibility at a
[[Page 21432]]
specified frequency or portion of an individual's hearing range above a
previously established reference level (NMFS, 2024), and is not
considered an AUD INJ. Based on data from marine mammal TTS
measurements (see Southall et al., 2007, 2019), a TTS of 6 dB is
considered the minimum threshold shift clearly larger than any day-to-
day or session-to-session variation in a subject's normal hearing
ability (Finneran et al., 2000, 2002; Schlundt et al., 2000). As
described in Finneran (2015), marine mammal studies have shown the
amount of TTS increases with the 24-hour cumulative sound exposure
level (SEL<INF>24</INF>) in an accelerating fashion: at low exposures
with lower SEL<INF>24</INF>, the amount of TTS is typically small and
the growth curves have shallow slopes. At exposures with higher
SEL<INF>24</INF>, the growth curves become steeper and approach linear
relationships with the sound exposure level (SEL).
Depending on the degree (elevation of threshold in dB), duration
(i.e., recovery time), and frequency range of TTS, and the context in
which it is experienced, TTS can have effects on marine mammals ranging
from discountable to more impactful (similar to those discussed in
auditory masking, below). For example, a marine mammal may be able to
readily compensate for a brief, relatively small amount of TTS in a
non-critical frequency range that takes place during a time when the
animal is traveling through the open ocean, where ambient noise is
lower and there are not as many competing sounds present.
Alternatively, a larger amount and longer duration of TTS sustained
during time when communication is critical for successful mother/calf
interactions could have more severe impacts. We note that reduced
hearing sensitivity as a simple function of aging has been observed in
marine mammals, as well as humans and other taxa (Southall et al.,
2007), so we can infer that strategies exist for coping with this
condition to some degree, though likely not without cost.
Many studies have examined noise-induced hearing loss in marine
mammals (see Finneran (2015) and Southall et al. (2019) for summaries).
TTS is the mildest form of hearing impairment that can occur during
exposure to sound (Kryter, 2013). While experiencing TTS, the hearing
threshold rises, and a sound must be at a higher level in order to be
heard. In terrestrial and marine mammals, TTS can last from minutes or
hours to days (in cases of strong TTS) (Finneran, 2015). In many cases,
hearing sensitivity recovers rapidly after exposure to the sound ends.
For cetaceans, published data on the onset of TTS are limited to
captive bottlenose dolphin, beluga whale (Delphinapterus leucas),
harbor porpoise, and Yangtze finless porpoise (Neophocoena
asiaeorientalis) (Southall et al., 2019). For pinnipeds in water,
measurements of TTS are limited to harbor seals, elephant seals
(Mirounga angustirostris), bearded seals (Erignathus barbatus) and
California sea lions (Zalophus californianus) (Kastak et al., 1999,
2007; Kastelein et al., 2019b, 2019c, 2021, 2022a, 2022b; Reichmuth et
al., 2019; Sills et al., 2020). TTS was not observed in spotted (Phoca
largha) and ringed (Pusa hispida) seals exposed to single airgun
impulse sounds at levels matching previous predictions of TTS onset
(Reichmuth et al., 2016). These studies examine hearing thresholds
measured in marine mammals before and after exposure to intense or
long-duration sound exposures. The difference between the pre-exposure
and post-exposure thresholds can be used to determine the amount of
threshold shift at various post-exposure times.
The amount and onset of TTS depends on the exposure frequency.
Sounds below the region of best sensitivity for a species or hearing
group are less hazardous than those near the region of best sensitivity
(Finneran and Schlundt, 2013). At low frequencies, onset-TTS exposure
levels are higher compared to those in the region of best sensitivity
(i.e., a low frequency noise would need to be louder to cause TTS onset
when TTS exposure level is higher), as shown for harbor porpoises and
harbor seals (Kastelein et al., 2019a, 2019c). Note that in general,
harbor seals and harbor porpoises have a lower TTS onset than other
measured pinniped or cetacean species (Finneran, 2015). In addition,
TTS can accumulate across multiple exposures, but the resulting TTS
will be less than the TTS from a single, continuous exposure with the
same SEL (Mooney et al., 2009; Finneran et al., 2010; Kastelein et al.,
2014, 2015). This means that TTS predictions based on the total
SEL<INF>24</INF> will overestimate the amount of TTS from intermittent
exposures, such as sonars and impulsive sources. Nachtigall et al.
(2018) describe measurements of hearing sensitivity of multiple
odontocete species (bottlenose dolphin, harbor porpoise, beluga, and
false killer whale (Pseudorca crassidens)) when a relatively loud sound
was preceded by a warning sound. These captive animals were shown to
reduce hearing sensitivity when warned of an impending intense sound.
Based on these experimental observations of captive animals, the
authors suggest that wild animals may dampen their hearing during
prolonged exposures or if conditioned to anticipate intense sounds.
Another study showed that echolocating animals (including odontocetes)
might have anatomical specializations that might allow for conditioned
hearing reduction and filtering of low-frequency ambient noise,
including increased stiffness and control of middle ear structures and
placement of inner ear structures (Ketten et al., 2021). Data available
on noise-induced hearing loss for mysticetes are currently lacking
(NMFS, 2024). Additionally, the existing marine mammal TTS data come
from a limited number of individuals within these species.
Relationships between TTS and AUD INJ thresholds have not been
studied in marine mammals, and there are no measured PTS data for
cetaceans, but such relationships are assumed to be similar to those in
humans and other terrestrial mammals. AUD INJ typically occurs at
exposure levels at least several dB above that inducing mild TTS (e.g.,
a 40-dB threshold shift approximates AUD INJ onset (Kryter et al.,
1966; Miller, 1974), while a 6-dB threshold shift approximates TTS
onset (Southall et al., 2007, 2019). Based on data from terrestrial
mammals, a precautionary assumption is that the AUD INJ thresholds for
impulsive sounds (such as impact pile driving pulses as received close
to the source) are at least 6 dB higher than the TTS threshold on a
peak-pressure basis and AUD INJ cumulative sound exposure level
thresholds are 15 to 20 dB higher than TTS cumulative sound exposure
level thresholds (Southall et al., 2007, 2019). Given the higher level
of sound or longer exposure duration necessary to cause AUD INJ as
compared with TTS, it is considerably less likely that AUD INJ could
occur.
Behavioral Effects. Exposure to noise also has the potential to
behaviorally disturb marine mammals to a level that rises to the
definition of harassment under the MMPA. Generally speaking, NMFS
considers a behavioral disturbance that rises to the level of
harassment under the MMPA a non-minor response--in other words, not
every response qualifies as behavioral disturbance, and for responses
that do, those of a higher level, or accrued across a longer duration,
have the potential to affect foraging, reproduction, or survival.
Behavioral disturbance may include a variety of effects, including
subtle changes in behavior (e.g., minor or brief avoidance of an area
or changes
[[Page 21433]]
in vocalizations), more conspicuous changes in similar behavioral
activities, and more sustained and/or potentially severe reactions,
such as displacement from or abandonment of high-quality habitat.
Behavioral responses may include changing durations of surfacing and
dives, changing direction and/or speed; reducing/increasing vocal
activities; changing/cessation of certain behavioral activities (such
as socializing or feeding); eliciting a visible startle response or
aggressive behavior (such as tail/fin slapping or jaw clapping); and
avoidance of areas where sound sources are located. In addition,
pinnipeds may increase their haul out time, possibly to avoid in-water
disturbance (Thorson and Reyff, 2006).
Behavioral responses to sound are highly variable and context-
specific and any reactions depend on numerous intrinsic and extrinsic
factors (e.g., species, state of maturity, experience, current
activity, reproductive state, auditory sensitivity, time of day), as
well as the interplay between factors (e.g., Richardson et al., 1995;
Wartzok et al., 2004; Southall et al., 2007, 2019; Weilgart, 2007;
Archer et al., 2010). Behavioral reactions can vary not only among
individuals but also within an individual, depending on previous
experience with a sound source, context, and numerous other factors
(Ellison et al., 2012), and can vary depending on characteristics
associated with the sound source (e.g., whether it is moving or
stationary, number of sources, distance from the source). In general,
pinnipeds seem more tolerant of, or at least habituate more quickly to,
potentially disturbing underwater sound than do cetaceans, and
generally seem to be less responsive to exposure to industrial sound
than most cetaceans. Please see Appendices B and C of Southall et al.
(2007) and Gomez et al. (2016) for reviews of studies involving marine
mammal behavioral responses to sound.
Habituation can occur when an animal's response to a stimulus wanes
with repeated exposure, usually in the absence of unpleasant associated
events (Wartzok et al., 2004). Animals are most likely to habituate to
sounds that are predictable and unvarying. It is important to note that
habituation is appropriately considered as a ``progressive reduction in
response to stimuli that are perceived as neither aversive nor
beneficial,'' rather than as, more generally, moderation in response to
human disturbance (Bejder et al., 2009). The opposite process is
sensitization, when an unpleasant experience leads to subsequent
responses, often in the form of avoidance, at a lower level of
exposure.
As noted above, behavioral state may affect the type of response.
For example, animals that are resting may show greater behavioral
change in response to disturbing sound levels than animals that are
highly motivated to remain in an area for feeding (Richardson et al.,
1995; Wartzok et al., 2004; National Research Council (NRC), 2005).
Controlled experiments with captive marine mammals have shown
pronounced behavioral reactions, including avoidance of loud sound
sources (Ridgway et al., 1997; Finneran et al., 2003). Observed
responses of wild marine mammals to loud pulsed sound sources (e.g.,
seismic airguns) have been varied but often consist of avoidance
behavior or other behavioral changes (Richardson et al., 1995; Morton
and Symonds, 2002; Nowacek et al., 2007).
Available studies show wide variation in response to underwater
sound; therefore, it is difficult to predict specifically how any given
sound in a particular instance might affect marine mammals perceiving
the signal (e.g., Erbe et al., 2019). If a marine mammal does react
briefly to an underwater sound by changing its behavior or moving a
small distance, the impacts of the change are unlikely to be
significant to the individual, let alone the stock or population. If a
sound source displaces marine mammals from an important feeding or
breeding area for a prolonged period, impacts on individuals and
populations could be significant (e.g., Lusseau and Bejder, 2007;
Weilgart, 2007; NRC, 2005). However, there are broad categories of
potential response, which we describe in greater detail here, that
include alteration of dive behavior, alteration of foraging behavior,
effects to breathing, interference with or alteration of vocalization,
avoidance, and flight.
Avoidance and displacement. Changes in dive behavior can vary
widely and may consist of increased or decreased dive times and surface
intervals as well as changes in the rates of ascent and descent during
a dive (e.g., Frankel and Clark, 2000; Costa et al., 2003; Ng and
Leung, 2003; Nowacek et al., 2004; Goldbogen et al., 2013a, 2013b;
Blair et al., 2016). Variations in dive behavior may reflect
interruptions in biologically significant activities (e.g., foraging)
or they may be of little biological significance. The impact of an
alteration to dive behavior resulting from an acoustic exposure depends
on what the animal is doing at the time of the exposure and the type
and magnitude of the response.
Disruption of feeding behavior can be difficult to correlate with
anthropogenic sound exposure, so it is usually inferred by observed
displacement from known foraging areas, the appearance of secondary
indicators (e.g., bubble nets or sediment plumes), or changes in dive
behavior. Acoustic and movement bio-logging tools also have been used
in some cases to infer responses to anthropogenic noise. For example,
Blair et al. (2015) reported significant effects on humpback whale
(Megaptera novaeangliae) foraging behavior in Stellwagen Bank in
response to ship noise including slower descent rates, and fewer side-
rolling events per dive with increasing ship nose. In addition,
Wisniewska et al. (2018) reported that tagged harbor porpoises
demonstrated fewer prey capture attempts when encountering occasional
high-noise levels resulting from vessel noise as well as more vigorous
fluking, interrupted foraging, and cessation of echolocation signals
observed in response to some high-noise vessel passes. As for other
types of behavioral response, the frequency, duration, and temporal
pattern of signal presentation, as well as differences in species
sensitivity, are likely contributing factors to differences in response
in any given circumstance (e.g., Croll et al., 2001; Nowacek et al.,
2004; Madsen et al., 2006; Yazvenko et al., 2007). A determination of
whether foraging disruptions incur fitness consequences would require
information on or estimates of the energetic requirements of the
affected individuals and the relationship between prey availability,
foraging effort and success, and the life history stage of the animal.
Respiration rates vary naturally with different behaviors and
alterations to breathing rate as a function of acoustic exposure can be
expected to co-occur with other behavioral reactions, such as a flight
response or an alteration in diving. However, respiration rates in and
of themselves may be representative of annoyance or an acute stress
response. Various studies have shown that respiration rates may either
be unaffected or could increase, depending on the species and signal
characteristics, again highlighting the importance in understanding
species differences in the tolerance of underwater noise when
determining the potential for impacts resulting from anthropogenic
sound exposure (e.g., Kastelein et al., 2001; 2005; 2006; Gailey et
al., 2007). For example, harbor porpoise respiration rates increased in
response to pile driving sounds at and above a received broadband SPL
of 136 dB (zero-peak SPL: 151 dB (referenced to 1 micropascal (re 1
[mu]Pa); SEL of a single
[[Page 21434]]
strike (SEL<INF>ss</INF>): 127 dB re 1 [mu]Pa\2\-s) (Kastelein et al.,
2013).
Avoidance is the displacement of an individual from an area or
migration path as a result of the presence of a sound or other
stressors, and is one of the most obvious manifestations of disturbance
in marine mammals (Richardson et al., 1995). For example, gray whales
(Eschrictius robustus) are known to change direction--deflecting from
customary migratory paths--in order to avoid noise from seismic surveys
(Malme et al., 1984). Harbor porpoises, Atlantic white-sided dolphins
(Lagenorhynchus actusus), and minke whales have demonstrated avoidance
in response to vessels during line transect surveys (Palka and Hammond,
2001). In addition, beluga whales in the St. Lawrence Estuary in Canada
have been reported to increase levels of avoidance with increased boat
presence by way of increased dive durations and swim speeds, decreased
surfacing intervals, and by bunching together into groups (Blane and
Jaakson, 1994). Avoidance may be short-term, with animals returning to
the area once the noise has ceased (e.g., Bowles et al., 1994; Goold,
1996; Stone et al., 2000; Morton and Symonds, 2002; Gailey et al.,
2007). Longer-term displacement is possible, however, which may lead to
changes in abundance or distribution patterns of the affected species
in the affected region if habituation to the presence of the sound does
not occur (e.g., Blackwell et al., 2004; Bejder et al., 2006; Teilmann
et al., 2006).
A flight response is a dramatic change in normal movement to a
directed and rapid movement away from the perceived location of a sound
source. The flight response differs from other avoidance responses in
the intensity of the response (e.g., directed movement, rate of
travel). Relatively little information on flight responses of marine
mammals to anthropogenic signals exist, although observations of flight
responses to the presence of predators have occurred (Connor and
Heithaus, 1996; Bowers et al., 2018). The result of a flight response
could range from brief, temporary exertion and displacement from the
area where the signal provokes flight to, in extreme cases, marine
mammal strandings (England et al., 2001). However, it should be noted
that response to a perceived predator does not necessarily invoke
flight (Ford and Reeves, 2008), and whether individuals are solitary or
in groups may influence the response.
Behavioral disturbance can also impact marine mammals in more
subtle ways. Increased vigilance may result in costs related to
diversion of focus and attention (i.e., when a response consists of
increased vigilance, it may come at the cost of decreased attention to
other critical behaviors such as foraging or resting). These effects
have generally not been demonstrated for marine mammals, but studies
involving fishes and terrestrial animals have shown that increased
vigilance may substantially reduce feeding rates (e.g., Beauchamp and
Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In
addition, chronic disturbance can cause population declines through
reduction of fitness (e.g., decline in body condition) and subsequent
reduction in reproductive success, survival, or both (e.g., Harrington
and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However,
Ridgway et al. (2006) reported that increased vigilance in bottlenose
dolphins exposed to sound over a 5-day period did not cause any sleep
deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting,
traveling, and socializing, on a diel cycle (24-hour cycle). Disruption
of such functions resulting from reactions to stressors such as sound
exposure are more likely to be significant if they last more than one
diel cycle or recur on subsequent days (Southall et al., 2007).
Consequently, a behavioral response lasting less than one day and not
recurring on subsequent days is not considered particularly severe
unless it could directly affect reproduction or survival (Southall et
al., 2007). Note that there is a difference between multi-day
substantive (i.e., meaningful) behavioral reactions and multi-day
anthropogenic activities. For example, just because an activity lasts
for multiple days does not necessarily mean that individual animals are
either exposed to activity-related stressors for multiple days or,
further, exposed in a manner resulting in sustained multi-day
substantive behavioral responses.
Physiological stress responses. An animal's perception of a threat
may be sufficient to trigger stress responses consisting of some
combination of behavioral responses, autonomic nervous system
responses, neuroendocrine responses, or immune responses (e.g., Selye,
1950; Moberg, 2000). In many cases, an animal's first and sometimes
most economical (in terms of energetic costs) response is behavioral
avoidance of the potential stressor. Autonomic nervous system responses
to stress typically involve changes in heart rate, blood pressure, and
gastrointestinal activity. These responses have a relatively short
duration and may or may not have a significant long-term effect on an
animal's fitness.
Neuroendocrine stress responses often involve the hypothalamus-
pituitary-adrenal system. Virtually all neuroendocrine functions that
are affected by stress, including immune competence, reproduction,
metabolism, and behavior--are regulated by pituitary hormones. Stress-
induced changes in the secretion of pituitary hormones have been
implicated in failed reproduction, altered metabolism, reduced immune
competence, and behavioral disturbance (e.g., Moberg, 1987; Blecha,
2000). Increases in the circulation of glucocorticoids are also equated
with stress (Romano et al., 2004).
The primary distinction between stress (which is adaptive and does
not normally place an animal at risk) and ``distress'' is the cost of
the response. During a stress response, an animal uses glycogen stores
that can be quickly replenished once the stress is alleviated. In such
circumstances, the cost of the stress response would not pose serious
fitness consequences. However, when an animal does not have sufficient
energy reserves to satisfy the energetic costs of a stress response,
energy resources must be diverted from other functions. This state of
distress will last until the animal replenishes its energetic reserves
sufficient to restore normal function.
Relationships between these physiological mechanisms, animal
behavior, and the costs of stress responses are well-studied through
controlled experiments and for both laboratory and free-ranging animals
(e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003;
Krausman et al., 2004; Lankford et al., 2005; Ayres et al., 2012; Yang
et al., 2022). Stress responses due to exposure to anthropogenic sounds
or other stressors and their effects on marine mammals have also been
reviewed (Fair and Becker, 2000; Romano et al., 2002b) and, more
rarely, studied in wild populations (e.g., Romano et al., 2002a). For
example, Rolland et al. (2012) found that noise reduction from reduced
ship traffic in the Bay of Fundy was associated with decreased stress
in North Atlantic right whales. In addition, Lemos et al. (2022)
observed a correlation between higher levels of fecal glucocorticoid
metabolite concentrations (indicative of a stress response) and vessel
traffic in gray whales. Yang et al. (2022) studied behavioral and
physiological responses in captive bottlenose dolphins exposed to
playbacks of ``pile-driving-like'' impulsive sounds, finding
significant changes in cortisol and other
[[Page 21435]]
physiological indicators but only minor behavioral changes. These and
other studies lead to a reasonable expectation that some marine mammals
will experience physiological stress responses upon exposure to
acoustic stressors and that it is possible that some of these would be
classified as ``distress.'' In addition, any animal experiencing TTS
would likely also experience stress responses (NRC, 2005), however
distress is an unlikely result of this project based on observations of
marine mammals during previous, similar construction projects.
Norman (2011) reviewed environmental and anthropogenic stressors
for Cook Inlet beluga whales. Lyamin et al. (2011) determined that the
heart rate of a beluga whale increases in response to noise, depending
on the frequency and intensity. Acceleration of heart rate in the
beluga whale is the first component of the ``acoustic startle
response.'' Romano et al. (2004) demonstrated that captive beluga
whales exposed to high-level impulsive sounds (i.e., seismic airgun
and/or single pure tones up to 201 dB root-mean-square (RMS))
resembling sonar pings showed increased stress hormone levels of
norepinephrine, epinephrine, and dopamine when TTS was reached. Thomas
et al. (1990) exposed beluga whales to playbacks of an oil-drilling
platform in operation (``Sedco 708,'' 40 Hz-20 kHz; source level 153
dB). Ambient SPL at ambient conditions in the pool before playbacks was
106 dB and 134 to 137 dB RMS during playbacks at the monitoring
hydrophone across the pool. All cell and platelet counts and 21
different blood chemicals, including epinephrine and norepinephrine,
were within normal limits throughout baseline and playback periods, and
stress response hormone levels did not increase immediately after
playbacks. The difference between the Romano et al. (2004) and Thomas
et al. (1990) studies could be the differences in the type of sound
(seismic airgun and/or tone versus oil drilling), the intensity and
duration of the sound, the individual's response, and the surrounding
circumstances of the individual's environment. The sounds in the Thomas
et al. (1990) study would be more similar to those anticipated by the
FHWA's activities; therefore, no more than short-term, low-hormone
stress responses, if any, are expected as a result of exposure to noise
from the FHWA's activities.
Vocalizations and Auditory Masking. Since many marine mammals rely
on sound to find prey, moderate social interactions, and facilitate
mating (Tyack, 2008), noise from anthropogenic sound sources can
interfere with these functions, but only if the noise spectrum overlaps
with the hearing sensitivity of the receiving marine mammal (Southall
et al., 2007; Clark et al., 2009; Hatch et al., 2012). Chronic exposure
to excessive, though not high-intensity, noise could cause masking at
particular frequencies for marine mammals that utilize sound for vital
biological functions (Clark et al., 2009). Acoustic masking is when
other noises such as from human sources interfere with an animal's
ability to detect, recognize, or discriminate between acoustic signals
of interest (e.g., those used for intraspecific communication and
social interactions, prey detection, predator avoidance, navigation)
(Richardson et al., 1995; Erbe et al., 2016). Therefore, under certain
circumstances, marine mammals whose acoustical sensors or environment
are being severely masked could also be impaired from maximizing their
performance fitness in survival and reproduction. The ability of a
noise source to mask biologically important sounds depends on the
characteristics of both the noise source and the signal of interest
(e.g., signal-to-noise ratio, temporal variability, direction), in
relation to each other and to an animal's hearing abilities (e.g.,
sensitivity, frequency range, critical ratios, frequency
discrimination, directional discrimination, age or TTS hearing loss),
and existing ambient noise and propagation conditions (Hotchkin and
Parks, 2013).
Marine mammals vocalize for different purposes and across multiple
modes, such as whistling, echolocation click production, calling, and
singing. Changes in vocalization behavior in response to anthropogenic
noise can occur for any of these modes and may result from a need to
compete with an increase in background noise or may reflect increased
vigilance or a startle response. For example, in the presence of
potentially masking signals, humpback whales and killer whales (Orcinus
orca) have been observed to increase the length of their songs (Miller
et al., 2000; Fristrup et al., 2003) or vocalizations (Foote et al.,
2004), respectively, while North Atlantic right whales (Eubalaena
glacialis) have been observed to shift the frequency content of their
calls upward while reducing the rate of calling in areas of increased
anthropogenic noise (Parks et al., 2007). Fin whales (Balaenoptera
physalus) have also been documented lowering the bandwidth, peak
frequency, and center frequency of their vocalizations under increased
levels of background noise from large vessels (Castellote et al.,
2012). Other alterations to communication signals have also been
observed. For example, gray whales, in response to playback experiments
exposing them to vessel noise, have been observed increasing their
vocalization rate and producing louder signals at times of increased
outboard engine noise (Dahlheim and Castellote, 2016). Alternatively,
in some cases, animals may cease sound production during production of
aversive signals (Bowles et al., 1994, Wisniewska et al., 2018).
Under certain circumstances, marine mammals experiencing
significant masking could also be impaired from maximizing their
performance fitness in survival and reproduction. Therefore, when the
coincident (masking) sound is human-made, it may be considered
harassment when disrupting or altering critical behaviors. It is
important to distinguish TTS and PTS, which persist after the sound
exposure, from masking, which occurs during the sound exposure. Because
masking (without resulting in TS) is not associated with abnormal
physiological function, it is not considered a physiological effect,
but rather a potential behavioral effect (though not necessarily one
that would be associated with harassment).
The frequency range of the potentially masking sound is important
in determining any potential behavioral impacts. For example, low-
frequency signals may have less effect on high-frequency echolocation
sounds produced by odontocetes but are more likely to affect detection
of mysticete communication calls and other potentially important
natural sounds such as those produced by surf and some prey species.
The masking of communication signals by anthropogenic noise may be
considered as a reduction in the communication space of animals (e.g.,
Clark et al., 2009) and may result in energetic or other costs as
animals change their vocalization behavior (e.g., Miller et al., 2000;
Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2010; Holt
et al., 2009). Masking can be reduced in situations where the signal
and noise come from different directions (Richardson et al., 1995),
through amplitude modulation of the signal, or through other
compensatory behaviors, including modifications of the acoustic
properties of the signal or the signaling behavior (Hotchkin and Parks,
2013). Masking can be tested directly in captive species (e.g., Erbe,
2008), but in wild populations it must be either modeled or inferred
from evidence of masking compensation. There are few studies addressing
real-world masking
[[Page 21436]]
sounds likely to be experienced by marine mammals in the wild (e.g.,
Branstetter et al., 2013).
Masking occurs in the frequency band that the animals utilize and
is more likely to occur in the presence of broadband, relatively
continuous noise sources such as vibratory pile driving. Energy
distribution of vibratory pile driving sound covers a broad frequency
spectrum and is anticipated to be within the audible range of marine
mammals present in the proposed action area. Since noises generated
from the proposed construction activities are mostly concentrated at
low frequencies (< 2 kHz), these activities likely have less effect on
mid-frequency echolocation sounds produced by odontocetes (toothed
whales). However, lower frequency noises are more likely to affect
detection of communication calls and other potentially important
natural sounds such as surf and prey noise. Low-frequency noise may
also affect communication signals when they occur near the frequency
band for noise and thus reduce the communication space of animals
(e.g., Clark et al., 2009) and cause increased stress levels (e.g.,
Holt et al., 2009). Unlike TS, masking, which can occur over large
temporal and spatial scales, can potentially affect the species at
population, community, or even ecosystem levels, in addition to
individual levels. Masking affects both senders and receivers of the
signals, and at higher levels for longer durations, could have long-
term chronic effects on marine mammal species and populations. However,
the noise generated by the FHWA's proposed activities will only occur
intermittently, across an estimated 234 days in year 1 and 193 days in
year 2 during the authorization period in a relatively small area
focused around the proposed construction site. Thus, while the FHWA's
proposed activities may mask some acoustic signals that are relevant to
the daily behavior of marine mammals, the short-term duration and
limited areas affected make it very unlikely that the fitness of
individual marine mammals would be impacted.
Potential Effects on Marine Mammal Habitat
The FHWA's proposed activities could have localized, temporary
impacts on marine mammal habitat, including prey, by increasing in-
water SPLs. Increased noise levels may affect acoustic habitat and
adversely affect marine mammal prey in the vicinity of the project
areas (see discussion below). Elevated levels of underwater noise would
ensonify the project areas where both fishes and mammals occur and
could affect foraging success. Additionally, marine mammals may avoid
the area during the proposed construction activities; however,
displacement due to noise is expected to be temporary and is not
expected to result in long-term effects to the individuals or
populations.
The total area likely impacted by the FHWA's activities is
relatively small compared to the available habitat in upper Chesapeake
Bay and the Patapsco River. Avoidance by potential prey (i.e., fish) of
the immediate area due to increased noise is possible. The duration of
fish and marine mammal avoidance of this area after pile installation
and associated activities stops is unknown, but a rapid return to
normal recruitment, distribution, and behavior is anticipated. Any
behavioral avoidance by fish or marine mammals of the disturbed area
would still leave significantly large areas of fish and marine mammal
foraging habitat in the nearby vicinity.
The proposed project will occur within the same footprint as
existing marine infrastructure. The nearshore and intertidal habitat
where the proposed project will occur is an area of relatively high
marine vessel traffic. Most marine mammals do not generally use the
area within the footprint of the project area. Temporary, intermittent,
and short-term habitat alteration may result from increased noise
levels during the proposed construction activities. Effects on marine
mammals will be limited to temporary displacement from pile
installation and removal noise, and effects on prey species will be
similarly limited in time and space.
Water quality. Temporary and localized reduction in water quality
will occur as a result of in-water construction activities. Most of
this effect would occur during the installation and removal of piles
when bottom sediments are disturbed. The installation and removal of
piles would disturb bottom sediments and may cause a temporary increase
in suspended sediment in the project area. During pile extraction (if
necessary), sediment attached to the pile moves vertically through the
water column until gravitational forces cause it to slough off under
its own weight. The small resulting sediment plume is expected to
settle out of the water column within a few hours. Studies of the
effects of turbid water on fish (marine mammal prey) suggest that
concentrations of suspended sediment can reach thousands of milligrams
per liter before an acute toxic reaction is expected (Burton, 1993).
Effects to turbidity and sedimentation are expected to be short-
term, minor, and localized. Since the currents are so strong in the
area, following the completion of sediment-disturbing activities,
suspended sediments in the water column should dissipate and quickly
return to background levels in all construction scenarios. Turbidity
within the water column has the potential to reduce the level of oxygen
in the water and irritate the gills of prey fish species in the
proposed project area. However, turbidity plumes associated with the
project would be temporary and localized, and fish in the proposed
project area would be able to move away from and avoid the areas where
plumes may occur. Therefore, it is expected that the impacts on prey
fish species from turbidity, and therefore on marine mammals, would be
minimal and temporary. In general, the area likely impacted by the
proposed construction activities is relatively small compared to the
available marine mammal habitat in the upper Chesapeake Bay and
Patapsco River.
Potential Effects on Prey. Sound may affect marine mammals through
impacts on the abundance, behavior, or distribution of prey species
(e.g., crustaceans, cephalopods, fishes, zooplankton). Marine mammal
prey varies by species, season, and location and, for some, is not well
documented. Studies regarding the effects of noise on known marine
mammal prey are described here.
Fishes utilize the soundscape and components of sound in their
environment to perform important functions such as foraging, predator
avoidance, mating, and spawning (e.g., Zelick et al., 1999; Fay, 2009).
Depending on their hearing anatomy and peripheral sensory structures,
which vary among species, fishes hear sounds using pressure and
particle motion sensitivity capabilities and detect the motion of
surrounding water (Fay et al., 2008). The potential effects of noise on
fishes depends on the overlapping frequency range, distance from the
sound source, water depth of exposure, and species-specific hearing
sensitivity, anatomy, and physiology. Key impacts to fishes may include
behavioral responses, hearing damage, barotrauma (pressure-related
injuries), and mortality.
Fish react to sounds that are especially strong and/or intermittent
low-frequency sounds, and behavioral responses such as flight or
avoidance are the most likely effects. Short duration, sharp sounds can
cause overt or subtle changes in fish behavior and local distribution.
The reaction of fish to
[[Page 21437]]
noise depends on the physiological state of the fish, past exposures,
motivation (e.g., feeding, spawning, migration), and other
environmental factors. Hastings and Popper (2005) identified several
studies that suggest fish may relocate to avoid certain areas of sound
energy. Additional studies have documented effects of pile driving on
fishes (e.g., Scholik and Yan, 2001, 2002; Popper and Hastings, 2009).
Several studies have demonstrated that impulse sounds might affect the
distribution and behavior of some fishes, potentially impacting
foraging opportunities or increasing energetic costs (e.g., Fewtrell
and McCauley, 2012; Pearson et al., 1992; Skalski et al., 1992;
Santulli et al., 1999; Paxton et al., 2017). However, some studies have
shown no or slight reaction to impulse sounds (e.g., Pe[ntilde]a et
al., 2013; Wardle et al., 2001; Jorgenson and Gyselman, 2009; Cott et
al., 2012). More commonly, though, the impacts of noise on fishes are
temporary.
SPLs of sufficient strength have been known to cause injury to
fishes and fish mortality (summarized in Popper et al., 2014). However,
in most fish species, hair cells in the ear continuously regenerate and
loss of auditory function likely is restored when damaged cells are
replaced with new cells. Halvorsen et al. (2012b) showed that a TTS of
4 to 6 dB was recoverable within 24 hours for one species. Impacts
would be most severe when the individual fish is close to the source
and when the duration of exposure is long. Injury caused by barotrauma
can range from slight to severe and can cause death, and is most likely
for fish with swim bladders. Barotrauma injuries have been documented
during controlled exposure to impact pile driving (Halvorsen et al.,
2012a; Casper et al., 2013, 2017).
Fish populations in the proposed project area that serve as marine
mammal prey could be temporarily affected by noise from pile
installation and removal. The frequency range in which fishes generally
perceive underwater sounds is 50 to 2,000 Hz, with peak sensitivities
below 800 Hz (Popper and Hastings, 2009). Fish behavior or distribution
may change, especially with strong and/or intermittent sounds that
could harm fishes. High underwater SPLs have been documented to alter
behavior, cause hearing loss, and injure or kill individual fish by
causing serious internal injury (Hastings and Popper, 2005).
Zooplankton is a food source for several marine mammal species, as
well as a food source for fish that are then preyed upon by marine
mammals. Population effects on zooplankton could have indirect effects
on marine mammals. Data are limited on the effects of underwater sound
on zooplankton species, particularly sound from construction (Erbe et
al., 2019). Popper and Hastings (2009) reviewed information on the
effects of human-generated sound and concluded that no substantive data
are available on whether the sound levels from pile driving, seismic
activity, or any human-made sound would have physiological effects on
invertebrates. Any such effects would be limited to the area very near
(1 to 5 m) the sound source and would result in no population effects
because of the relatively small area affected at any one time and the
reproductive strategy of most zooplankton species (short generation,
high fecundity, and very high natural mortality). No adverse impact on
zooplankton populations is expected to occur from the specified
activity due, in part, to large reproductive capacities and naturally
high levels of predation and mortality of these populations. Any
mortalities or impacts that might occur would be negligible.
The greatest potential impact to marine mammal prey during
construction would occur during impact pile driving. Impact driving
would be attenuated with bubble curtains during all months, reducing
the potential for injurious effects on prey species. In-water
construction activities would typically occur during daylight hours,
allowing fish to forage and transit the project area in the evening.
Vibratory pile driving may elicit behavioral reactions from fishes such
as temporary avoidance of the area but is unlikely to cause injuries to
fishes or have persistent effects on local fish populations.
Construction would have minimal permanent and temporary impacts on
benthic invertebrate species, a marine mammal prey source. In addition,
it should be noted that the area in question is low-quality habitat
since it is already highly developed and experiences a high level of
anthropogenic noise from normal operations and other vessel traffic.
Potential Effects on Foraging Habitat
The FSK Bridge Rebuild project is not expected to result in any
habitat-related effects that could cause significant or long-term
negative consequences for individual marine mammals or their
populations, since installation and removal of in-water piles would be
temporary and intermittent. The total seafloor area affected by pile
installation and removal is a very small area compared to the vast
foraging area available to marine mammals outside this project area.
The mouth of the Patapsco River and the northern portion of the
Chesapeake Bay are at best peripheral habitat for dolphins and not
expected to include any foraging areas of particular importance. The
area impacted by the project is relatively small compared to the
available habitat just outside the project area, and there are no areas
of particular significance that would be impacted by this project. Any
behavioral avoidance by fish of the disturbed area would still leave
significantly large areas of fish and marine mammal foraging habitat in
the nearby vicinity. As described in the preceding, the potential for
the FHWA's construction to affect the availability of prey to marine
mammals or to meaningfully impact the quality of physical or acoustic
habitat is considered to be insignificant. Therefore, impacts of the
project are not likely to have adverse effects on marine mammal
foraging habitat in the proposed project area.
In summary, given the relatively small areas being affected, as
well as the temporary and mostly transitory nature of the proposed
construction activities, any adverse effects from the FHWA's activities
on prey habitat or prey populations are expected to be minor and
temporary. The most likely impact to fishes at the project site would
be temporary avoidance of the area. Any behavioral avoidance by fish of
the disturbed area would still leave significantly large areas of fish
and marine mammal foraging habitat in the nearby vicinity. Thus, we
preliminarily conclude that impacts of the specified activities are not
likely to have more than short-term adverse effects on any prey habitat
or populations of prey species. Further, any impacts to marine mammal
habitat are not expected to result in significant or long-term
consequences for individual marine mammals, or to contribute to adverse
impacts on their populations.
Estimated Take of Marine Mammals
This section provides an estimate of the number of incidental takes
proposed for authorization through the IHA, which will inform NMFS'
consideration of ``small numbers,'' the negligible impact
determinations, and impacts on subsistence uses.
Harassment is the only type of take expected to result from these
activities. Except with respect to certain activities not pertinent
here, section 3(18) of the MMPA defines ``harassment'' as any act of
pursuit, torment, or annoyance, which (i) has the potential to injure a
marine mammal or marine mammal stock in the wild (Level A harassment);
[[Page 21438]]
or (ii) has the potential to disturb a marine mammal or marine mammal
stock in the wild by causing disruption of behavioral patterns,
including, but not limited to, migration, breathing, nursing, breeding,
feeding, or sheltering (Level B harassment).
Authorized takes would be by Level B harassment only, in the form
of behavioral reactions and/or TTS for individual marine mammals
resulting from exposure to impact and vibratory pile driving. Based on
the nature of the activity and the anticipated effectiveness of the
mitigation measures (i.e., shutdown zones and bubble curtains)
discussed in detail below in the Proposed Mitigation section, Level A
harassment is neither anticipated nor proposed to be authorized.
As described previously, no serious injury or mortality is
anticipated or proposed to be authorized for this activity. Below we
describe how the proposed take numbers are estimated.
For acoustic impacts, generally speaking, we estimate take by
considering: (1) acoustic criteria above which NMFS believes there is
some reasonable potential for marine mammals to be behaviorally
harassed or incur some degree of AUD INJ; (2) the area or volume of
water that will be ensonified above these levels in a day; (3) the
density or occurrence of marine mammals within these ensonified areas;
and, (4) the number of days of activities. We note that while these
factors can contribute to a basic calculation to provide an initial
prediction of potential takes, additional information that can
qualitatively inform take estimates is also sometimes available (e.g.,
previous monitoring results or average group size). Below, we describe
the factors considered here in more detail and present the proposed
take estimates.
Acoustic Criteria
NMFS recommends the use of acoustic criteria that identify the
received level of underwater sound above which exposed marine mammals
would be reasonably expected to be behaviorally harassed (equated to
Level B harassment) or to incur AUD INJ of some degree (equated to
Level A harassment).
Level B Harassment--Though significantly driven by received level,
the onset of behavioral disturbance from anthropogenic noise exposure
is also informed to varying degrees by other factors related to the
source or exposure context (e.g., frequency, predictability, duty
cycle, duration of the exposure, signal-to-noise ratio, distance to the
source), the environment (e.g., bathymetry, other noises in the area,
predators in the area), and the receiving animals (hearing, motivation,
experience, demography, life stage, depth) and can be difficult to
predict (e.g., Southall et al., 2007; Southall et al., 2021; Ellison et
al., 2012). Based on what the available science indicates and the
practical need to use a threshold based on a metric that is both
predictable and measurable for most activities, NMFS typically uses a
generalized acoustic threshold based on received level to estimate the
onset of behavioral harassment. NMFS generally predicts that marine
mammals are likely to be behaviorally harassed in a manner considered
to be Level B harassment when exposed to underwater anthropogenic noise
above RMS SPL of 120 dB re 1 [mu]Pa) for continuous (e.g., vibratory
pile driving, drilling) and above RMS SPL 160 dB re 1 [mu]Pa for non-
explosive impulsive (e.g., seismic airguns) or intermittent (e.g.,
scientific sonar) sources. Generally, Level B harassment take estimates
based on these behavioral harassment thresholds are expected to include
any likely takes by TTS as, in most cases, the likelihood of TTS occurs
at distances from the source less than those at which behavioral
harassment is likely. TTS of a sufficient degree can manifest as
behavioral harassment, as reduced hearing sensitivity and the potential
reduced opportunities to detect important signals (conspecific
communication, predators, prey) may result in changes in behavior
patterns that would not otherwise occur.
FHWA's proposed activity includes the use of continuous non-
impulsive and impulsive sources, and therefore the RMS SPL thresholds
of 120 dB and 160 dB re 1[micro]Pa are applicable.
Level A harassment. NMFS' Updated Technical Guidance for Assessing
the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version
3.0) (Updated Technical Guidance, 2024) identifies dual criteria to
assess AUD INJ (Level A harassment) to five different underwater marine
mammal groups (based on hearing sensitivity) as a result of exposure to
noise from two different types of sources (impulsive or non-impulsive).
FHWA's proposed activity includes the use of impulsive (impact driving)
and non-impulsive (vibratory driving) sources.
The 2024 Updated Technical Guidance criteria include both updated
thresholds and updated weighting functions for each hearing group. The
thresholds are provided in table 6, below. The references, analysis,
and methodology used in the development of the criteria are described
in NMFS' 2024 Updated Technical Guidance, which may be accessed at:
<a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools">https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance-other-acoustic-tools</a>.
Table 6--Thresholds Identifying the Onset of Auditory Injury
----------------------------------------------------------------------------------------------------------------
AUD INJ onset acoustic thresholds * (received level)
Hearing group ------------------------------------------------------------------------
Impulsive Non-impulsive
----------------------------------------------------------------------------------------------------------------
Low-Frequency (LF) Cetaceans........... Cell 1: Lpk,flat: 222 dB; Cell 2: LE,LF,24h: 197 dB.
LE,LF,24h: 183 dB.
High-Frequency (HF) Cetaceans.......... Cell 3: Lpk,flat: 230 dB; Cell 4: LE,HF,24h: 201 dB.
LE,HF,24h: 193 dB.
Very High-Frequency (VHF) Cetaceans.... Cell 5: Lpk,flat: 202 dB; Cell 6: LE,VHF,24h: 181 dB.
LE,VHF,24h: 159 dB.
Phocid Pinnipeds (PW) (Underwater)..... Cell 7: Lpk,flat: 223 dB; Cell 8: LE,PW,24h: 195 dB.
LE,PW,24h: 183 dB.
Otariid Pinnipeds (OW) (Underwater).... Cell 9: Lpk,flat: 230 dB; Cell 10: LE,OW,24h: 199 dB.
LE,OW,24h: 185 dB.
----------------------------------------------------------------------------------------------------------------
* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for
calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure
level criteria associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-
impulsive sources.
[[Page 21439]]
Note: Peak sound pressure level (Lp,0-pk) has a reference value of 1 [mu]Pa, and weighted cumulative sound
exposure level (LE,p) has a reference value of 1 [mu]Pa\2\s. In this table, criteria are abbreviated to be
more reflective of International Organization for Standardization standards (ISO, 2017). The subscript
``flat'' is being included to indicate peak sound pressure are flat weighted or unweighted within the
generalized hearing range of marine mammals underwater (i.e., 7 Hz to 165 kHz). The subscript associated with
cumulative sound exposure level criteria indicates the designated marine mammal auditory weighting function
(LF, HF, and VHF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours.
The weighted cumulative sound exposure level criteria could be exceeded in a multitude of ways (i.e., varying
exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate
the conditions under which these criteria will be exceeded.
Ensonified Area
Here, we describe operational and environmental parameters of the
activity that are used in estimating the area ensonified above the
acoustic thresholds, including source levels and transmission loss
coefficient.
The ensonified areas associated with the proposed pile driving
activities were modeled by FHWA and JASCO Applied Sciences during the
application preparation process (JASCO 2025), and the resulting
predictions were verified in the field via hydroacoustic monitoring
during a test-pile program during the fall of 2025. During monitoring,
the source values associated with impact and vibratory driving of 96-in
steel pipe piles were determined, as well as effectiveness of two
separate noise attenuation systems, finding that for impact driving the
bubble curtain attenuated source values by approximately 26.3 dB, and
for vibratory by approximately 6 dB (see Proposed Mitigation, below).
Sound propagation modeling performed prior to the test-pile
monitoring was found to be conservative as measured isopleths were
smaller than expected in the modeling. The numerical model likely
underestimated the true propagation loss, resulting in an over
estimation of the sound propagation distances in this environment, as
reflected by the measured data. Therefore, FHWA used the measured
values from October 2025 for attenuated impact and vibratory driving in
the prediction of ensonified areas for the work to be performed in
Years 1 and 2 of the FSK Bridge rebuild project. For unattenuated
vibratory driving, FHWA modeled with a source level increased by 10 dB
based on predicted bubble curtain performance, although the measured
performance was only 6 dB. Thus, increasing the source value by 10 dB
is conservative.
One impact and one vibratory hammer were used during the test-pile
program (table 7). The results of the test-pile driving indicated a
need for larger hammers for all vibratory pile installation and for
approximately 20 percent of impact pile installation. Source values for
the larger hammers were approximated based on the measured results of
the test-pile sound levels and the ratios of the driving forces or
hammer energies; for further detail, please refer to the IHA
application.
Table 7--Measured and Predicted Source Values for Each Hammer Type for 96-in Steel Piles
----------------------------------------------------------------------------------------------------------------
Attenuated SPL Unattenuated
Method Hammer details at 10 m SPL at 10 m
----------------------------------------------------------------------------------------------------------------
Impact (measured during test pile and Menck MHU 800S Energy = 820 \a\ 196.8 \a\ 209.9
estimated for 80% of production driving). kilojoules (kJ) Hammer weight =
793 kiloNewtons (kN).
Impact (estimated for 20% of production Menck 1900, or similar Energy = \b\ 199. \c\
driving). 1900 kJ Hammer weight = 1,574
kN.
Vibratory (measured during test pile)......... APE 600 Driving force = 4,434 kN 168 \d\ 178
Hammer weight = 275 kN 22.5 Hz
working frequency.
Vibratory (estimated for production driving).. ICE 200-C Driving force = 7,104 \b\ 170 \d\ 180
kN Hammer weight = 345 kN 26 Hz
working frequency.
----------------------------------------------------------------------------------------------------------------
\a\ The attenuated measured value for all 11 test piles is shown. For the 2 test piles with on/off bubble
curtain testing, the measured attenuated SPL averaged 183.2 dB RMS and measured unattenuated measured 209.9 dB
RMS. The bubble curtain effectiveness and unattenuated source level were based off the 2 piles with on/off
testing.
\b\ Value predicted based on ratio of hammer energies;
\c\ --No unattenuated impact pile driving is planned, and thus no unattenuated value for the larger impact
hammer was predicted or used in modeling;
\d\ Measured unattenuated source level of vibratory installation for a single pile during the test pile program
was 174 dB RMS, a 6 dB increase from attenuated measurements. However, modeling was completed before test pile
measurements were fully analyzed and assumed 10 dB effectiveness of the bubble curtain system, resulting in
overestimates of unattenuated source values.
Marine Mammal Occurrence
In this section we provide information about the occurrence of
marine mammals, including density or other relevant information which
will inform the take calculations. Rodriguez et al. (2021) synthesizes
three consecutive years (2017, 2018, and 2019) of data from the
DolphinWatch app collected between the months of April (2018 and 2019)
and October (2017, 2018, and 2019). Data collection began in late June
2017. Overall, the highest dolphin sightings were correlated with water
temperatures between 24 and 30 degrees Celsius (75.2 to 86 degrees
Fahrenheit). Dolphins were sighted most in the summer, peaking in July
of each year. Salinity and tidal state also influenced the
spatiotemporal occurrence of bottlenose dolphins.
Density estimates for the upper Chesapeake Bay region were compiled
for each year (table 8) and the geometric mean of all three years was
used to estimate dolphin densities for the purpose of this analysis.
Although dolphin densities are expected to be lower during spring and
fall (no dolphins were sighted in the upper bay region during April,
May, September, and October of 2018, with other years following a
similar pattern), FHWA determined, and NMFS agrees, that the geometric
mean density incorporates the confirmed dolphin sightings across
spring, summer, and fall, and is suitable to estimate presence in all
three seasons. Winter density of dolphins in the area is estimated at
zero, as no dolphins were sighted in the shoulder months in the upper
bay, and dolphins are not expected to be present in the project area
during the months of December through February.
[[Page 21440]]
Table 8--Dolphin Density Based on Rodriguez et al. 2021
----------------------------------------------------------------------------------------------------------------
Yearly (March-November)
Year average density (per Geometric mean density
km\2\) (per km\2\)
----------------------------------------------------------------------------------------------------------------
2017...................................................... 0.015 0.019
2018...................................................... 0.026
2019...................................................... 0.017
----------------------------------------------------------------------------------------------------------------
Take Estimation
Here we describe how the information provided above is synthesized
to produce a quantitative estimate of the take that is reasonably
likely to occur and proposed for authorization.
Estimated take by Level B harassment was calculated based on the
ensonified areas multiplied by the seasonal density estimates and the
number of in-water workdays in each season for each year. The
approximate number of workdays per season includes concurrent driving,
and has been limited to the maximum number of days in the appropriate
months. The calculated daily, seasonal, and total take estimates for
year 1 and year 2 are shown in tables 9 and 10, respectively.
Table 9--Proposed Take Calculations for Year 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Level B Estimated
Method harassment Density Daily Number of days seasonal Proposed take
area (km\2\) exposures exposures
--------------------------------------------------------------------------------------------------------------------------------------------------------
Summer
--------------------------------------------------------------------------------------------------------------------------------------------------------
Impact (80%)............................................ 0.43 0.019 0.0082 63 0.52 12
Impact (20%)............................................ 0.64 0.0122 16 0.20
Vibratory (attenuated)\1\............................... 7.74 0.1471 79 11.62
--------------------------------------------------------------------------------------------------------------------------------------------------------
Fall and Spring
--------------------------------------------------------------------------------------------------------------------------------------------------------
Impact (80%)............................................ 0.43 0.019 0.0082 124 1.01 59
Impact (20%)............................................ 0.64 0.0122 31 0.38
Vibratory (unattenuated)\ 1\............................ 19.48 0.3701 155 57.37
-----------------------------------------------------------------------------------------------
Total Proposed Take................................. 71
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Bubble curtains are proposed for use during vibratory pile driving only between June 1 and September 30 due to expected increased dolphin presence
during the summer months. No bubble curtains would be used for vibratory driving outside of these dates.
Table 10--Proposed Take Calculations for Year 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Level B Estimated
Method harassment Density Daily Number of seasonal Proposed take
area (km\2\) exposures days exposures
--------------------------------------------------------------------------------------------------------------------------------------------------------
Summer
--------------------------------------------------------------------------------------------------------------------------------------------------------
Impact (80%)............................................ 0.43 0.019 0.0082 47 0.38 10
Impact (20%)............................................ 0.64 0.0122 12 0.15
Vibratory (attenuated).................................. 7.74 0.1471 67 9.85
--------------------------------------------------------------------------------------------------------------------------------------------------------
Fall and Spring
--------------------------------------------------------------------------------------------------------------------------------------------------------
Impact (80%)............................................ 0.43 0.0038 0.0082 44 0.36 21
Impact (20%)............................................ 0.64 0.0122 11 0.13
Vibratory (unattenuated)................................ 19.48 0.3701 55 20.36
-----------------------------------------------------------------------------------------------
Total Proposed Take................................. 31
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Bubble curtains are proposed for use during vibratory pile driving between June 1 and September 30 due to expected increased dolphin presence during
the summer months. No bubble curtains would be used for vibratory driving outside of these dates.
An estimate of take by Level A harassment was performed in the same
manner for days with impact pile driving. The Level A harassment area
for attenuated impact driving measured during the test pile program was
0.02 km\2\ for the smaller hammer; FHWA estimated a Level A harassment
area of 0.045 km\2\ for the larger impact hammer based on the measured
distance for the smaller hammer and the ratio of hammer energies
discussed previously. JASCO's acoustic model outputs indicated that the
threshold for onset of AUD INJ for HF cetaceans would not be reached
during vibratory pile driving (single and concurrent scenarios). Ranges
from the test pile project measurements of attenuated and unattenuated
vibratory pile driving were less than 10 m. Using the same number
[[Page 21441]]
of seasonal days as shown in tables 9 and 10, the estimates of take by
Level A harassment were 0.08 animals in Year 1, and 0.03 animals in
Year 2. Thus, FHWA did not request any take by Level A harassment, and
none is proposed for authorization. Tables 11 and 12 show the total
estimated take proposed for authorization and the percentages of stocks
taken for years 1 and 2, respectively.
Table 11--Estimated Proposed Take by Level A and Level B Harassment and Percent of Stocks Taken for Year 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stock Percent of
Species Stock Level A Level B Total abundance stock (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bottlenose dolphin..................... Western North Atlantic Northern 0 71 71 6,639 1.07
Migratory Coastal Stock.
Western North Atlantic Southern .............. .............. .............. 3,751 1.89
Migratory Coastal Stock.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Table 12--Estimated Proposed Take by Level A and Level B Harassment and Percent of Stocks Taken for Year 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Percent of
Species Stock Level A Level B Total Stock abundance stock (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bottlenose dolphin................... Western North Atlantic 0 31 31 6,639.................. 0.47
Northern Migratory
Coastal Stock.
Western North Atlantic .............. .............. .............. 3,751.................. 0.83
Southern Migratory
Coastal Stock.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Mitigation
In order to issue an IHA under section 101(a)(5)(D) of the MMPA,
NMFS must set forth the permissible methods of taking pursuant to the
activity, and other means of effecting the least practicable impact on
the species or stock and its habitat, paying particular attention to
rookeries, mating grounds, and areas of similar significance, and on
the availability of the species or stock for taking for certain
subsistence uses (latter not applicable for this action). NMFS
regulations require applicants for incidental take authorizations to
include information about the availability and feasibility (economic
and technological) of equipment, methods, and manner of conducting the
activity or other means of effecting the least practicable adverse
impact upon the affected species or stocks, and their habitat (50 CFR
216.104(a)(11)).
In evaluating how mitigation may or may not be appropriate to
ensure the least practicable adverse impact on species or stocks and
their habitat, as well as subsistence uses where applicable, NMFS
considers two primary factors:
(1) The manner in which, and the degree to which, the successful
implementation of the measure(s) is expected to reduce impacts to
marine mammals, marine mammal species or stocks, and their habitat.
This considers the nature of the potential adverse impact being
mitigated (likelihood, scope, range). It further considers the
likelihood that the measure will be effective if implemented
(probability of accomplishing the mitigating result if implemented as
planned), the likelihood of effective implementation (probability
implemented as planned); and
(2) The practicability of the measures for applicant
implementation, which may consider such things as cost and impact on
operations.
The mitigation requirements described in the following were
proposed by FHWA in its adequate and complete application or are the
result of subsequent coordination between NMFS and FHWA. FHWA has
agreed that all of the mitigation measures are practicable. NMFS has
fully reviewed the specified activities and the mitigation measures to
determine if the mitigation measures would result in the least
practicable adverse impact on marine mammals and their habitat, as
required by the MMPA, and has determined the proposed measures are
appropriate. NMFS describes these below as proposed mitigation
requirements, and has included them in the proposed IHAs.
In addition to the measures described later in this section, the
FHWA would follow these general mitigation measures:
<bullet> Authorized take, by Level B harassment only, would be
limited to the species and numbers listed in tables 11 and 12 for years
1 and 2, respectively. Construction activities must be halted upon
observation of either a species for which incidental take is not
authorized or a species for which incidental take has been authorized
but the authorized number of takes has been met, entering or within the
harassment zone.
<bullet> The taking by serious injury or death of any of the
species listed in tables 11 and 12 or any taking of any other species
of marine mammal would be prohibited and may result in the
modification, suspension, or revocation of the IHAs, if issued. Any
taking exceeding the authorized amounts listed in in tables 11 and 12
would be prohibited and may result in the modification, suspension, or
revocation of the IHAs, if issued.
<bullet> Ensure that construction supervisors and crews, the marine
mammal monitoring team, and relevant FHWA staff are trained prior to
the start of all construction activities, so that responsibilities,
communication procedures, marine mammal monitoring protocol, and
operational procedures are clearly understood. New personnel joining
during the project must be trained prior to commencing work;
<bullet> The FHWA, construction supervisors and crews, Protected
Species Observers (PSOs), and relevant FHWA staff must avoid direct
physical interaction with marine mammals
[[Page 21442]]
during construction activity. If a marine mammal comes within 10 m of
such activity, operations must cease and vessels must reduce speed to
the minimum level required to maintain steerage and safe working
conditions, as necessary to avoid direct physical interaction.
<bullet> Employ PSOs and establish monitoring locations as
described in section 5 of the IHA and the FHWA's Marine Mammal
Monitoring and Mitigation Plan. The FHWA must monitor the project area
to the maximum extent possible based on the required number of PSOs,
required monitoring locations, and environmental conditions;
Additionally, the following mitigation measures apply to the FHWA's
in-water construction activities:
Establishment of Shutdown Zones--The FHWA would establish shutdown
zones with radial distances as identified in table 13 for all
construction activities. If a marine mammal is observed entering or
within the shutdown zones indicated in table 13, pile driving activity
must be delayed or halted. If pile driving is delayed or halted due to
the presence of a marine mammal, the activity may not commence or
resume until either the animal has voluntarily exited and been visually
confirmed beyond the shutdown zones or 15 minutes have passed without
re-detection of the animal.
Table 13--Proposed Shutdown Zones During Project Activities
----------------------------------------------------------------------------------------------------------------
Monitoring
Activity Season Shutdown zone zone (Level B)
(m) (m)
----------------------------------------------------------------------------------------------------------------
Impact--small hammer.......................... All............................. 80 370
Impact--large hammer.......................... All............................. 120 450
Vibratory (Single Hammer)..................... Summer.......................... 10 1,330
Fall, Winter, Spring............ 10 2,200
Vibratory (Concurrent)........................ Summer.......................... 10 1,570
Fall, Winter, Spring............ 10 2,490
----------------------------------------------------------------------------------------------------------------
Pre- and Post-Activity Monitoring--Monitoring would take place from
30 minutes prior to initiation of pile driving activity (i.e., pre-
start clearance monitoring) through 30 minutes post-completion of pile
driving activity. In addition, monitoring for 30 minutes would take
place whenever a break in the specified activity (i.e., impact pile
driving, vibratory pile driving) of 30 minutes or longer occurs. Pre-
start clearance monitoring would be conducted during periods of
visibility sufficient for the lead PSO to determine that the shutdown
zones indicated in table 13 are clear of marine mammals. Pile driving
may commence following 30 minutes of observation when the determination
is made that the shutdown zones are clear of marine mammals.
If nighttime pile driving is required, PSOs will continue
monitoring using infrared goggles or other night-vision equipment.
Additionally, the shutdown zones will be illuminated during any night
pile driving.
Soft Start--The FHWA would use soft start techniques when impact
pile driving. Soft start requires contractors to provide an initial set
of three strikes at reduced energy, followed by a 30-second (sec)
waiting period, then two subsequent reduced-energy strike sets. A soft
start would be implemented at the start of each day's impact pile
driving and at any time following cessation of impact pile driving for
a period of 30 minutes or longer. Soft start procedures are used to
provide additional protection to marine mammals by providing warning
and/or giving marine mammals a chance to leave the area prior to the
hammer operating at full capacity. Soft starts would not be required
for infrequently occurring pile restrikes (short duration events with
low blow counts) due to technical conflicts with hammer energy.
Noise Attenuation Systems
A bubble curtain would be deployed for all impact pile driving
except during pile restrikes, regardless of pile size or time of year.
Pile restrikes are short-duration events with low blow counts that
occur infrequently to test pile stability after it has been driven.
Using soft start techniques during restrikes presents technical
conflicts with hammer energy. A 3-ring bubble curtain would be used
during impact pile driving of 96-in and 48-in piles, consisting of
three perforated pipe rings stacked vertically along the length of the
driven pile. The pipes in all layers would be arranged in a geometric
pattern to allow for the pile being driven to be completely enclosed by
bubbles for the full depth of the water column. At a minimum, the
bubble curtain would distribute air bubbles around 100 percent of the
piling circumference for the full depth of the water column, the lowest
bubble ring would be in contact with the substrate for the full
circumference of the ring, and the weights attached to the bottom ring
would ensure 100 percent substrate contact. No parts of the ring or
other objects would prevent full substrate contact. In addition, air
flow to the bubblers would be balanced around the circumference of the
pile.
For vibratory pile driving, a separate perimeter-style bubble
curtain system would be deployed from June 1-September 30 when dolphins
are most likely to be in the area. The perimeter style hose will sit on
the riverbed and surround the pile being driven. The hose will be a
Flexral AR60HT hose perforated with \1/4\-in holes at 5-in spacing or
similar.
Impact hammering associated with the 36-in trestle piles will also
be protected by either a bubble ring system or a perimeter ring system.
Both bubble curtain systems were evaluated for effectiveness during
the fall 2025 FSK Bridge Test Pile Program (table 14) (Denes, 2026).
The effectiveness of the 3-ring bubble curtain was measured during the
installation of eight 96-in piles. During the installation of the first
two test piles, the bubble curtain was turned on and off in
approximately 15-minute intervals. Measurements from the rest of the
piles occurred with the bubble curtain active throughout. To determine
the effectiveness of the bubble curtains, regressions of measurements
of pile driving noise were used to estimate the SPL at approximately 10
m from the pile for each hammer type and bubble curtain condition (on/
off). The average SPL at 10 m for impact pile driving without a bubble
curtain was 206.3 dB re: 1 [mu]Pa and with a bubble curtain was 180.0
re: 1 [mu]Pa.
[[Page 21443]]
Table 14--Measured Bubble Curtain Effectiveness From FSK Test Pile
Program (October 2025)
[Denes, 2026]
------------------------------------------------------------------------
Measured
Method Bubble curtain type attenuation
(dB)
------------------------------------------------------------------------
Impact......................... Tiered 3-ring system... 26.3
Vibratory...................... Perimeter hose system.. 6.0
------------------------------------------------------------------------
During the noise monitoring study, vibratory setting was conducted
for under 10 minutes per pile, an insufficient duration to measure
alternating bubble curtain conditions for a given pile and have the
bubbles dissipate. Therefore, there was only one pile measured with the
bubble curtain off. The average SPL at 10 m for vibratory setting
without a bubble curtain was 174.0 dB re: 1 [mu]Pa RMS and with a
bubble curtain was 168.0 dB re: 1 [mu]Pa RMS (Denes, 2026).
Based on our evaluation of the applicant's proposed measures, NMFS
has preliminarily determined that the proposed mitigation measures
provide the means of effecting the least practicable impact on the
affected species or stocks and their habitat, paying particular
attention to rookeries, mating grounds, and areas of similar
significance. NMFS conducted an independent evaluation of the proposed
measures, and has preliminarily determined for each of the proposed
IHAs that the proposed mitigation measures provide the means of
effecting the least practicable impact on the affected species or
stocks and their habitat, paying particular attention to rookeries,
mating grounds, and areas of similar significance.
Proposed Monitoring and Reporting
In order to issue an IHA for an activity, section 101(a)(5)(D) of
the MMPA states that NMFS must set forth requirements pertaining to the
monitoring and reporting of such taking. The MMPA implementing
regulations at 50 CFR 216.104(a)(13) indicate that requests for
authorizations must include the suggested means of accomplishing the
necessary monitoring and reporting that will result in increased
knowledge of the species and of the level of taking or impacts on
populations of marine mammals that are expected to be present while
conducting the activities. Effective reporting is critical both to
compliance as well as ensuring that the most value is obtained from the
required monitoring.
Monitoring and reporting requirements prescribed by NMFS should
contribute to improved understanding of one or more of the following:
<bullet> Occurrence of marine mammal species or stocks in the area
in which take is anticipated (e.g., presence, abundance, distribution,
density);
<bullet> Nature, scope, or context of likely marine mammal exposure
to potential stressors/impacts (individual or cumulative, acute or
chronic), through better understanding of: (1) action or environment
(e.g., source characterization, propagation, ambient noise); (2)
affected species (e.g., life history, dive patterns); (3) co-occurrence
of marine mammal species with the activity; or (4) biological or
behavioral context of exposure (e.g., age, calving or feeding areas);
<bullet> Individual marine mammal responses (behavioral or
physiological) to acoustic stressors (acute, chronic, or cumulative),
other stressors, or cumulative impacts from multiple stressors;
<bullet> How anticipated responses to stressors impact either: (1)
long-term fitness and survival of individual marine mammals; or (2)
populations, species, or stocks;
<bullet> Effects on marine mammal habitat (e.g., marine mammal prey
species, acoustic habitat, or other important physical components of
marine mammal habitat); and
<bullet> Mitigation and monitoring effectiveness.
The monitoring and reporting requirements described in the
following were proposed by FHWA in its adequate and complete
application and/or are the result of subsequent coordination between
NMFS and FHWA. FHWA has agreed to the requirements. NMFS describes
these below as requirements and has included them in the proposed IHAs.
Visual Monitoring
Qualified NMFS-approved PSOs must conduct monitoring in accordance
with the project's Marine Mammal Monitoring Plan. PSOs would be
independent of the activity contractor (for example, employed by a
subcontractor) and have no other assigned tasks during monitoring
periods. At least one PSO would have prior experience performing the
duties of a PSO during an activity pursuant to a NMFS-issued incidental
take authorization. Other PSOs may substitute other relevant
experience, education (degree in biological science or related field),
or training for prior experience performing the duties of a PSO during
construction activity pursuant to a NMFS-issued ITA. PSOs would be
present during all pile installation and removal activities, including
vibratory and impact methods during summer months, with reduced
presence during spring, fall, and winter seasons, in accordance with
the following:
<bullet> Observer training must be provided before the project
starts and must include instruction on species identification
(sufficient to distinguish the species in the project area),
description and categorization of observed behaviors, and
interpretation of behaviors that may be construed as being reactions to
the specified activity, proper completion of data forms, and other
basic components of biological monitoring, including tracking of
observed animals or groups of animals such that repeat sound exposures
may be attributed to individuals (to the extent possible).
<bullet> All PSOs must have no other project-related tasks while
conducting monitoring.
<bullet> PSOs shall be placed at the best vantage point(s)
practicable to monitor for marine mammals and implement shutdown or
delay procedures when applicable through communication with the
equipment operator.
<bullet> A minimum of two independent NMFS-approved PSOs will be
active and on duty at a time from June 1 through September 30. The PSO
closest to the hammer will be designated as the lead PSO. The lead PSO
will be responsible for monitoring the shutdown zone and coordinating
communication between PSOs and between PSOs and construction crew. One
PSO would be stationed on or near the pile driving platform or barge to
monitor the full shutdown zone and as much of the clearance zone as
possible. Another PSO would be actively monitoring the downriver
portion of the
[[Page 21444]]
clearance zone from the bow of the barge or equivalent.
<bullet> From October 1 through November 30 and March 1 through May
31, one PSO will be active and on duty at a time. This PSO will be
stationed on the pile driving barge or equivalent.
<bullet> From December 1 through February 28, one PSO will be
active and on duty one day a week. This PSO will be stationed on the
pile driving barge or equivalent.
<bullet> Between April 15 and October 30, pile driving activities
will be initiated only during daylight hours when the PSO (if present)
can visually monitor for the presence of marine mammals. In the event
that pile driving continues after dusk (to complete the installation of
a pile in progress), night vision equipment (handheld night vision
devices or handheld thermal imagers), will be used.
<bullet> Monitoring would be conducted 30 minutes before, during,
and 30 minutes after drilling and pile driving/removal activities. In
addition, observers shall record all incidents of marine mammal
occurrence, regardless of distance from activity, and must document any
behavioral reactions in concert with the distance from piles being
driven or removed. PSOs would include the time to install or remove a
single pile or series of piles, as long as the time elapsed between
uses of the pile driving equipment is no more than 30 minutes.
<bullet> PSOs would scan the waters using binoculars and/or the
naked eye to search for marine mammals.
<bullet> PSOs will rotate shifts and stations to reduce potential
fatigue. No PSO will be assigned a combined watch schedule of more than
12 hours in any 24-hour period.
Additionally, PSOs should meet the following qualifications:
<bullet> Have the ability to conduct field observations and collect
data according to assigned protocols;
<bullet> Experience or training in the field identification of
marine mammals, including the identification of behaviors;
<bullet> Sufficient training, orientation, or experience with the
construction operation to provide for personal safety during
observations;
<bullet> Writing skills sufficient to prepare a report of
observations including but not limited to the number and species of
marine mammals observed; dates and times when in-water construction
activities were conducted; dates and times when in-water construction
activities were suspended to avoid potential incidental injury from
construction sound of marine mammals observed within a defined shutdown
zone; and marine mammal behavior; and
<bullet> Ability to communicate orally, by radio, or in person with
project personnel to provide real-time information on marine mammals
observed in the area as necessary.
Hydroacoustic Monitoring--The FHWA would conduct hydroacoustic
monitoring to ground truth the zones over which effects to marine
mammals are expected for each location and source/mitigation system
configuration. An acoustic monitoring plan would be submitted to NMFS
no later than 60 days prior to the beginning of impact pile driving for
approval. FHWA proposes that underwater noise measurements of the first
5 piles installed of each size (24-, 36-, 48-, and 96-in steel) with
both impact and vibratory driving would be collected. Beyond the first
5 piles of each size, underwater noise monitoring will be conducted
during the installation of one pile per month for the duration of the
project under normal production driving conditions.
Data will be collected using a bottom-moored hydrophone at a single
location. Underwater acoustic recorders will be deployed at prescribed
locations in the area of the project at different distances from the
active pile (see figure 14 of the FHWA's application). Underwater noise
data will be collected at near-field, intermediate, and far-field
locations to monitor noise associated with the active pile.
Environmental data would be collected, including but not limited
to, the following: wind speed and direction, air temperature, humidity,
surface water temperature, water depth, wave height, weather
conditions, and other factors that could contribute to influencing the
airborne and underwater sound levels (e.g., aircraft, boats, etc.). The
chief inspector would supply the acoustics specialist with the
substrate composition, hammer model and size, hammer energy settings
and any changes to those settings during the piles being monitored.
For acoustically monitored piles, data from the monitoring
locations would be post-processed to obtain the following sound
measures:
<bullet> Mean, median, minimum, and maximum RMS pressure level in
[dB re 1 [mu]Pa];
<bullet> Mean, median, minimum, and maximum single strike SEL in
[dB re [mu]Pa\2\s];
<bullet> Cumulative SEL as defined by the mean single strike SEL +
10*log10 (number of hammer strikes) in [dB re [mu]Pa\2\s]; and
<bullet> A frequency spectrum (pressure spectral density) in dB re
[mu]Pa\2\ per Hz based on the average of up to eight successive strikes
with similar sound. Spectral resolution would be 1 Hz, and the spectrum
would cover nominal range from 7 Hz to 20 kHz.
Reporting
Draft marine mammal monitoring and hydroacoustic monitoring reports
would be submitted to NMFS within 90 days after the completion of pile
driving activities for each IHA or 60 days before the requested date of
issuance of any future IHAs for projects at the exact location,
whichever comes first. The marine mammal monitoring report would
include an overall description of work completed, a narrative regarding
marine mammal sightings, and associated PSO data sheets. Specifically,
the report must include:
<bullet> Dates and times (beginning and end) of all marine mammal
monitoring;
<bullet> Construction activities occurring during each daily
observation period, including the number and type of holes/piles driven
or removed and by what method (i.e., impact, vibratory, or drilling);
<bullet> PSO locations during marine mammal monitoring; and
<bullet> Environmental conditions during monitoring periods (at the
beginning and end of a PSO shift and whenever conditions change
significantly), including Beaufort sea state and any other relevant
weather conditions, including cloud cover, fog, sun glare, and overall
visibility to the horizon, and estimated observable distance. Upon
observation of a marine mammal, the following information is required:
<bullet> The name of the PSO who sighted the animal(s), the PSO's
location, and activity at the time of the sighting;
<bullet> The time of the sighting;
<bullet> Identification of the animal(s) (e.g., genus/species,
lowest possible taxonomic level, or unidentified), the PSO's confidence
in identification, and the composition of the group if there is a mix
of species;
<bullet> The distance and bearing of each marine mammal observed
relative to the specified activity for each sighting (e.g., if pile
driving was occurring at the time of sighting);
<bullet> The estimated number of animals (min/max/best estimate);
<bullet> The estimated number of animals by cohort (adults,
juveniles, neonates, group composition, sex class, etc.);
<bullet> The animal's closest point of approach and estimated time
spent within the harassment zone;
<bullet> A description of any marine mammal behavioral observations
(e.g.,
[[Page 21445]]
observed behaviors such as feeding or traveling), including an
assessment of behavioral responses thought to have resulted from the
activity (e.g., no response or changes in behavioral state such as
ceasing feeding, changing direction, flushing, or breaching);
<bullet> The number of marine mammals detected within the
harassment zones by species (differentiated by month as appropriate);
<bullet> Detailed information about any implementation of any
mitigation triggered (e.g., shutdowns and delays), a description of
specific actions that ensued, and the resulting changes in the behavior
of the animal(s), if any; and
<bullet> All PSO datasheets and/or raw sighting data in an
electronic tabular format with the draft report.
Acoustic monitoring report(s) must be submitted on the same
schedule as visual monitoring reports (i.e., within 90 days following
the completion of construction). The acoustic monitoring report must
contain the informational elements described in the Acoustic Monitoring
Plan and, at minimum, must include:
<bullet> Hydrophone equipment and methods: (1) recording device,
sampling rate, calibration details, distance (m) from the pile where
recordings were made; and (2) the depth of water and recording
device(s);
<bullet> Location, identifier, orientation (e.g., vertical,
battered), material, and geometry (shape, diameter, thickness, length)
of pile being driven, substrate type, method of driving during
recordings (e.g., hammer model and energy), and total pile driving
duration;
<bullet> Whether a sound attenuation device is used and, if so, a
detailed description of the device used, its distance from the pile and
hydrophone, and the duration of its use per pile;
<bullet> For impact pile driving: (1) number of strikes per day and
per pile and strike rate; (2) depth of substrate to penetrate; (3)
decidecade (one-third octave) band spectra in tabular and figure
formats computed on a per-pulse basis, including the arithmetic mean or
median for all computed spectra; (4) pulse duration and median, mean,
maximum, minimum, and number of samples (where relevant) of the
following sound level metrics: (5) RMS SPL; (6) SEL<INF>24</INF>, Peak
(PK) SPL, and SEL<INF>ss</INF>; and
<bullet> For vibratory driving/removal: (1) duration of driving per
pile; (2) vibratory hammer operating frequency; (3) decidecade (one-
third octave) band spectra in tabular and figure formats for 1-sec
windows, including the arithmetic mean or median for all computed
spectra; and (4) median, mean, maximum, minimum, and number of samples
(where relevant) of the following sound level metrics: 1-sec RMS SPL,
SEL<INF>24</INF> (and timeframe over which the sound is averaged).
If no comments are received from NMFS within 30 days, the draft
reports would constitute the final reports. If comments are received, a
final report addressing NMFS comments must be submitted within 30 days
after receipt of comments.
Reporting Injured or Dead Marine Mammals
In the unanticipated event that the specified activity causes the
take of a marine mammal in a manner prohibited by the IHAs (if issued),
such as an injury, serious injury, or mortality, FHWA must immediately
cease the specified activities and report the incident to the NMFS
Office of Protected Resources (<a href="/cdn-cgi/l/email-protection#4f1f1d61061b1f61022021263b203d2621281d2a3f203d3b3c0f21202e2e61282039"><span class="__cf_email__" data-cfemail="4e1e1c60071a1e60032120273a213c2720291c2b3e213c3a3d0e20212f2f60292138">[email protected]</span></a> and
<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="347d60641a5c5b40575c5f5d5a745a5b55551a535b42">[email protected]</a>) and to the regional stranding coordinator as
soon as feasible. The report must include the following information:
<bullet> Time, date, and location (latitude/longitude) of the first
discovery (and updated location information if known and applicable);
<bullet> Species identification (if known) or description of the
animal(s) involved;
<bullet> Condition of the animal(s) (including carcass condition if
the animal is dead);
<bullet> Observed behaviors of the animal(s), if alive;
<bullet> If available, photographs or video footage of the
animal(s); and
<bullet> General circumstances under which the animal was
discovered.
Activities would not resume until NMFS can review the circumstances
surrounding the prohibited take. NMFS would work with FHWA to determine
what is necessary to minimize the likelihood of further prohibited take
and ensure MMPA compliance. FHWA must not resume in-water construction
activities until NMFS has notified them via letter, email, or
telephone.
If FHWA discovers an injured or dead marine mammal, and the lead
PSO determines that the cause of the injury or death is unknown and the
death is relatively recent (e.g., in less than a moderate state of
decomposition as described in the next paragraph), then the Navy would
immediately report the incident to the NMFS Office of Protected
Resources (<a href="/cdn-cgi/l/email-protection#bcecee92f5e8ec92f1d3d2d5c8d3ced5d2dbeed9ccd3cec8cffcd2d3dddd92dbd3ca"><span class="__cf_email__" data-cfemail="7323215d3a27235d3e1c1d1a071c011a1d142116031c010700331d1c12125d141c05">[email protected]</span></a>) and to the regional
stranding coordinator as soon as feasible. The report would include the
same information identified in the paragraph above. Activities would be
able to continue while NMFS reviews the circumstances of the incident.
NMFS would work with FHWA to determine whether modifications in the
activities are appropriate.
Finally, in the event that FHWA discovers an injured or dead marine
mammal and the lead PSO determines that the injury or death is not
associated with or related to the activities authorized in the IHAs
(e.g., previously wounded animal, carcass with moderate to advanced
decomposition, or scavenger damage), the FHWA would report the incident
to the Office of Protected Resources, NMFS, and the NMFS Stranding
Hotline and/or by email to the Regional Stranding Coordinator, within
24 hours of the discovery. FHWA would provide photographs, video
footage (if available), or other documentation of the stranded animal
sighting to NMFS and the Marine Mammal Stranding Network.
Negligible Impact Analysis and Determination
NMFS has defined negligible impact as an impact resulting from the
specified activity that cannot be reasonably expected to, and is not
reasonably likely to, adversely affect the species or stock through
effects on annual rates of recruitment or survival (50 CFR 216.103). A
negligible impact finding is based on the lack of likely adverse
effects on annual rates of recruitment or survival (i.e., population-
level effects). An estimate of the number of takes alone is not enough
information on which to base an impact determination. In addition to
considering estimates of the number of marine mammals that might be
``taken'' through harassment, NMFS considers other factors, such as the
likely nature of any impacts or responses (e.g., intensity, duration),
the context of any impacts or responses (e.g., critical reproductive
time or location, foraging impacts affecting energetics), as well as
effects on habitat, and the likely effectiveness of the mitigation. We
also assess the number, intensity, and context of estimated takes by
evaluating this information relative to population status. Consistent
with the 1989 preamble for NMFS' implementing regulations (54 FR 40338,
September 29, 1989), the impacts from other past and ongoing
anthropogenic activities are incorporated into this analysis via their
impacts on the baseline (e.g., as reflected in the regulatory status of
the species, population size and growth rate where known, ongoing
sources of human-caused mortality, or ambient noise levels).
[[Page 21446]]
NMFS has identified key factors which may be employed to assess the
level of analysis necessary to conclude whether potential impacts
associated with a specified activity should be considered negligible.
These include, but are not limited to, the type and magnitude of
taking, the amount and importance of the available habitat for the
species or stock that is affected, the duration of the anticipated
effect to the species or stock, and the status of the species or stock.
The potential effects of the specified activities on Tamanend's
bottlenose dolphins are discussed below.
Pile driving associated with the FSK Bridge Rebuild project, as
outlined previously, has the potential to disturb or displace marine
mammals. Specifically, the specified activities may result in take, in
the form of Level B harassment only from underwater sounds generated by
pile driving. Potential takes could occur if dolphins are present in
zones ensonified above the threshold for Level B harassment identified
above while activities are underway.
The FHWA's proposed activities and associated impacts would occur
within a limited, confined area of the stocks' range. The work would
occur in the vicinity of the FSK Bridge Rebuild project site, and sound
from the specified activities would be blocked by the shorelines of the
Patapsco River and Chesapeake Bay. The intensity and duration of take
by Level B harassment would be minimized through use of mitigation
measures described herein. Further, the presence of dolphins in the
area is limited and typically seasonal as animals move through the area
chasing prey associated with changing water temperatures, thereby
reducing the potential for prolonged exposure or behavioral
disturbance. In addition, NMFS does not anticipate that serious injury
or mortality will occur as a result of the FHWA's proposed activity
given the nature of the activity, even in the absence of required
mitigation.
Exposures to elevated sound levels produced during pile driving may
cause behavioral disturbance of some individuals. Behavioral responses
of marine mammals to pile driving at the FSK Bridge Rebuild project
site are expected to be mild, short term, and temporary. Effects on
individuals that are taken by Level B harassment, as enumerated in the
Estimated Take section, on the basis of reports in the literature as
well as monitoring from other similar activities elsewhere, will likely
be limited to reactions such as increased swimming speeds, increased
surfacing time, or decreased foraging if such activity were occurring
(e.g., Ridgway et al., 1997; Nowacek et al., 2007; Thorson and Reyff,
2006; Kendall and Cornick, 2015; Goldbogen et al., 2013b; Blair et al.,
2016; Wisniewska et al., 2018; Piwetz et al., 2021). Marine mammals
within the Level B harassment zones may not show any visual cues that
they are disturbed by activities, or they could become alert, avoid the
area, leave the area, or display other mild responses that are not
visually observable such as exhibiting increased stress levels (e.g.,
Rolland et al., 2012; Lusseau, 2005; Bejder et al., 2006; Rako et al.,
2013; Pirotta et al., 2015; P[eacute]rez-Jorge et al., 2016). They may
also exhibit increased vocalization rates, louder vocalizations,
alterations in the spectral features of vocalizations, or a cessation
of communication signals (Hotchkin and Parks 2013).
Bottlenose dolphins in the region will only be present temporarily
based on seasonal patterns. Thus, individuals present will be exposed
to only transient periods of noise-generating activity as they move
past the project site. Most likely, individual animals will either be
temporarily deterred from swimming past the construction activities and
will pass by when no pile driving is occurring, or will swim through
the area more quickly. Takes may also occur during important foraging
seasons, when anadromous fishes are migrating past the project area and
marine mammals follow. However, the FSK Bridge project area represents
a small portion of available foraging habitat and impacts on dolphin
feeding are expected to be minimal. No marine mammal species or
individuals are known or expected to be resident in the project area,
and impacts are unlikely to be more than temporary and low-intensity.
The activities analyzed here are similar to numerous other coastal
construction activities which have taken place with no known long-term
adverse consequences from behavioral harassment. Any potential
reactions and behavioral changes are expected to subside quickly when
the exposures cease, and therefore, no long-term adverse consequences
are expected (e.g., Graham et al., 2017). While there are no long-term
peer-reviewed studies of marine mammal habitat use in the Patapsco
River, studies from other areas indicate that most marine mammals would
be expected to have responses on the order of hours to days. The
intensity of Level B harassment events will be minimized through use of
mitigation measures described herein, which were not quantitatively
factored into the take estimates. The FHWA will use PSOs stationed
strategically to increase detectability of marine mammals during in-
water construction activities, enabling a high rate of success in
implementation of shutdowns to minimize any likelihood of injury.
Further, given the absence of any important habitat areas within the
estimated harassment zones, we assume that potential takes by Level B
harassment will have an inconsequential short-term effect on
individuals and will not result in population-level impacts.
As stated in the Mitigation section, the FHWA will implement
shutdown zones (table 13). No take by Level A harassment is proposed
for authorization and thus is not expected to adversely impact
individual fitness, let alone annual rates of recruitment or survival
for the affected species or stocks.
Repeated, sequential exposure to pile driving noise over a long
duration could result in more severe impacts to individuals that could
affect a population (via sustained or repeated disruption of important
behaviors such as feeding, resting, traveling, and socializing;
Southall et al., 2007). Alternatively, marine mammals exposed to
repetitious construction sounds may become habituated, desensitized, or
tolerant after initial exposure to these sounds (reviewed by Richardson
et al., 1995; Southall et al., 2007). However, given the relatively low
abundance and generally transitory nature of marine mammals in the
Chesapeake Bay and Patapsco River near the project location compared to
the stock sizes (tables 10 and 11), population-level impacts are not
anticipated. The absence of any important habitat areas in the action
area further decreases the likelihood of population-level impacts.
The FSK Bridge Rebuild project is also not expected to have
significant adverse effects on any marine mammal habitats. The long-
term impact on marine mammals associated with the FSK Bridge Rebuild
project would be a small permanent decrease in low-quality potential
habitat because of the shifted footprint of the bridge. Installation of
in-water piles would be temporary and intermittent, and the increased
footprint of the facilities would destroy only a small amount of low-
quality habitat, which currently experiences high levels of
anthropogenic activity. Impacts to the immediate substrate are
anticipated, but these would be limited to minor, temporary suspension
of sediments, which could impact water quality and visibility for a
short amount of time but which would not be expected to have
[[Page 21447]]
any effects on individual marine mammals. Further, there are no known
biologically important areas near the FSK Bridge project zone that will
be impacted by the FHWA's proposed activities.
Impacts to marine mammal prey species are also expected to be minor
and temporary and to have, at most, short-term effects on foraging of
individual marine mammals and likely no effect on the populations of
marine mammals as a whole. Overall, the area impacted by the FSK Bridge
project is very small compared to the available surrounding habitat and
does not include habitat of particular importance. The most likely
impact to prey would be temporary behavioral avoidance of the immediate
area. During construction activities, it is expected that some fish and
marine mammals would temporarily leave the area of disturbance, thus
impacting marine mammals' foraging opportunities in a limited portion
of their foraging range. But, because of the relatively small area of
the habitat that may be affected and lack of any habitat of particular
importance, the impacts to marine mammal habitat are not expected to
cause significant or long-term negative consequences.
In summary and as described above, the following factors primarily
support our preliminary negligible impact determinations for the
affected stocks of Tamanend's bottlenose dolphins:
<bullet> No takes by mortality or serious injury or by Level A
harassment are anticipated or authorized;
<bullet> Any acoustic impacts to marine mammal habitat from pile
driving are expected to be temporary and minimal;
<bullet> Take will not occur in places and/or times where take
would be more likely to accrue to impacts on reproduction or survival,
such as within habitats critical to recruitment or survival (e.g.,
rookery);
<bullet> The FSK Bridge Rebuild project area represents a very
small portion of the available foraging area for all potentially
impacted marine mammal species and does not contain any habitat of
particular importance;
<bullet> Take will only occur within the Chesapeake Bay and
Patapsco River, which is a limited, confined area of any given stock's
home range;
<bullet> Monitoring reports from similar work have documented
little to no observable effect on individuals of the same species
impacted by the specified activities;
<bullet> The required mitigation measures (i.e., soft starts, pre-
clearance monitoring, shutdown zones, bubble curtains) are expected to
be effective in reducing the effects of the specified activity by
minimizing the numbers of marine mammals exposed to injurious levels of
sound; and
<bullet> The intensity of anticipated takes by Level B harassment
is low for all stocks consisting of, at worst, temporary modifications
in behavior, and would not be of a duration or intensity expected to
result in impacts on reproduction or survival.
Based on the analysis contained herein of the likely effects of the
specified activity on marine mammals and their habitat, and taking into
consideration the implementation of the proposed monitoring and
mitigation measures, NMFS preliminarily finds for each of the proposed
IHAs that the total marine mammal take from the proposed activity will
have a negligible impact on all affected marine mammal species or
stocks.
Small Numbers
As noted previously, only take of small numbers of marine mammals
may be authorized under section 101(a)(5)(A) and (D) of the MMPA for
specified activities other than military readiness activities. The MMPA
does not define small numbers and so, in practice, where estimated
numbers are available, NMFS compares the number of individuals taken to
the most appropriate estimation of abundance of the relevant species or
stock in our determination of whether an authorization is limited to
small numbers of marine mammals. When the predicted number of
individuals to be taken is fewer than one-third of the species or stock
abundance, the take is considered to be of small numbers (see 86 FR
5322, January 19, 2021). Additionally, other qualitative factors may be
considered in the analysis, such as the temporal or spatial scale of
the activities.
For all stocks, the number of takes proposed for authorization is
less than one-third of the best available population abundance estimate
(i.e., no more than 1.9 percent of any stock in year 1, and no more
than 0.9 percent of any stock in year 2; see tables 11 and 12). The
maximum annual number of animals that may be authorized to be taken
from these stocks would be considered small relative to the relevant
stock's abundances even if each estimated take occurred to a new
individual.
Based on the analysis contained herein of the proposed activity
(including the proposed mitigation and monitoring measures) and the
anticipated take of marine mammals, NMFS preliminarily finds for each
of the proposed IHAs that small numbers of marine mammals would be
taken relative to the population size of the affected species or
stocks.
Unmitigable Adverse Impact Analysis and Determination
There are no relevant subsistence uses of the affected marine
mammal stocks or species implicated by this action. Therefore, NMFS has
determined that the total taking of affected species or stocks would
not have an unmitigable adverse impact on the availability of such
species or stocks for taking for subsistence purposes.
Endangered Species Act
Section 7(a)(2) of the ESA of 1973 (16 U.S.C. 1531 et seq.)
requires that each Federal agency ensures that any action it
authorizes, funds, or carries out is not likely to jeopardize the
continued existence of any endangered or threatened species or result
in the destruction or adverse modification of designated critical
habitat. To ensure ESA compliance for the issuance of incidental take
authorizations, NMFS consults internally whenever we propose to
authorize take for ESA-listed species.
No incidental take of ESA-listed species is proposed for
authorization or expected to result from this activity. Therefore, NMFS
has determined that formal consultation under section 7 of the ESA is
not required for this action.
Proposed Authorization
As a result of these preliminary determinations, NMFS proposes to
issue two consecutive IHAs to FHWA for conducting the FSK Bridge
Rebuild project near Baltimore, MD, provided the previously mentioned
mitigation, monitoring, and reporting requirements are incorporated. A
draft of the proposed IHAs can be found at: <a href="https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities">https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities</a>.
Request for Public Comments
We request comment on our analyses, the proposed authorization, and
any other aspect of this notice of proposed IHAs for the proposed FSK
Bridge Rebuild project. We also request comment on the potential
renewal of these proposed IHAs as described in the paragraph below.
Please include with your comments any supporting data or literature
citations to help inform decisions on the request for these IHAs or any
subsequent renewal IHAs.
On a case-by-case basis, NMFS may issue a one-time, 1-year renewal
IHA
[[Page 21448]]
following notice to the public providing an additional 15 days for
public comments when (1) up to another year of identical or nearly
identical activities as described in the Description of Proposed
Activity section of this notice is planned or (2) the activities as
described in the Description of Proposed Activity section of this
notice would not be completed by the time the IHA expires and a renewal
would allow for completion of the activities beyond that described in
the Dates and Duration section of this notice, provided all of the
following conditions are met:
<bullet> A request for renewal is received no later than 60 days
prior to the needed renewal IHA effective date (recognizing that the
renewal IHA expiration date cannot extend beyond 1 year from expiration
of the initial IHA).
<bullet> The request for renewal must include the following:
1. An explanation that the activities to be conducted under the
requested renewal IHA are identical to the activities analyzed under
the initial IHA, are a subset of the activities, or include changes so
minor (e.g., reduction in pile size) that the changes do not affect the
previous analyses, mitigation and monitoring requirements, or take
estimates (with the exception of reducing the type or amount of take).
2. A preliminary monitoring report showing the results of the
required monitoring to date and an explanation showing that the
monitoring results do not indicate impacts of a scale or nature not
previously analyzed or authorized.
<bullet> Upon review of the request for renewal, the status of the
affected species or stocks, and any other pertinent information, NMFS
determines that there are no more than minor changes in the activities,
the mitigation and monitoring measures will remain the same and
appropriate, and the findings in the initial IHA remain valid.
Dated: April 16, 2026.
Kimberly Damon-Randall,
Director, Office of Protected Resources, National Marine Fisheries
Service.
[FR Doc. 2026-07768 Filed 4-21-26; 8:45 am]
BILLING CODE 3510-22-P
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