Climate change in the last century is apparently linked with the extraordinary growth of many wild Pacific salmon populations in the subarctic North Pacific Ocean and the Bering Sea. Now scientists find the fact that pink salmon became so numerous has in turn exerted pervasive effects on ocean ecosystems. The findings are detailed in the Proceedings of the National Academy of Sciences.
Since the mid-1970s, the numbers of wild salmon in the subarctic North Pacific Ocean and the Bering Sea have grown greatly, particularly of pink salmon. The general explanation for this rise is climate change, with salmon numbers linked to shifts in the strength and position of the Aleutian Low, one of the main centers of activity in the atmospheric circulation of the Northern Hemisphere. These changes altered winds and ocean temperatures in ways that improved living conditions for pink salmon and influenced the plankton, squid and fish that salmon depend on for their survival.
These past findings supported the prevailing view that most biological change in ocean ecosystems, apart from human effects, is driven from the bottom up. Now researchers suggest that pink salmon have become so numerous that they are having a top-down influence on ocean ecosystems.
“Pink salmon are having a destabilizing effect on the open ocean ecosystems of the subarctic North Pacific and Bering Sea,” says researcher Alan Springer, a marine ecologist at the University of Alaska, Fairbanks.
Pink salmon are the most abundant of the wild Pacific salmon. Springer and his colleague Gus van Vliet noted the growth in pink salmon populations was adversely influencing their competitors. For instance, past research showed that the short-tailed shearwater, a seabird that spends the winter in the subarctic North Pacific Ocean and the Bering Sea, had lower body masses and liver masses and greater numbers of them died when pink salmon numbers were up.
The researchers analyzed seasonal patterns of 16 seabird species, including both omnivores and planktivores in the southern Bering Sea and Aleutian Islands. They found strong evidence that pink salmon had a major influence on the diets, clutch size, hatching success and other aspects of life of one or more of those seabird species at one or more of those islands.
“We know so little about how those ecosystems work, but are now gaining more insight into the magnitude of the effect of pink salmon, and all the salmon in aggregate, on the ecosystem as a whole and on individual species that we know are important components,” Springer says.
These findings suggest national and international conservation policies need to consider the effects that pink salmon can have on marine ecosystems. They hint that larger harvests of pink salmon and reduced hatchery production of pink and chum salmon might be encouraged.
“Salmon ranching in the open ocean is one important solution for world hunger and the need for protein,” Springer says. “But is it sustainable?”
Springer notes that future research should attempt to find similar evidence of the effects of salmon in these and other ecosystems.