Scientists who study Pacific salmon abundance and the influence of pink salmon runs on the ocean's food web say 2020's record-low catch and abundance of the five major salmon species in the North Pacific Ocean could signal the beginning of a new reality caused by a warming ocean, which generally benefits pink salmon.
"We hypothesize that a tipping point was reached in the North Pacific Ocean, leading to the substantial decline of all five species of Pacific salmon in 2020. We infer that the tipping point was caused by the combined effects of unusually frequent marine heatwaves since 2014 and exceptional back-to-back year abundances of pink salmon in 2018/2019," Greg Ruggerone and his colleagues, Jim Irvine and Brendan Connors of the Department of Fisheries and Oceans Canada, wrote in an abstract following Ruggerone's keynote speech at the international North Pacific Anadromous Fish Commission conference in May.
Ruggerone is a salmon scientist, vice president of Natural Resources Consultants in Seattle, and a former chair of both the Columbia River Independent Scientific Advisory Board and the Independent Scientific Review Panel.
He noted that 2020 brought the largest decline in Pacific salmon catch since 1930. "While COVID could have impacted commercial fishing in some areas, low harvests in 2020 were largely related to low run sizes, especially in Alaska and Russia," he said in his keynote speech. In an interview, he told California Energy Markets that other evidence indicates that the reduced catch is the result of lower abundance. Insufficient broodstock returned to some hatcheries in Alaska, and many fisheries that did take place were simply unsuccessful, he said.
A preliminary estimate of Pacific Ocean abundance based on commercial salmon catches in Canada, Japan, Korea, Russia and the U.S. indicates that the major salmon species all experienced a crash in 2020 following two record years for pink salmon.
Total salmon catch in the North Pacific was estimated at 322.5 million fish, or 606.7 thousand metric tons—the lowest since 1982. It compares with a 2019 total catch of 563.3 million fish, or 968.7 thousand metric tons. Last year's catch of Chinook salmon saw a 54-percent decline relative to the average for the previous 10 years—the lowest catch since record-keeping began in 1925. Chum salmon declined by 42 percent, pink salmon by 40 percent, coho by 27 percent and sockeye by 10 percent, with declines in most areas offset by a robust sockeye catch in Bristol Bay, Ruggerone said.
The total North American catch in 2020 was nearly 253,000 metric tons—the lowest since 1977, the commission noted. In Washington, Oregon and California—where Chinook, chum and coho are generally the most abundant—2020 saw the lowest total catches of salmon in the commission's database, at 4,500 metric tons.
The hypothesis that a tipping point might have been reached comes in part from a growing body of research pointing to the negative influence of pink salmon on other salmon species. "This finding is consistent with the trophic cascade caused by abundant pink salmon and other studies indicating adverse effects of pink salmon on the growth, age-at-maturation, survival, and abundance of sockeye, Chinook, coho, and chum salmon, marine fishes, seabirds, and potentially southern resident killer whales," the scientists wrote.
Ruggerone said the low salmon abundance levels come after two record years of pink salmon abundance—2018 and 2019—when a combined 1.34 billion adult pink salmon returned to spawning areas or were caught, accounting for about 74 percent of all salmon in the North Pacific Ocean those two years.
The all-time record high number of 700 million pink salmon in 2018 was especially unusual because pinks—which spend one year in the ocean before returning to fresh water—are generally much more abundant in odd-numbered years, with many fewer pinks returning in even-numbered years. Scientists are uncertain why pink salmon saw record returns in 2018, with most returning to Russia, Ruggerone said.
In most years—including even-numbered years—pink salmon represent the majority of the total catch, including last year, when they made up 46 percent of the total catch by weight. That was followed by chum, with 27 percent of the total weight; sockeye, with 23 percent of the weight; and coho, with 3 percent of the weight. Chinook and steelhead each constitute less than 1 percent of the total catch by weight.
While pink salmon have long been dominant, the warming ocean has benefited them. Ruggerone said their numbers began to increase dramatically after the 1977 regime shift in the ocean, which was likely brought on by warming temperatures. "But suddenly, in 2020, the conditions were not good for pink salmon or anything else. It's an interesting observation," Ruggerone said. "What's going to happen this year, in 2021, we don't attempt to forecast."
But the possibility that a tipping point has been reached lends urgency to the need for international coordination, especially on hatchery production, he said. "We think of Alaska as being this place of wild salmon, but they produce the most hatchery salmon by far in North America, and the most pink salmon anywhere," he said. "In Alaska, they have pristine habitat, yet they're adding hatchery fish on top of an abundance of wild salmon. Initially, the hatchery program in Alaska was constructed to fill in the down periods, the years with low salmon numbers."
Ruggerone said that although most pink salmon are from wild runs, significant numbers are produced in hatcheries. From 2005 to 2015, the artificial production of 82 million adult pink salmon per year was about equal to the number of wild sockeye salmon returning from the North Pacific Ocean, and has greatly exceeded both the number of wild chum salmon returning from the ocean and the total abundance of Chinook, he noted.
Their impact on other species is not limited to areas where hatchery pink salmon are released, Ruggerone noted. According to a genetic study published in the Canadian Journal of Fisheries and Aquatic Sciences in January 2013, between 11 and 38 percent of the Chinook sampled on the eastern Bering Sea shelf in the summer period from 2005 to 2011 originated from the West Coast, including the Columbia River.
"With the limited capacity of the ocean to support these highly valuable species—like sockeye and Chinook—why should we be producing so many hatchery pinks that travel long distances at sea and compete with distant salmon stocks, especially when abundance of wild pink salmon is so high?" Ruggerone wondered.