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Fishing Caused Evolution Of Smaller Alaskan Salmon

by the Fish Site Editor
09 June 2011, at 1:00am

US - Research undertaken by University of Washington graduate, Neala Kendall, has discovered how evolution induced by fishing may explain why the bodies of Alaska's sockeye salmon have shrunk by fiveper cent since the 1940s.

NewScientist magazine has published a report of Ms Kendall's findings on their website.

NewScientist states how Ms Kendall used data from canneries on the size and age at maturation of the sockeye salmon fished from five fisheries in Bristol bay, Alaska, since 1943.

The data showed that the fish had become, on average, 14 millimetres shorter. Moreover, the number of fish that spent two rather than three years in the ocean before returning to fresh water to spawn increased by 16 per cent.

Ms Kendall reveals the most likely reason for this decrease in size is down to selective fishing of the largest sockeyes.

Many of the larger fish are breeding females and therefore by removing them, their eggs are also lost. The loss of these eggs has therefore meant that the genes for the heritable large size trait has, or will not, be passed on.

These findings can also be applied to explaining why the population of Atlantic cod in the southern Gulf of St Lawrence has been unable to rebound since the fisheries there collapsed almost three decades ago. As with sockeye, cod fishers harvested the largest fish, including breeding females.

It is predicted that if current trends continue, the lucrative Bristol bay sockeye industry, which brought in $5 billion between 1950 and 2008, could become less profitable.

NewScientist notes that, even without proof of fishing-induced genetic changes, other salmon fisheries in Alaska have begun trying to prevent such problems.

Until recently, most fishers along Alaska's Yukon river caught Chinook salmon, the largest salmon breed, using gill nets designed to catch only the very largest fish – those with a girth greater than 215 millimetres.

Last year, the Alaska Department of Fish and Game mandated a change of design to avoid these large fish and net only those that are 190 millimetres or less.

Those changes may have come too late, says Chris Stark, a fisheries biologist at the University of Alaska in Fairbanks. "The fish have already shrunk so much that 190 millimetres "has become the optimal size for catching big Chinooks", he says. Ms Kendall presented her findings at the second International Marine Conservation Congress in Victoria, British Columbia, Canada, last month.

the Fish Site Editor

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