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Federal Register / Vol. 86, No. 157 / Wednesday, August 18, 2021 / Notices
Several dead whales have been emaciated with moderate to heavy whale lice cyamid loads. Necropsies have been conducted on a subset of whales with additional findings of vessel strike in three whales and entanglement in one whale. In Mexico, 5055 percent of the free-ranging whales observed in the lagoons in winter have been reported as skinny compared to the annual average of 1012 percent skinny whales normally seen. The cause of the UME is as yet undetermined. For more information, please visit: www.fisheries.noaa.gov/
national/marine-life-distress/2019-2020gray-whale-unusual-mortality-eventalong-west-coast-and.
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. Current data indicate that 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
recommended that marine mammals be divided into functional hearing groups based on directly measured or estimated hearing ranges on the basis of available behavioral response data, audiograms derived using auditory evoked potential techniques, anatomical modeling, and other data. Note that no direct measurements of hearing ability have
been successfully completed for mysticetes i.e., low-frequency cetaceans. Subsequently, NMFS 2018
Revision to its Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing Technical Guidance NMFS, 2018
described generalized hearing ranges for these marine mammal hearing groups.
Generalized hearing ranges were chosen based on the approximately 65 decibel dB threshold from the normalized composite audiograms, with the exception for lower limits for lowfrequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall et al., 2007 retained. Marine mammal hearing groups and their associated hearing ranges are provided in Table 2.

TABLE 2MARINE MAMMAL HEARING GROUPS
NMFS, 2018
Generalized hearing range

Hearing group Low-frequency LF cetaceans baleen whales
Mid-frequency MF cetaceans dolphins, toothed whales, beaked whales, bottlenose whales
High-frequency HF cetaceans true porpoises, Kogia, river dolphins, cephalorhynchid, Lagenorhynchus cruciger & L.
australis.
Phocid pinnipeds PW underwater true seals
Otariid pinnipeds OW underwater sea lions and fur seals

7 Hz to 35 kHz.
150 Hz to 160 kHz.
275 Hz to 160 kHz.
50 Hz to 86 kHz.
60 Hz to 39 kHz.

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Represents the generalized hearing range for the entire group as a composite i.e., all species within the group, where individual species hearing ranges are typically not as broad. Generalized hearing range chosen based on 65 dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans Southall et al., 2007 and PW pinniped approximation.

The pinniped functional hearing group was modified from Southall et al.
2007 on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range Hemila et al., 2006; Kastelein et al., 2009; Reichmuth and Holt, 2013.
For more detail concerning these groups and associated frequency ranges, please see NMFS 2018 for a review of available information. Thirteen marine mammal species nine cetacean and four pinniped all phocid species have the reasonable potential to co-occur with the survey activities. Please refer to Table 1. Of the cetacean species that may be present, five are classified as low-frequency cetaceans i.e., all mysticete species, three are classified as mid-frequency cetaceans i.e., all delphinid species, and one is classified as high-frequency cetacean i.e., harbor porpoise.
Potential Effects of Specified Activities on Marine Mammals and Their Habitat Detailed descriptions of the potential effects of similar specified activities
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have been provided in other recent Federal Register notices, including for survey activities using the same methodology and over a similar amount of time, and affecting similar species e.g., 83 FR 29212, June 22, 2018; 84 FR
14200, April 9, 2019; 85 FR 19580, April 7, 2020. Section VII of UAGIs application provides a comprehensive discussion of the potential effects of the survey. We have reviewed UAGIs application and believe it is accurate and complete. No significant new information is available. The effects of underwater noise from UAGIs geophysical survey have the potential to result in behavioral harassment of marine mammals in the vicinity of the action area. The Federal Register notice for the proposed IHA 86 FR 28787; May 28, 2021 included a discussion of the effects of anthropogenic noise on marine mammals, therefore that information is not repeated here; please to the aforementioned notice for that information.
The Estimated Take section includes a quantitative analysis of the number of individuals that are expected to be taken by this activity. The Negligible Impact
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Analysis and Determination section considers the potential effects of the specified activity, the Estimated Take section, and the Mitigation section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and how those impacts on individuals are likely to impact marine mammal species or stocks.
Description of Active Acoustic Sound Sources The notice of proposed IHA provided a brief technical background on sound, on the characteristics of certain sound types, and on metrics used in this proposal inasmuch as the information is relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document.
Please see that document 86 FR 28787;
May 28, 2021 for additional information. For general information on sound and its interaction with the marine environment, please see, e.g., Au and Hastings 2008; Richardson et al.
1995; Urick 1983.

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