Salmon evolving to get smaller due to early season fishing, study suggests

A study has revealed the way salmon caught at different points in time are evolving genetically due to fish-catching activities. Atlantic Salmon, caught when fish are migrating to spawn, are genetically different from their other counterparts elsewhere.

The study on wild salmon in the northern Baltic Sea pointed out that during the early part of the fishing season, fishing activity chiefly targets salmon carrying a "large salmon genetic variant."

The variant guides Atlantic Salmon to grow large and to mature at an older age, an important characteristic for the fishing and viability of Salmon stocks.

The findings are published in the journal Evolutionary Applications.

How was the study done?

Scientists pursued genetic analyses on thousands of wild salmon caught between 1928 and 2020from the northern Baltic Sea region.

Fishers caught salmon with the "large salmon variant" more often in the early than late fishing season.

"This finding suggests that the timing of fishing may cause evolutionary changes in the age and size that Atlantic salmon reach before maturation. Intensive fishing especially in the early fishing season may lead to the 'large salmon variant' becoming rarer and to salmon spawning at a younger age and smaller size," the lead author of the study Antti Miettinen, PhD, from the Faculty of Biological and Environmental Sciences at the University of Helsinki, said in an official statement.

What does it mean?

The evolutionary impact of fishing in fewer large salmon is not good news for the diversity and viability of salmon populations and for fisherswho value large catches.

The results of the study will help humanity understand the way the evolutionary selection pressures induced by human actions, in this case fishing, can affect wild fish populations and their characteristics.

"By analysing the genetics of samples collected across the northern Baltic over many decades, this study shows how human activities could cause evolutionary changes in wild salmon populations," senior researcher and senior author of the study Victoria Pritchard, PhD, from the University of the Highlands and Islands, said in a statement.

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"This study is a fantastic example of using genetic approaches to answer important questions about the conservation and management of biodiversity. The genetic tools designed during this project can be used to monitor the future impacts of fishing regimen changes," Pritchard says.

The research was done together by the University of Helsinki, Natural Resources Institute Finland (Luke), Swedish Agricultural University (SLU) and the University of the Highlands and Islands (UHI).

(With inputs from agencies)