Marine mammals on the West Coast may now be eating more Chinook salmon than those being caught by commercial and recreational fisheries combined, a new study finds.
It shows that recovering populations of killer whales, sea lions, and harbor seals have dramatically increased their consumption of Chinook salmon in the last 40 years.
"We have been successful at restoring and improving the population status of protected marine mammals," said Brandon Chasco, a doctoral candidate at Oregon State University and lead author of the study. "But now we have the potential for protected seals and sea lions to be competing with protected killer whales, and all of which consume protected Chinook salmon."
The research was a collaboration of federal, state and tribal scientists in the Pacific Northwest, including Oregon State University and NOAA Fisheries.
It may have serious implications for the recovery of both Southern Resident killer whales as well as Chinook salmon, both of which are protected by the Endangered Species Act. There are only 76 Southern Resident killer whales alive today, deeply concerning for scientists who believe the orcas may disappear if serious action is not taken immediately.
Southern residents spend much of the year in Puget Sound and the Salish Sea, and their primary diet is Chinook. The study found that the orcas consume about the same volume of salmon today as they did 40 years ago. It suggests that in today's ecosystem, competition with other marine mammals may be more of a problem for southern residents than competition with human fisheries.
The study also shows that several growing populations of resident killer whales in Canada and Southeast Alaska are estimated to consume the largest biomass of Chinook salmon, but harbor seals consume the largest number of individuals, including juveniles which are a main target for habitation restoration efforts around Puget Sound and the Columbia River.
The research found that salmon recovery programs up and down the West Coast have boosted numbers of wild salmon, but increased predation by recovering marine mammals presents a challenge and may offset reductions in recreational and commercial harvests.
"The better we understand the different obstacles to salmon recovery, the better we can account for them as we plan and carry out recovery programs," said Isaac Kaplan, a research fishery biologist at NOAA Fisheries' Northwest Fisheries Science Center and a co-author on the study. "Recovery efforts must account for all of these challenges, and we're providing more details about one important part of that picture."
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