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Drowned Out, Part 1: Vessel Noise and the Marine Mammal Protection Act

Marissa Grenon Gutierrez


  • Discusses how the Marine Mammal Protection Act falls short in reaching chronic and cumulative ocean noises emitted at low frequencies from various sources and sectors.
  • Addresses the pervasive problem of vessel noise in the oceans as underwater noise can cause physiological injury, commonly referred to as a permanent threshold shift in acoustic capacity.
  • Examines the Marine Mammal Protection Act as it relates to the issue of vessel noise.
Drowned Out, Part 1: Vessel Noise and the Marine Mammal Protection Act
Philip Thurston via Getty Images

“Undersea noise pollution is like the death of a thousand cuts.” —Dr. Sylvia Earle

Ambient ocean noise levels have doubled in intensity every 10 years over the last several decades in a trend experts attribute primarily to increasing commercial ship traffic. Although anthropogenic ocean noise pollution affects many marine species, cetaceans are particularly vulnerable given their reliance on acoustic signals for communication, navigation, predator evasion, and feeding. In U.S. waters, the Marine Mammal Protection Act (MMPA), 16 U.S.C. § 1361, et. seq., has become an effective tool at regulating acute sources of anthropogenic ocean noise pollution. See, e.g., Natural Resources Defense Council v. Pritzker, 828 F.3d 1125 (9th Cir. 2016). However, the MMPA falls short in reaching chronic and cumulative ocean noises emitted at low frequencies from various sources and sectors—the most significant of which is noise from commercial shipping vessels.

To date, it appears that the National Marine Fisheries Service (NMFS) has not found vessel noise to arise to a “take” by harassment of marine mammals under the MMPA. However, a recent case may force NMFS to reconsider this position. In Cook Inletkeeper v. Raimondo, Judge Sharon Gleason held that NMFS’s determination that noise from two tugboats towing a drill rig through beluga whale critical habitat would not cause any take by harassment of the whales was arbitrary and capricious. Cook Inletkeeper v. Raimondo, 533 F. Supp. 3d 739, 759 (D. Alaska 2021). The court granted summary judgment in part to plaintiffs, finding that NMFS had failed to take a “hard look” at the impact of noise from tugboat operations on the endangered population of beluga whales. Id. at 768. Under remand consistent with the court’s holding, it is possible that NMFS will amend the incidental take regulation to include takes from vessel noise.

The Problem of Vessel Noise

Ship noise is a pervasive problem. Vessels produce constant, low-frequency noise while operating, primarily from propeller cavitation, with main energy in the 5 to 300 Hertz (Hz) frequency range. Vessel noise typically dominates the ocean soundscape for frequencies between 20 and 300 Hz. Sound levels from cavitation typically range in intensity from about 140 to 195 decibels (dB), depending on factors such as ship type, load, and speed, as well as hull and propeller design. 86 Fed. Reg. 33,670 (June 25, 2021). Additional noise is contributed by engines, gears, and onboard machinery. Because ambient vessel noise is correlated with both the number and size of ships within an area, the modern trend toward more and bigger ships is worsening the problem.

Impacts of anthropogenic noise pollution vary by species. At the most severe end of the spectrum, underwater noise can cause physiological injury, commonly referred to as a permanent threshold shift (PTS) in acoustic capacity. Less severe impacts include temporary threshold shifts (TTS) and behavioral changes to avoid the noise—such as abandonment of a formerly preferred feeding spot. Another common impact is “masking”—a phenomenon that occurs when the frequency of noise blocks the “channel” at which a group of animals typically communicates and relies on for feeding, sheltering, and predator avoidance. Masking is “more likely to occur in the presence of broadband, relatively continuous noise sources such as vessels.” 85 Fed. Reg. 33,913, 33,943 (June 2, 2020). Individuals of some cetacean species have been shown to respond to anthropogenic noise masking by changing their vocalization frequency and intensity—a behavioral response that requires energy expenditure, potentially impacting fitness by increasing metabolic rate and oxygen consumption. Id. at 33,942.

For Cook Inlet beluga whales, noise comprises a high-risk threat that is increasing. Recovery plan for the Cook Inlet beluga whale (Delphinapterus leucas) at xiii, III-3. Yet unlike other high-risk threats, such as natural disasters, chronic anthropogenic noise exposure is controllable. Moreover, the effects of multiple stressors, including underwater noise, are additive and cumulative. Id at III-8 (“[T]he additive effects of multiple noise sources, as well as the combination of noise and other stressors, are of particular concern.”); id at III-30 (“Exposure to any given stressor at a sub-lethal level may predispose individual belugas to greater susceptibility to mortality or long-term effects (for example, reproductive failure) from other stressors”).

Ocean Noise and the Marine Mammal Protection Act

The MMPA was enacted with the purpose of protecting marine mammals from the impacts of human activities. 16 U.S.C. § 1361(1), (6). Its key mechanism is a moratorium on the “taking” of marine mammals, with narrow exceptions that may be permitted by the Secretary of Commerce (acting through NMFS). One such exception is incidental take. Section 101(a)(5) of the MMPA authorizes the secretary to permit the unintentional taking of “small numbers” of marine mammals incidental to an activity within a “specified geographical region” for up to five years at a time if he or she finds that the total of such taking will have a “negligible impact” on the species or stock in question. Id. at § 1371(a)(5)(A)(i). When authorizing incidental take, the secretary must prescribe regulations subject to notice and comment that set forth the “permissible means of taking” and other means of ensuring the “least practicable adverse impact” on the species or stock and its habitat (i.e., mitigation measures), along with requirements for monitoring and reporting such taking. Id. at § 1371(a)(5)(A)(i)(II).

The term “take” is broadly defined by the MMPA to include harassment. Id. at § 1362(13). Harassment is categorized as Level A, which “has the potential to injure a marine mammal or marine mammal stock in the wild” or Level B, which “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.” Id. at § 1362(18)(A); 50 C.F.R. § 216.3.

The National Oceanic and Atmospheric Administration (NOAA) has acknowledged that noise may constitute a take by harassment. In its Interim Sound Threshold Guidance, NOAA provides thresholds of 180 and 190 decibels (dB) for the onset of acoustic injury to cetaceans and pinnipeds, respectively (Level A harassment). The interim guidance also establishes thresholds for the onset of behavioral (Level B) harassment of all marine mammals of 120 and 160 dB for continuous (i.e., non-pulse, such as vessel noise) and impulsive sources, respectively. However, no threshold for behavioral impacts is presented in NOAA’s Marine Mammal Acoustic Technical Guidance, which focuses only on physical injury. Moreover, this guidance is neither binding on the agency nor enforceable against regulated parties—it merely expresses the agency’s current practices in evaluating what noise levels may constitute a “take” by harassment.

Cook Inletkeeper v. Raimondo, 533 F. Supp. 3d 739 (D. Alaska 2021)

In Cook Inletkeeper v. Raimondo, two NGOs, Cook Inletkeeper and Center for Biological Diversity, filed suit in the U.S. District Court for the District of Alaska challenging NMFS’s issuance of an incidental take regulation (ITR) under the MMPA that would authorize Hilcorp Alaska, LLC (Hilcorp) to take marine mammals while conducting oil and gas exploration and production activities in Cook Inlet from 2019 to 2024. Hilcorp sought to conduct seismic exploration throughout Cook Inlet and drill exploratory and development wells using a drill rig that would be towed by tugboats through beluga whale critical habitat without mitigation measures. Cook Inletkeeper, 533 F. Supp. 3d at 758. In the final ITR, NMFS acknowledged that some marine mammals might receive sound levels exceeding 120 dB from the tugs. See 84 Fed. Reg. 12,330, 12,334 (Apr. 1, 2019). However, NMFS concluded that a take was “unlikely to occur” given the “predictable movement” of the vessels, further asserting that “any beluga whales present are likely habituated to the existing baseline of commercial ship traffic.” Id.

Plaintiffs argued that the tugboats would generate significant levels of underwater noise that NMFS disregarded in the ITR. They cited NMFS’s own Recovery Plan for Cook Inlet beluga whales, which identified noise from tugboats as a major threat to beluga whales, and noted that Hilcorp itself estimated in its application that it would take 15 belugas by Level B harassment. Cook Inletkeeper, 533 F. Supp. 3d 754 (citing Petition for Incidental Take Regulations at 85). The court sided with plaintiffs, finding that NMFS’s justification for ignoring tugboat noise as a potential source of take “merely provides conclusions without explaining how those conclusions were reached[,]”Cook Inletkeeper, 533 F. Supp. 3d at 756, and vacated and remanded the ITR. Cook Inletkeeper v. Raimondo, 2021 WL 2169476, at *6–*7 (D. Alaska May 27, 2021).

Judge Gleason’s decision could have ripple effects far beyond Cook Inlet, Alaska; its significance lies in the court’s acknowledgment that vessel noise can rise to the level of a take. It remains unseen whether this case indicates the potential for increased protection of marine mammals from undersea noise, or if regulation of vessel noise will continue to be drowned out by statutory and pragmatic constraints. Next month, the Marine Resources Committee will publish the second part of this article, which examines how the federal government might leverage existing statutory authorities to regulate vessel noise.