Scientists use genetics to track salmon bycatch
Salmon stocks from up and down the Pacific coast congregate in the Gulf of Alaska and the Bering Sea to feed.
That’s also where trawlers go to harvest millions of pounds of pollock and other groundfish. And those trawlers often accidentally scoop up salmon and other fish in their nets, too — a problem known as bycatch.
Scientists with NOAA Fisheries, which oversees federal fisheries in those waters, want to understand where the bycatch is coming from — and where those fish would return to — so that they can understand the impacts of bycatch on specific stocks. That’s especially true for stocks in western Alaska, an area of the state that is seeing dismal salmon returns.
"100 percent, that's our focus for chum, given its overweighted importance to subsistence fisheries," said Wes Larson, a fisheries geneticist with NOAA Fisheries.
His team analyzes and sequences the DNA of salmon samples coming off trawler vessels to estimate what portion of the salmon bycatch is coming from where.
Geneticists have been using that technology for years. But now, Larson said advancements are helping them do that analysis much quicker — which , in turn, could inform more up-to-date decisions from fisheries managers.
Data from NOAA is an important source of information for the North Pacific Fishery Management Council, which manages fishing in Alaska’s federal waters. Many of the trawl vessels that scoop up the most bycatch in Alaska are operating in those federal waters.
And the bycatch issue has generated a lot of concern in Alaska, particularly for the small-boat fishermen who are impacted by decreased salmon stocks.
Last year, the NPFMC took action on halibut bycatch in the Bering Sea, imposing limits on some trawl fleets based on halibut stock abundance. This summer, it passed up a chance to place new rules on trawlers that catch salmon bycatch, instead requesting new analysis from researchers.
Alaska is seeing sharp declines in king salmon stocks across Alaska and chum salmon stocks in western Alaska, in particular, where the species is an important source of food for subsistence fishermen and their families.
Larson said those stocks are a big focus of the genetics program.
"If we use all our data to understand where western Alaska stocks are, then we can help direct the fleet away from those stocks," he said.
In 2021, about 9.4 percent of salmon bycatch came from western Alaska, according to NOAA’s data. The proportion is larger for chinook salmon — chinook from western Alaska usually make up between 40 to 60 percent of the total bycatch.
Previously, that program has taken as long as a year and a half to get genetic results back to biologists. Larson said today, his team is using updated technology and automated analysis tools to get that information into managers’ hands much faster.
Still, Larson said, the answer is not as simple as telling one fleet to stop fishing at one time.
"There’s no easy solution. It’s this really complicated problem of fleet dynamics and different boat types and their ability to move," he said. "The question is really complicated, which is why we’re throwing so much data at it."
There are other factors at play in salmon declines, too. Scientists think a big culprit in some of these population changes is climate change. That was likely the reason for the recent, drastic drop in Pacific cod stocks — another species Larson’s team is monitoring.