Wild salmon are becoming smaller and this may be associated with aquaculture

Wild salmon are becoming smaller and this may be associated with aquaculture

Atlantic salmon in the river Teno in northern Finland. Credit: Panu Orell / Natural Research Institute Finland

Researchers from Finland used genetic methods to find out how fishing for a food source for an aquaculture fish and changes in salmon fishing can be linked to changes in the size of wild salmon.

The study, recently published in the journal Science, showed that the shrinking size of Atlantic salmon in the river Teno in northern Finland may not be due to direct fishing for salmon. Rather, the impacts could stem from an indirect effect: the commercial fishing of one of wild salmon’s favorite foods in the ocean: a small omega-3 rich. fish called solder.

This indirect effect identified in the study focuses on salmon aquaculture. Some of the capelin catch is used as fishmeal for salmon aquaculture food, which suggests that strong harvests and declining capelin volumes may be an indirect way in which salmon aquaculture can affect wild salmon populations.

“That the aquaculture industry has made significant progress in finding alternative protein sources for aquaculture fish feed, and our study suggests that these efforts have not been in vain, as it appears that capelin harvesting may affect wild salmon stocks. Worldwide, 18 million tonnes of wild fish are harvested annually as capelin for livestock feed, so there is still work to be done to further reduce the effects of aquaculture on wild fish stocks, ”says Professor Craig Primmer at the University of Helsinki.

The study links environmental and human impacts with evolutionary changes

“Our previous research had shown that the age at which salmon matured in this river became younger, and consequently the size of spawning salmon also decreased, showing” evolution in action. “Important to demonstrate rapid development was there are also changes in their DNA by a gene that is known to be associated with maturation size and age, “explains Primmer.

“This previous research could not tell us what environmental or human impacts could be associated with the evolutionary changes. To understand this, we had to link the annual changes in the salmon’s DNA variation with annual changes in environmental and human factors. . ” Dr. Yann Czorlich, the first author of the research continues. “We collected literally millions of data points on factors, including annual water temperature, salmon fishing effort, and commercial fishery catches of the fish, salmon eat in the ocean, and compared them with our data on DNA changes in our 40-year time series. “

Changes in salmon fishing affect the size of salmon

In addition to the indirect effect of the capelin harvest, the team also identified a direct effect of the salmon fishery in the creek, but with a twist. “We found that a special type of net, a salmon pond, which accounts for the majority of net catches, catches predominantly smaller fish, although net fishing is often assumed to catch larger fish,” says Jaakko Erkinaro, research professor at the Natural Resources Institute Finland ( Luke). Native knowledge provided an answer to this surprising result: “We discussed with local Sami fishermen who have been fishing with salmon rods for decades, and they explained that compared to other types of nets, salmon rods have a smaller mesh size used later in the season. “low water, which increases the catch of smaller salmon. This probably explains the result,” Erkinaro continues. Stock fishing has declined in recent years, and at the same time the proportion of small, early maturing fish in spawning stocks has increased.

“Our finding that there are different types of fisheries trading in opposite directions at different stages of their life cycle highlights new challenges for salmon management, but also the value of having unique long-term data series at our disposal,” Erkinaro noted.

The research team examined scale samples from salmon over a 40-year period and linked the variation of a gene that determines the salmon’s reproductive age and size, along with the effects of different capture methods. The scale samples used for the study came from a unique long-term scale archive maintained by Luke. The archive holds samples from more than 150,000 salmon individuals collected by trained, volunteer fishermen since the 1970s from the Teno River, one of the most productive salmon rivers in Europe. The scales were used to determine the age structure of salmon population. They were also the source of DNA for genetic analysis.

Breeding farmed fish with wild fish changes the life cycle of wild fish

More information:
Y. Czorlich et al., Rapid development in the life history of salmon caused by direct and indirect effects of fishing, Science (2022). DOI: 10.1126 / science.abg5980. www.science.org/doi/10.1126/science.abg5980

Provided by Natural Resources Institute Finland

Citation: Wild salmon is getting smaller and it may be linked to aquaculture (2022, February 25) retrieved July 18, 2022 from https://phys.org/news/2022-02-wild-salmon-smaller-linked-aquaculture. html

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