Hearing tests could create solution to fishing's whale issues

A minke whale swims in open ocean.

A project of the National Marine Mammal Foundation (NMMF) in the United States, in collaboration with the Norwegian Defence Research Establishment, aims to measure the frequency range that minke whales can hear.

The research would fill in an information gap and help lessen human disturbance to a wide range of baleen whales. But it involves capturing and temporarily restraining wild whales, a tricky procedure that some animal rights groups say could stress the big cetaceans.

Funding for the research is coming from President’s Subcommittee on Ocean Science and Technology’s Interagency Task Force on Ocean Noise and Marine Life, which consists of multiple agencies including the Office of Naval Research, the Bureau of Energy Management, the National Oceanic and Atmospheric Administration (NOAA), the U.S. Navy Living Marine Resources, and the Marine Mammal Commission.

Dorian Houser, who directs NMMF’s Biologic and Bioacoustic Research Program, will lead the U.S. team. NMMF is an offshoot of the U.S. Navy’s program to use marine mammals – including sea lions, dolphins, and belugas – for military purposes, such as locating underwater mines and detecting underwater saboteurs. It promotes research, education, and conservation, and supports the veterinary care and training of the Navy’s marine mammals.

Whales can be broadly divided into two types: toothed whales and baleen whales. Because of differences in their anatomy and vocalizations, it is presumed that their range of hearing differs, but to what degree is unknown.

The whales have made convenient subjects for auditory evoked potential (AEP) testing. The AEP method, which is also routinely performed on human newborns to test for deafness, is well-suited for subjects who cannot express whether they can or cannot hear a tone. AEP is a type of electroencephalogram signal emanated from the brain due to hearing an acoustical stimulus. In AEPs collected from whales, three sensors attached with suction cups – an active sensor, inverted sensor, and a ground sensor – are attached to the animal, while the AEP equipment is kept dry on land or in a small boat.

“We do have extensive experience with measurements on toothed whales (belugas, dolphins, porpoises, etcetera) now covering hundreds of individuals and the [for AEP] techniques are used daily in our work with dolphins. Toothed whales echolocate and have a broad frequency range of hearing. Minke whales are members of the baleen whales and presumably do not have the same frequency range of hearing or specializations for echolocation. However, no one has ever successfully tested the hearing of a baleen whale, so this is what we are attempting to find out,” Houser said.

According to Houser, “the AEP data should provide us with empirical evidence of what a minke whale hears.”

“Being the first baleen whale to have its hearing measured, this will be used by regulators to inform what other baleen whale audiograms might look like. This information helps regulators understand the frequencies of sound the whales might respond to, as well as how sensitive they are to sound at different frequencies. All of this information is used when trying to determine if a regulated activity in the ocean produces sound at the frequencies and levels where impacts to the whales might be predicted. The information is also intended to be used in the development of auditory weighting functions, which have been used in U.S. regulations for predicting when sound might cause physical impacts to the ear [e.g. temporary loss of hearing, also called temporary threshold shift],” Houser said.

According to the website Discovery of Sound in the Sea,  progress is being made in using improved understanding of whale hearing in conservation efforts that impact the seafood industry:

  • Pingers on gillnets: Worldwide, over 300,000 cetaceans are estimated to be incidentally caught in fishing gear annually. Porpoises are often caught in gillnets. The fine mesh is both difficult to see and to detect by echolocation, and the cetaceans may also become entangled while feeding on the captured fish. To alert cetaceans to the presence of the net, “pingers” emit pulsed, high-frequency sounds. The frequency of the sound has to be set within a range that the cetaceans can hear but outside of what fish can hear. It has also been discovered that different types of cetaceans respond differently to the pingers, while they may also act as a “dinner bell” for seals and sea lions, so that the effectiveness of pingers depends on the local situation and the resident animals.
  • Avoiding longline stripping: In the Gulf of Alaska sablefish longline fishery, sperm whales strip fish from the lines, risking entanglement for a free meal. Acoustic recorders that pick up the high-frequency clicks used by the whales have shown that they are attracted when they hear the sounds of boat engines engaging and disengaging to haul in lines. Modifying the sounds of the vessel or developing acoustic deterrents may help to eliminate the problem.
  • Avoiding ship strikes: On the U.S. East Coast, ship strikes are major cause of mortality for North Atlantic right whales, which inhabit the busy shipping lanes heading into Boston, Massachusetts. By using automatic detection buoys to listen for vocalizations typical of right whales, ships can be alerted to the presence of whales in the area within about 20 minutes from detection.
  • Reducing noise disturbance: A similar effort to track orcas and slow down ships on the sea routes leading to the Port of Vancouver in order to avoid reduce acoustic disturbance from ships is also being undertaken.

Juvenile minke whales are similar in size to the captive adult beluga whales that have already been tested, but the difficulty of catching them has proven a significant barrier for scientists to overcome.

Previous attempts to catch baleen whales alive to conduct the tests have resulted in the whales escaping. Notably, a separate attempt supported by the E&P Sound and Marine Life Joint Industry Program, involving researchers from Denmark and Hawaii, deployed a seine-net four times to catch a minke whale off Iceland, but each time the whale escaped.

Petter Kvadsheim of the Armed Forces Research Institute, who is the project manager on the Norwegian side of the current effort, said he believes a newly contrived capture method will hold the minke whale firmly, without harming it and long enough for scientists to perform the necessary tests.

This summer, and continuing over the next three summers, the research team planned to block off parts of the Vestfjord in the sea off the municipality of Vestvågøy in Norway’s Lofoten archipelago. Whales were captured between two small islands where they pass during their migration.

Once a whale passes between the islands, the entrances are blocked with barrier nets. After a marine mammal veterinarian has observed the whale and made a decision that it is healthy for testing, another net that spans the width of the waterway will be deployed between two boats. This net will be maneuvered to direct the whale to an opening in a circular aquaculture pen. When the whale enters the pen, the opening will be closed.

The net of the pen can then be pulled up under the whale to create a hammock to limit its movement while also keeping it at the surface, so its blowhole is kept above water while the lower body remains submerged. The hearing test is conducted while the whale is in the hammock. After the hearing test is completed, the whale is released back into the fish farm and then back into the basin. The barrier nets to the basin are then opened so the whale can continue its migration.

Distress and dissent

Washington D.C., U.S.A.-based Animal Welfare Institute, which started with a focus on improving conditions for animals used in research and has expanded to cover other areas; NOAH, Norway’s largest NGO for animals; and Whale and Dolphin Conservation (WDC), a U.K.-registered charity that campaigns against keeping whale and dolphins in captivity for entertainment, have objected to the experiment. The three groups are urging Mattilsynet, the Norwegian Food Safety Authority, to revoke its approval of the project.

“This research project is alarming for several reasons,” Siri Martinsen, a veterinarian who heads NOAH, said. “We are very concerned for the welfare of the involved whales, as these circumstances are very likely to cause them stress and may even impact their health. There is a significant risk that the whales will panic once they are trapped, causing them to thrash or flail about, which could lead to serious injuries as they attempt to flee.”

WDC Policy Director Vanesa Tossenberger is concerned that the researchers have proposed using sedation to calm whales who display signs of stress.

“Little is known about sedating or stunning wild cetaceans, and it is therefore rarely attempted. Available data indicate that sedation of baleen whales in the wild could be life-threatening,” Tossenberger said.

AWI Marine Program Director Susan Millward said the project could also pose dangers to the human researchers.

“If a minke whale, even a juvenile, were to respond with great force, it also could be extremely dangerous for the human researchers. Since whale reactions can be unpredictable, we believe that these researchers – particularly those in the water – will be at risk of serious injury. It is simply not worth taking a chance, particularly when existing research already tells us how baleen whales are affected by ocean noise,” Millward said.

Though there is existing behavioral data from observations on how various wild baleen whales have responded to manmade noises, it is possible that whales can hear and are annoyed by sounds, even when they do not show such behaviors. For example, they might not react noticeably to noises they have gotten used to, even if those noises interfere with their ability to communicate, navigate, or find food, according to an Armed Forces Research Institute press release from January 2021.

“We know from previous studies that baleen whales are affected by sonar and seismic [surveys]. They leave the area, stop feeding or change the way they communicate. But to protect whales from noise, we need to know more about what kind of sounds and frequencies they can actually hear,” it stated.

For NOAH’s Martinsen, part of the distrust of the plan’s goals stems from the organizations that are undertaking it.

“These studies are financed by forces that do the kind of activities that we know harm whales,” she said. “So, it feels like they are sort of delaying in asking for more information, and that the proper measures that could be done to take the whales’ interests more into account – they are not being done. And we have seen in Norwegian media that even when asked if these experiments would result in any measures for the whales, they cannot really answer that. The message is simply, ‘We’ll have to get more knowledge.’ So, I think the focus here is, we do have knowledge to do measures to protect whales, but we’re not doing it.”

The “forces” Martinsen refers to are the military, which conducts sonar drills, and is largely funding the current experiment; and the oil and gas industry, which funded the previous attempt off Iceland by the E&P Sound & Marine Life Joint Industry Program.

Even so, Martinsen said there is at least some cause for optimism regarding conservation measures.

“I think definitely around the world, we would see a lot of interest in adjusting human activity to wildlife, but unfortunately, some industries in some countries – and I would say that Norway is among those countries – are not so interested in doing measures. We are doing some measures, but I think in Norway, we do have a problem with putting financial interests first and regard for wildlife and nature second.”

Update: AWI’s Margie Fishman informed SeafoodSource that the project has been suspended with no whales tested. During the four weeks that the project ran this year, three whales swam into the nets. One was released because it was too large, another escaped under the net, and a third was released because it was a humpback. However, the researchers plan to repeat the project next year as the possibility of catching whales in the net was proven.

Photo courtesy of Graeme Snow/Shutterstock


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