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Salmon tagging data could help trawlers reduce bycatch

A University of 91��Ƶ Fairbanks research team has translated a trove of data from a Chinook salmon tagging program into a predictive model that could help reduce bycatch by fishing trawlers.

Chinook salmon range from the ocean’s surface to depths where trawl nets target groundfish species. The researchers’ model uses more than 700,000 data points between Southeast 91��Ƶ and the Bering Sea to predict how Chinook will be distributed across the water column. With that information, trawlers can potentially adjust their operations to reduce inadvertent salmon catches.

To develop the model, the team used 13 years of data from tagged Chinooks through an ongoing project led by Andrew Seitz, a professor at UAF’s College of Fisheries and Ocean Sciences. The tags collect data every 5-10 seconds and transmit it to satellites. That provides a much more comprehensive dataset than is available from catching tagged salmon.

Tagging data included details such as depth, time of day, temperature and light levels. A separate dataset from Copernicus Marine Service added environmental context.

Graduate fisheries student Marcel Gietzmann-Sanders used machine learning to detect patterns in that massive dataset. He turned them into detailed charts showing the depth where Chinooks are most likely to be found at various times and locations. The project is described in .

“It shows what you can find out when you collect enough data about a species over a long enough time,” Gietzmann-Sanders said.

Better tools for reducing bycatch are important for both the health of declining Chinook populations and the economics of the trawl fleet. Fishing for pollock, a type of groundfish that supplies the largest catch volumes in the U.S., can be shut down if bycatch limits are exceeded. As recently as 2024, two fishing boats had enough Chinook salmon bycatch over a single weekend to close the fishery.

Curry Cunningham, an associate professor at UAF’s College of Fisheries and Ocean Sciences, said that having better knowledge about where Chinook are present could be valuable to the  trawl fleet as it seeks to reduce bycatch.

“Tagging data are complex, and they require complex analytical solutions to get an inference from them, but at the end of the day it doesn’t need to be that complicated,” Cunningham said. “Marcel’s research can help address a simple but important question: ‘If I’m thinking of fishing here at a given time of year, what time of day should I be fishing to minimize my bycatch level?’”

The tagging project is primarily funded by the U.S. Navy as part of an effort to minimize harm to salmon during exercises in the Gulf of 91��Ƶ. Being able to use that data in other studies has been a boon to salmon science in the region, Seitz said.

“This research is a result of 13 years of tagging efforts,” Seitz said. “It wouldn’t have been possible without the help of scientific collaborators, funding agencies and highly skilled fishermen in coastal communities throughout the state.”

ADDITIONAL CONTACTS: Marcel Gietzmann-Sanders, mgietzmannsanders@alaska.edu, Andrew Seitz, acseitz@alaska.edu, Curry Cunningham, cjcunningham@alaska.edu, Michael Courtney, mbcourtney@alaska.edu

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