The fishermen and women knew something was off with their catch. “At first, it was just a general comment by everybody: ‘The fish, yeah, I didn’t get any big ones this year,’” said Richard Burnham, who has commercially harvested salmon for four decades in the interior Alaska village of Kaltag.
Now, a new study has borne out those observations on a huge scale, documenting body size declines in fish across the entire state of Alaska in four different species of salmon: chinook, sockeye, silver and chum.
Alaska is “the last largely pristine North American salmon-producing region”, the authors write. Yet the size of the Yukon region chinooks – the largest of the four salmon species – has diminished the most, by 10% compared with those caught before 1990.
The bodies of commercially valuable sockeye shrank by 2% statewide, and silver salmon grew 3% physically smaller.
One likely factor, the authors say, is climate crisis-driven changes in the quality or availability of the fishes’ food. A second constant, albeit weak, dynamic was that all four species were smaller when they were competing with larger numbers of a fifth species of Alaska salmon, the hatchery-raised pink.
Hatcheries release 5 billion salmon across the Pacific Rim each year, and an estimated 15% of the fish in the North Pacific Ocean are pinks raised in hatcheries.
Commercial fishermen target the low-value, soft-fleshed pinks in huge numbers, though they are far less-prized as a recreational and subsistence catch, and many anglers consider them a nuisance.
Beyond calculating the degree to which salmon have shrunk, the scientists also measured the impact of that change on people and ecosystems, finding a one-quarter decrease in the number of meals supplied by each chinook salmon, and a similar decline in the amount of nutrients that spawning chinooks carry back to rivers from the ocean.
Curry Cunningham, one of the study’s co-authors and assistant professor at University of Alaska Fairbanks, said he looks through the lens of the state’s commercial fishing industry, in which he grew up participating.
“Every sockeye, on average across the state, is worth about 50 cents less,” he said. “That’s 50 cents less per fish you’re picking out of the net.”
The scientists say their paper adds to a growing body of evidence that hatchery-raised stocks, along with wild pinks, are competing with other species of salmon and could be crowding them out.
The scientists built their paper on a mountain of salmon harvest records collected over a 60-year period by the Alaska department of fish and game. Their database ultimately included 12.5m individual measurements of fish length, from the middle of the eye to the fork of the tail.
The Link LonkSeptember 08, 2020 at 04:30PM
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The mystery of the shrinking fish: Alaska's salmon are getting smaller - The Guardian
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