by PHUONG LE, Associated Press
In this undated photograph offered by the University of Washington, Southern resident killer whales swim off the coast of San Juan Island, Wash. (Jane Cogan/University of Washington through AP)
SEATTLE (AP) – Harbor seals, sea lions and a few fish-eating killer whales have been rebounding alongside the Northeast Pacific Ocean in latest many years. But that growth has include a trade-off: They’re devouring extra of the salmon prized by a singular however fragile inhabitants of endangered orcas.
Competition with different marine mammals for a similar meals could also be an even bigger drawback than fishing, no less than lately, for southern resident killer whales that spend time in Washington state’s Puget Sound, a brand new examine suggests.
Researchers used fashions to estimate that from 1975 to 2015, marine mammals alongside the U.S. West Coast ate dramatically extra chinook salmon – from 6,100 metric tons to 15,200 metric tons, in response to a examine revealed Monday within the journal Scientific Reports.
In the identical interval, salmon caught by industrial and leisure fishing from Northern California to Alaska declined from 16,400 to 9,600 metric tons.
“This really quantifies yet another pressure on recovering the salmon population,” stated co-author Isaac Kaplan, a badysis fishery biologist with the Northwest Fisheries Science Center, a part of NOAA Fisheries. Other threats to salmon embody habitat injury, dams and air pollution.
The emphasis usually has been on managing how fishing impacts salmon. But this examine brings the remainder of the ecosystem, together with predators, into the image, Kaplan stated.
Researchers have recognized marine mammals gorge on salmon in sure hotspots, together with the Columbia River between Oregon and Washington. But the predators could also be consuming much more within the ocean than thought.
The authors estimated how a lot salmon in several life phases 4 marine mammals ate based mostly on quite a few badumptions, together with their weight, food regimen and dimension. The species included California sea lions, Stellar sea lions, harbor seals and fish-eating killer whales.
The examine does an excellent job of accounting for who eats chinook salmon throughout its numerous life phases, stated Andrew Trites, professor and director of the marine mammal badysis unit on the University of British Columbia. He was not concerned within the examine. “They’ve identified some of the major players, but they haven’t identified them all,” akin to different fish, marine birds and porpoises, he stated.
The examine discovered killer whales, which elevated from 292 to 644, ate probably the most salmon when it comes to biombad, or weight, whereas harbor seals ate the best numbers of salmon, largely juvenile fish.
Scientists additionally discovered sure populations of fish-eating resident killer whales in southeast Alaska and Canada waters ate much more salmon. But the orcas that spend time in Puget Sound ate about the identical quantity they did 40 years in the past, largely as a result of their numbers have been comparatively fixed.
Puget Sound orcas, also referred to as southern resident killer whales, face better challenges than their orca counterparts farther north as a result of they’ve a narrower menu of fish shares and fewer accessible fish in contrast with what they want, Kaplan stated.
These whales have struggled because of lack of meals, air pollution and impacts from boats since they had been listed as endangered in Canada in 2003 and 2005 within the U.S. There are actually simply 76, down from a excessive of 140 many years in the past.
Marine mammal safety efforts together with the Marine Mammal Protection Act in 1972 have meant excellent news for different populations. Harbor seals, for instance, elevated 210,000 to 355,000.
Puget Sound orcas eat grownup chinook salmon – additionally referred to as king salmon as a result of they’re the biggest – that migrate again to Puget Sound waters.
“Every other one of those predators has a chance to eat that salmon before. They’re the last ones to sit at the table and get a chance to eat,” stated Brandon Chasco, lead creator of the examine and an Oregon State University postdoctoral pupil.
Meanwhile, harbor seals feast on hundreds of thousands of smaller, juvenile salmon as they migrate to the ocean from native rivers.
“They’re first in line to eat the prey before they become adults,” Chasco stated. “The question is whether those fish would have died in the ocean, or if they’re taking prey out of the mouths of predators farther downstream.”
The authors say efforts to revive threatened salmon runs could also be masked by the rising numbers eaten by these marine mammals.
The examine was paid for by the Pacific Salmon Commission, which was fashioned by the governments of Canada and the United States in 1985.