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UAF, trawlers team up to reduce killer whale entanglements

Following a recent spike in Bering Sea killer whale entanglements, a simple addition to fishing nets has delivered positive early results for keeping the big marine mammals out of deep-water flatfish trawls.

The net modification was developed through a collaboration between University of Alaska �Ļ�ӰԺ researcher Hannah Myers and the Alaska Seafood Cooperative, which coordinates a fleet that targets groundfish such as flounder and sole.

Captains working the summer fishery began noticing significantly more killer whale activity around their nets starting in about 2020, which was followed by a sudden rise in entanglements in 2023.

The cooperative, which currently manages 14 catcher-processor vessels in the fishery, reached out to researchers at the UAF College of Fisheries and Ocean Sciences in 2022 for help understanding how the whales behaved around the vessels.

It’s unclear why the increase in interactions happened suddenly, but it became apparent that killer whale pods had identified deep-water flatfish trawl nets as a good place to grab a meal in the Bering Sea. Audio sensors positioned on the fleet’s nets confirmed that killer whales had a heavy presence around the trawl nets, which fish along the ocean floor 400 meters deep.

“There’s a huge interplay of factors that I think we’d all like to understand better, but our theory is they’re probably feeding around the net a lot more than they used to,” said Myers, an assistant professor of fisheries at CFOS. “They’re taking advantage of this incredibly easy food resource.”

The fleet had a particularly rough summer in 2023, with six killer whale deaths and another serious injury. Recognizing the growing problem, a captain in the fleet worked with a gear manufacturer to develop a modification that would deter whales from entering the net. While traditional “excluder devices” allow nontarget species to escape, this was designed to prevent killer whales from entering the net to begin with by placing a large mesh panel at the trawl mouth.

After a successful but limited trial run in 2023, the modified gear was refined for both the 2024 and 2025 seasons, with the new designs tested at a massive flume tank at Memorial University in Newfoundland, Canada. Myers provided expertise in killer whale behavior and biology during the process, while industry personnel ensured the design was practical for their operations.

The updated Bering Sea deep-water flatfish trawl gear, which included a modification known as the “killer whale fence,” was used fleetwide in 2024 for the first time, with a single entanglement recorded during that summer season. The fleet’s 2025 season recently ended without any mortalities.

"We're obviously encouraged by what we see so far," Myers said. "We think it's working because we're not eliminating access to food around the net. We just want to keep them from entering the net, which is the riskiest behavior." 

Sarah Webster, the science projects director for the Alaska Seafood Cooperative, said the project has been a great example of a productive partnership between scientists and fishermen.

“Our collaboration with Dr. Myers was essential to the success of addressing this challenge,” she said. “Her insights into how killer whales were behaving around our vessels really helped us understand what was happening and to fine-tune the gear modification.”

The multiyear project was funded by the Alaska Seafood Cooperative, the Pollock Conservation Cooperative Research Center, the Protected Resources Division in the Alaska regional office of the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service, and the NOAA Fisheries Bycatch Reduction Engineering Program.

ADDITIONAL CONTACT: Hannah Myers, hannah.myers@alaska.edu

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