Voracious pink salmon thriving at other species' expense, researchers say

Biological oceanographer Sonia Batten experienced her lightbulb moment on the perils of too manysalmonthree years ago, as she prepared a talk on the most important North Pacific seafood you'll never see on a plate:zooplankton.

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. Zooplanktons nourish everything from juvenilesalmonto seabirds to giant whales, but 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 pinksalmon,'' said Batten, of Canada's Marine Biological Association.

Pinksalmonare 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 ofsalmonpopulating the North Pacific since last century.

But an increasing number of marine researchers say the voracious eaters are thriving at the expense of higher-valuesockeyesalmon, seabirds and other species with whom their diet overlaps.

In addition to the flourishing wild populations of pinksalmon, Alaska hatcheries release 1.8 billion pinksalmonfry annually. And hatcheries in Asian countries contribute an additional threebillion-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 state wildlife authorities to reduce hatchery output.

A 2018 study estimated 665 million adultsalmonin the North Pacific. Pinksalmondominated at 67 per cent, followed by chums at 20 per centandsockeyeat 13 per cent.

Salmonabundance since the late 1970s has been enhanced by favourable ocean conditions, but hatcheries account for 15 per centof the pinks, 60 per centof the chums and fourper centof 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 $120 million 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 program has been successful and continues to provide benefit to Alaskans,'' said Bill Templin, chief fisheries scientist for the Alaska Department of Fish and Game.

Slim pickings

But scientists who don't have a connection to the department take a different view.

Alan Springer, professor emeritus at the Marine Science Institute at the University of Alaska Fairbanks, sees detrimental effects in seabirds whose diets overlap with pinksalmon.

"There's a finite amount of what they eat out there,'' he said.

Zooplankton nourish everything from juvenilesalmonto seabirds to giant whales.

Springer co-wrote a 2014 paper published in the Proceedings of the National Academy of Sciences that noted reproduction of tufted puffins and kittiwakes nosedives in years of pinksalmonabundance.

A 2018 paper in the same journal linked years of abundant pinksalmonwith mass mortalities of short-tailed shearwaters.

"We looked for other potential drivers in the environment,'' Springer said. "We couldn't find any.''

Competition among salmon species

Greg Ruggerone, president of Natural Resources Consultants in Seattle, began analyzing pinksalmoninteractions withsockeyesalmonin 2009 when thesockeyepopulation collapsed in British Columbia's Fraser River.Sockeyereturns fell when pinksalmonwere abundant, he said, and thesockeyewere almost half a kilogramsmaller in those years.

The results, Ruggerone said, suggest "there is this link betweensockeyesalmonand pinksalmonrelated to competition for food.''

A University of Washington study published in Nature Ecology & Evolution concluded that climate warming is creating favourable conditions forsockeyeleaving in freshwater for Alaska's Bristol Bay, allowing them to grow faster in lakes and leave for the ocean after one year instead of two, said lead author Timothy Cline.

However, competition from wild and hatcherysalmon both pinks and chums released by Japandelayedsockeyematuration and kept them in saltwater an extra year.

"There's pretty consistent evidence coming out in the last decade that we are at or near that carrying capacity and it's starting to have impacts on growth and survival ofsalmonall over,'' he said.

Alaska won't reduce hatchery output

The state of Alaska is nearing the end of a 12-year study looking at the proportions of hatchery fish that swim into streams, said Templin, chief fisheries scientist.

The state is not studying whether hatchery pinksalmonare thriving at the expense ofsockeye, chinooksalmon, seabirds or other ocean residents, he said, noting that correlations do not indicate causes.

Changing ocean conditions may affect various species differently and make one of them better able to survive, Templin said. He's not ready to recommend a reduction in hatchery output because of the economic, societal and cultural value of hatchery fish.

Ruggerone would like to see rigorous debate on the pros and cons of releasing billions of hatcherysalmon, especially pinks.

"There's really no other species in the ocean that we are aware of that we have data that can explain these biennial patterns that we see,'' he said.

If it's not pinksalmoncausing problems in other species, Springer said, state scientists should suggest what is.

"We're not making this stuff up,'' he added.