Report: Recovery of West Coast marine mammals boosts consumption of Chinook salmon


A younger resident killer whale chases a Chinook salmon within the Salish Sea close to San Juan Island, Washington, in September 2017. Image obtained underneath NMFS allow #19091. Photograph by John Durban (NOAA Fisheries/Southwest Fisheries Science Center), Holly Fearnbach (SR3: SeaLife Response, Rehabilitation and Research) and Lance Barrett-Lennard (Vancouver Aquarium’s Coastal Ocean Research Institute)

CORVALLIS, Ore. – Recovering populations of killer whales, sea lions and harbor seals on the West Coast have dramatically elevated their consumption of Chinook salmon within the final 40 years, which can now exceed the mixed harvest by business and leisure fisheries, a brand new research finds.

While the restoration of marine mammals represents a conservation success, it creates advanced trade-offs for managers additionally charged with defending the salmon they prey on, the research concludes. The U.S. Marine Mammal Protection Act of 1972 protects all marine mammals, together with whales and pinnipeds (seals and sea lions) throughout the waters of the United States, and the Endangered Species Act protects 9 West Coast populations of Chinook salmon.

The research was printed Monday within the journal Scientific Reports, Oregon State University stated. The findings resulted from a collaboration of federal, state and tribal scientists within the Pacific Northwest, together with Oregon State University and NOAA Fisheries. The badysis was designed partly to know the pressures on Chinook salmon consumed by southern resident killer whales, which in distinction to different killer whale populations are endangered and present few indicators of restoration.

Southern residents spend a lot of the yr within the inland waters of Washington and devour about the identical quantity of salmon in the present day as they did 40 years in the past, the research discovered. The research means that, not less than in recent times, competitors with different marine mammals could also be extra of an issue for southern residents than competitors with human fisheries.

“We have been successful at restoring and improving the population status of protected marine mammals,” stated Brandon Chasco, a doctoral candidate at Oregon State University and lead writer of the research. “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 used fashions to estimate marine mammal consumption of Chinook salmon primarily based on a number of badumptions about their food regimen and the dimensions and weight of salmon. The researchers estimate that from 1975 to 2015, the yearly biombad of Chinook salmon consumed by pinnipeds (sea lions and harbor seals) and killer whales elevated from 6,100 to 15,200 metric tons, and from 5 to 31.5 million particular person salmon.

Over the identical time span, they discovered that annual fisheries harvest decreased from 16,400 to 9,600 metric tons, and from three.6 million to 2.1 million people.

Overall, a number of rising populations of resident killer whales in Canada and southeast Alaska are estimated to devour the biggest biombad of Chinook salmon, however harbor seals devour the biggest variety of people, together with juvenile Chinook salmon, in response to the research.

Salmon are anadromous: They migrate from dwelling streams to the ocean as juveniles, and return a number of years later as adults to spawn. Many of the salmon from the West Coast migrate so far as Alaska, and are topic to predation throughout each their northward and southward migrations, making southern shares of Chinook salmon prone to a bigger gauntlet of predators.

Salmon restoration packages underway up and down the West Coast have boosted numbers of untamed salmon, the badysis discovered. However, elevated predation by recovering marine mammals could also be offsetting reductions in leisure and business harvests, and “masking the success of coast-wide recovery efforts,” the scientists wrote.

Isaac Kaplan, a badysis fishery biologist at NOAA Fisheries’ Northwest Fisheries Science Center and a coauthor on the research, stated the researchers quantified solely certainly one of many challenges to Chinook salmon restoration.

“The higher we perceive the totally different obstacles to salmon restoration, the higher we are able to account for them as we plan and perform restoration packages,” Kaplan stated. “Recovery efforts must account for all of these challenges, and we’re providing more details about one important part of that picture.”

The Columbia River has beforehand been recognized as an space with excessive marine mammal consumption of salmon, particularly by seals and sea lions within the estuary. The researchers discovered that in 2015 within the Columbia River, harbor seals on the river consumed 14 metric tons of Chinook salmon, in comparison with 219 and 227 metric tons consumed by California and Steller sea lions, respectively.

Considering the consumption of simply grownup Chinook salmon in 2015, the researchers estimated that harbor seals consumed 1,000 grownup Chinook salmon, whereas California sea lions consumed 46,000, and Steller sea lions consumed 47,000.

“Consumption in the ocean is also a significant source of mortality, but has been largely unmeasured until now,” stated Chasco, a National Marine Fisheries Service-Sea Grant Population Dynamics Fellow within the Department of Fisheries and Wildlife in OSU’s College of Agricultural Sciences. “Now managers have more information to work with in balancing these difficult trade-offs.”

Study collaborators included researchers at NOAA Fisheries’ Northwest Fisheries Science Center in Seattle, Smith-Root, a fisheries conservation know-how agency in Vancouver, Washington; Western Washington University; Makah Fisheries Management in Neah Bay, Washington; the Washington Department of Fish and Wildlife; and the North Gulf Oceanic Society in Homer, Alaska.

The Pacific Salmon Commission funded the research.

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