Recorded salmon data reveal 40 years of marine food web change

Alaskan waters are important fisheries for salmon. Complex marine food webs support these fisheries, and scientists want to know how climate change is reshaping them. But finding past models is not easy.

„We really have to open our minds and get creative about what can serve as an environmental data source,” he said. Natalie MasticHe is currently a postdoctoral researcher at the Peabody Museum of Natural History at Yale University.

As a doctoral student at the University of Washington in Seattle, Mastic studied Alaskan seafood webs using a decidedly unconventional source: old salmon cans. The cans contained fillets of four salmon species caught over a 42-year period in the Gulf of Alaska and Bristol Bay. Mastick and his colleagues dissected preserved fillets from 178 cans and counted the number of anisakid roundworms — a common, tiny marine parasite — inside the meat.

The parasites are killed during the canning process and, if eaten, pose no risk to the human consumer. But counting anisakids is one way to measure how well a marine ecosystem is doing.

„Everyone assumes that worms in your salmon is a sign that things have gone bad,” he said. Chelsea Wood, a UW associate professor of aquatic and fisheries sciences. „But the anisakid life cycle integrates many elements of the food web. I see their presence as a signal that the fish on your plate came from a healthy ecosystem.”

Research Group Reports a Paper Anisakid worm levels increased in chum and pink salmon from 1979 to 2021, and remained the same in coho and sockeye salmon, published April 4 in Environment & Evolution.

„Anisakids have a complex life cycle that requires multiple types of hosts,” said Mastic, who is lead author on the paper. „The fact that we see their numbers rise over time, as we do with pink and chum salmon, indicates that these parasites have been able to find all the right hosts and reproduce. This could indicate a stable or recovering ecosystem with enough right hosts for anisakids.”

The Anisakids begin to live freely in the sea. They enter the food web when they eat small marine vertebrates like krill. As that initial host is eaten by another species, the worms come along for the ride. For example, infected krill may be eaten by a small fish, which in turn is eaten by larger fish such as salmon. This cycle continues until the anisakids arrive in the gut of a marine mammal and reproduce. The eggs are released back into the ocean to hatch and start the cycle again with a new generation.

„If a host is not present — marine mammals, for example — anisakids cannot complete their life cycle and their numbers decline,” said Wood, senior author on the paper.

People cannot serve as hosts to the Anisakids. Eating them in fully cooked fish poses little risk because the worms are dead. But anisakids — also known as „sushi worms” or „sushi parasites” — can cause symptoms similar to food poisoning or a rare condition. Anisakiasis If consumed alive in raw or undercooked fish.

The Seafood Association, a trade group based in Seattle, donated cans of salmon to Wood and his team. The association no longer needs cans set aside each year for quality control purposes. Mastic and co-author Rachel Welicki, an assistant professor at Newman University in Pennsylvania, tested different methods for dissecting canned fillets and searching for anisakids. The worms are about a centimeter (0.4 inch) long and curl up in the fish's muscle. They found that pulling the fillets apart with forceps allowed the team to accurately count worm carcasses with the aid of a dissecting microscope.

There are several explanations for the increase in anisakid levels in pink and chum salmon. Congress passed it in 1972 Marine Mammal Protection ActThis has allowed seals, sea lions, orcas and other marine mammals to recover following population declines.

„Anisakids can only reproduce in the gut of a marine mammal, so this could be an indication that during our study period – 1979 to 2021 – anisakid levels are increasing due to greater opportunities to reproduce,” Mastic said.

Other possible explanations include warming temperatures or the positive impacts of the Clean Water Act, Mastic added.

Consistent anisakid levels in coho and sockeye are difficult to explain because there are dozens of anisakid species, each with its own distinct invertebrate, fish, and mammal hosts. Although the canning process left the hard anisakid exterior intact, it destroyed the soft parts of their anatomy that would allow identification of individual species.

Mastic and Wood believe the approach could be used to look at parasite levels in other canned fish, such as sardines. They also hope the project will help make new, serendipitous connections that could spark further insight into past ecosystems.

„This study came about because people heard about our research through the grapevine,” Wood said. „These insights into past ecosystems can only be gained by networking and making connections to uncover untapped sources of historical data.”

Co-authors on the paper are UW undergraduate Aspen Katla and Bruce Odegard and Virginia Ng with the Seafood Association. This research was supported by the US National Science Foundation, Alfred P. Funding was provided by the Sloan Foundation, the Washington Research Foundation, and the University of Washington.