Scientists warn of too many pink salmon in North Pacific
Marine researchers say pink salmon are thriving at the expense of higher-value sockeye salmon. (File photo of sockeye salmon spawning in Twizel).
Biological oceanographer Sonia Batten experienced her lightbulb moment on the perils of too many salmon three years ago as she prepared a talk on the most important North Pacific seafood you’ll never see on a plate – zooplankton.
Zooplanktons nourish everything from juvenile salmon to seabirds to giant whales.
But as Batten examined 15 years of data collected by instruments on container ships near the Aleutian Islands, she noticed a trend: zooplankton was abundant in even-number years and less abundant in odd-number years.
Something was stripping a basic building block in the food web every other year. And just one predator fit that profile.
“The only thing that we have in this whole area with an up and down, alternating-year pattern is pink salmon,” said Batten of Canada’s Marine Biological Association.
Pink salmon are wildly abundant in odd-number years and less abundant in even-number years. They comprise nearly 70 per cent of what’s now the largest number of salmon populating the North Pacific since last century.
But an increasing number of marine researchers say the voracious eaters are thriving at the expense of higher-value sockeye salmon, seabirds and other species with whom their diet overlaps.
In addition to the flourishing wild populations of pink salmon, Alaska hatcheries release 1.8 billion pink salmon fry annually. And hatcheries in Asian countries contribute an additional 3 billion-plus fish.
“We’re putting too many mouths to compete with the wild fish out there,” says Nancy Hillstrand, owner of a fish processing company near Homer, Alaska, who has been lobbying Alaska wildlife authorities to reduce hatchery output.
A 2018 study estimated 665 million adult salmon in the North Pacific. Pink salmon dominated at 67 per cent, followed by chums at 20 per cent and sockeye at 13 per cent.
Salmon abundance since the late 1970s has been enhanced by favourable ocean conditions but hatcheries account for 15 per cent of the pinks, 60 per cent of the chums and 4 per cent of the sockeyes.
State regulators say they have no evidence that the ocean has reached its carrying capacity for hatchery fish, which rewarded Alaska commercial fishermen with sales averaging US$120 million (NZ$185m) for 2012 through 2017.
They are loath to seek a reduction in hatchery output because of the economic, societal and cultural value of the fish.
“The programme has been successful and continues to provide benefit to Alaskans,” said Bill Templin, chief fisheries scientist for the Alaska Department of Fish and Game.
But scientists who don’t have a connection to the department take a different view.
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