U.S. and Canadian scientists are calling for international cooperation over hatchery releases after completing a study that found sockeye runs from Alaska to British Columbia are affected by competition with about a billion pink salmon released from Alaska's hatcheries each year.
Their study looks at the combined effects of ocean warming and increasing competition from pink salmon on 47 sockeye runs across their range.
Although the study doesn't include Columbia River sockeye, the scientists say it is one more piece of evidence showing that the growing dominance by pink salmon in the Pacific Ocean—further boosted by hatcheries—is impacting the growth, maturity and survival of other salmon species.
Yet some jurisdictions—including Alaska and Russia—continue to increase the production of pink and chum salmon with minimal consideration of the impact it has on declining populations of other salmon species, which are often from distant regions.
The study, "Climate and competition influence sockeye salmon population dynamics across the Northeast Pacific Ocean," was published May 26 in the Canadian Journal of Fisheries and Aquatic Sciences.
Pink salmon are already at a competitive advantage. They migrate early to the ocean, have high consumption rates, eat many of the same foods as other salmon and grow quickly during their one-year stay in the ocean.
Their numbers are on the rise. A 2005 study, "Evidence for competitive dominance of Pink salmon (Oncorhynchus gorbuscha) over other Salmonids in the North Pacific Ocean," notes that the number of pink salmon in the North Pacific Ocean has more than doubled since the 1950s. From 1951 through 1976, pink salmon abundance averaged 156 million per year. That increased to 323 million fish per year from 1977 through 2001. From 2005 to 2015, pink salmon represented nearly 70 percent of all Pacific salmon returning from the North Pacific.
The new study takes a look at the specific impact on sockeye of pink salmon raised by hatcheries, which comprise about 17 percent of the total pink salmon population. Although wild salmon make up a majority of the total pink salmon population, the study found that the 82 million adult pink salmon produced by hatcheries each year from 2005 to 2015 reduced the productivity of sockeye in the southern part of their range by an average of 15 percent. The findings help explain why sockeye salmon are faring so poorly in the southern portion of their range.
"Our finding that industrial hatchery production of salmon in some regions may negatively impact salmon from other regions highlights the importance of international cooperation among nations to consider and potentially constrain the number of hatchery salmon released into the ocean," Brendan Connors, a lead author of the study and a research biologist with Fisheries and Oceans Canada, said in a news release from the National Center for Ecological Analysis and Synthesis.
Calls for such cooperation have been being made for decades, he added.
The study was funded by the State of Alaska Salmon and People Project, a partnership between the NCEAS and Anchorage-based Nautilus Impact Investing. Other scientists involved in the study are from NOAA Fisheries, the University of Alaska and the Prince William Sound Science Center.
The findings cannotbe directly translated to Columbia River sockeye populations, since those fish enter the sea in a different region, and probably do not migrate as far north as Fraser River or other B.C. sockeye, Greg Ruggerone, vice president of Natural Resources Consultants and co-author of the study, told NW Fishletter. But other studies link reduced Columbia River salmon survival to competition with pink salmon, Ruggerone said.
Because pink salmon have large runs in odd years followed by much smaller runs in even years, strong differences between even and odd year returns are strongly correlated to impacts from pink salmon. No pink salmon are produced along the Washington or Oregon coasts, yet a 2005 analysis of Columbia River chum abundance found a 50 percent drop in survival during even-numbered years compared to odd-numbered years from 1960 to 2000, he noted.
"Our work contributes to a growing body of evidence that increasing abundances of salmon across the North Pacific, and in particular pink salmon, are linked to a trophic cascade resulting in fewer zooplankton, reduced growth, survival and delayed maturation of salmon and other marine fishes, reduced reproductive success of seabirds, and perhaps even reduced foraging efficiency of southern resident killer whales," Ruggerone said in the news release.
Also a member of NOAA's Hatchery Scientific Review Group, Ruggerone said the State of Alaska requires hatcheries to manage with a precautionary approach with regard to protecting wild salmon from impacts of hatchery fish.
The new study is significant partly because it splits out the specific impact of pink salmon from hatcheries—which has been increasing along with wild salmon. Ruggerone said that the level of hatchery production in Alaska—as much as 1.8 billion juveniles per year—far exceeds the numbers of hatchery fish produced in the Columbia River.
Salmon productivity is also influenced by ocean conditions. Warming effects of climate change have hurt salmon runs that originate farther south, but has substantially increased productivity in runs from farther north. "There are winners and losers, and with the warming climate we're seeing, the winners are up north," Ruggerone said.
The study found that a warming ocean and abundant salmon competitors combined to reduce survival for southern stocks of sockeye, including those from the Fraser River in British Columbia, where at-risk sockeye runs were further hampered by a landslide that blocked passage to spawning grounds.
But for northern stocks, a warmer ocean is increasing sockeye survival, which appears to partially offset the negative effects of competing with pink salmon. While competition with pink salmon did reduce sockeye survival in the northern end of their range, sockeye were still able to increase survival rates by about 5 percent from 2005 to 2015 because of the positive effects of a warmer ocean.
However, without the negative effects of 82 million hatchery pink salmon, sockeye survival would have increased by approximately 10 percent, the study found.