West Coast California Sea Lion
Meets Marine Mammal Protection Act Goal
It's probably no surprise to those who are tracking sea lions feeding on salmon and steelhead at Bonneville Dam or Willamette Falls that the California sea lion population along the West Coast of the U.S. and British Columbia is healthy and robust.
This week, NOAA Fisheries agreed, declaring California sea lions that in 1975 totaled just 90,000 to have fully rebounded under the protection of the Marine Mammal Protection Act of 1972. Protected by the MMPA, the population grew until in 2008 NOAA scientists estimated it to be 281,450. That, they said, was the carrying capacity, or optimum sustainable population (OSP), for the sea mammal in the California current ecosystem at the time.
Numbers reached an estimated high of 306,220 in 2012 before declining below carrying capacity in the years since as ocean conditions warmed and food became scarce, reducing the number to about 250,000 in 2013 and 2014, according to the first comprehensive population assessment of the species published this week.
Such a long-term reconstruction of the sea lion population has never been done before, said Robert DeLong, leader of the Alaska Fisheries Science Center's California Current Ecosystems Program and co-author of new research that has estimated California sea lion population and determined the population to have rebounded.
The long-term collaborative study, "Population Growth and Status of California Sea Lions," was published online Jan. 17, 2018 in The Journal of Wildlife Management.
DeLong's co-authors are Jeffrey Laake and Sharon Melin (wildlife biologist) at NOAA's Alaska Fisheries Science Center in Seattle; and Mark Lowry (research fisheries biologist) and James Carretta, NOAA's Southwest Fisheries Science Center in La Jolla, Calif.
NOAA's declaration that California sea lions have fully rebounded does not mean a "delisting" as it would if the sea lion was listed as threatened or endangered under the federal Endangered Species Act.
"Although there is no provision in the Marine Mammal Protection Act (which protects sea lions) to delist a species, there is a provision that allows states to ask NOAA Fisheries to take over management of species that have reached carrying capacity (in the law it is called Optimum Sustainable Population or OSP) and potentially do more to control their numbers," wrote NOAA spokesperson Michael Milstein when announcing the report's findings.
Even with the higher numbers of sea lions, there has been no call from California's fishing industry to begin culling the animals, according to Chris Yates, NOAA Fisheries, assistant regional administrator for NOAA's West Coast Region Protected Resources Division.
Besides, "culling has not proved to be a viable wildlife management tool," he said at a NOAA news conference Wednesday, Jan. 17.
In addition, Yates said, no single state so far has applied to assume full management of California sea lions and "I do not anticipate any state doing that."
NOAA, however, has allowed deterrence activities led by states at Bonneville Dam, as well as limited culling, called lethal removal of California sea lions, and the agency is now considering a request from the Oregon Department of Fish and Wildlife to begin lethal removal of California sea lions at Willamette Falls.
The sea lion population is healthy and robust, the new research found, and its recovery over the past several decades reflects an important success for the MMPA, which recognized marine mammals as a central element of their ocean ecosystems, setting population goals based on levels that would contribute to the health and stability of those ecosystems, NOAA said in a news story at https://www.fisheries.noaa.gov/feature-story/california-sea-lion-population-rebounded-new-highs?utm_medium=email&utm_source=govdelivery.
"The population has basically come into balance with its environment," said co-author Melin, who has tracked sea lion numbers in Southern California's Channel Islands for years. "The marine environment is always changing, and their population is at a point where it responds very quickly to changes in the environment."
The goal now, she said during the news conference this week, is to keep the population balanced between 183,000 and 275,000 individuals.
Scientists combined the results of sea lion pup counts in the Channel Islands, aerial surveys of sea lion rookeries, survival rates and other information to reconstruct the growth of the sea lion population from 1975 to 2014. They gained enough insight into the dynamics of the population to fill in gaps from a few years with little data.
Market hunting, bounties, pollutants such as DDT and other forces depressed sea lion numbers in the middle of the last century.
Still, the researchers are finding sea lion numbers to be very sensitive to environmental changes, especially changes in ocean temperatures that affect their prey. Their models based on past population shifts predict that an increase of 1 degree C in sea surface temperature off the West Coast will reduce sea lion population growth to zero, while an increase of 2 degrees will lead to a 7 percent decline in the population.
"When the California Current is not productive, they respond pretty fast and dramatically," Melin said. "They're out there in the ocean sampling it all the time. That makes them a very powerful indicator of what's happening in the marine environment."
An unusual marine heat wave off the West Coast known as "the blob" combined with an El Niño climate pattern reduced pup production and survival and thousands of malnourished pups were stranded on Southern California beaches, NOAA said. It declared the elevated number of deaths an unusual mortality event in 2013. Subsequently, the sea lion population dropped to just over 250,000 in 2013 and 2014, the last years for which the agency has population estimates.
"This is not just a story about continued growth of the population," DeLong said. "These last several years have brought new environmental stresses to the California Current, and we've seen that reflected by the sea lions."
Understanding the relationship between sea lion numbers and the environment can help scientists detect signals of coming change, NOAA said. Wildlife managers can then use that information to anticipate and prepare for shifts in the ecosystem and its inhabitants.
"It helps us to understand the factors driving this population, because we can incorporate them into management decisions," Yates said.
The general recovery of sea lion numbers has had other consequences on the West Coast, including conflicts with people over beach access where sea lions haul out and concern about sea lion predation on threatened and endangered salmon and steelhead in the Columbia River basin.
NOAA Fisheries has authorized Oregon, Washington and Idaho to remove individually identifiable sea lions near the Columbia River's Bonneville Dam that have been spotted repeatedly preying on fish protected under the Endangered Species Act. The species still maintains OSP levels even when small numbers of adult males are being removed to protect salmon runs and climate events are depressing growth.
That suggests that the removal of a limited number of sea lions in such programs is unlikely to affect the population as a whole, Melin said.
She stressed the value of long-term data in understanding the dynamics of the population. "If we had looked only at the last five years, we would have thought sea lions were in a tailspin," she said. "Because we know the history of the population, we can put the recent decline in perspective."
The MMPA is a very restrictive statute and affords these animals a lot of protection," Yates concluded. "This study does not change that. California sea lions are still protected."
Recovery Of West Coast Marine Mammals Dramatically Increasing Consumption Of Chinook Salmon by Staff, Columbia Basin Bulletin 12/1/17
NOAA Invites Comments On Lethal Removal Of Sea Lions At Willamette Falls; Threat To Listed Steelhead by Staff, Columbia Basin Bulletin 12/1/17
Biologists Tell Council That Sea Lion Predation Puts Willamette Winter Steelhead At Extinction Risk by Staff, Columbia Basin Bulletin 9/22/17
ODFW Analysis: With Continued Sea Lion Predation Willamette Winter Steelhead At Risk Of Extinction by Staff, Columbia Basin Bulletin 8/11/17
Oregon To Seek Permit To Lethally Remove Salmonid-Eating Sea Lions At Willamette Falls by Staff, Columbia Basin Bulletin 6/23/17
NOAA Re-Authorizes States To Lethally Remove Salmon-Eating California Sea Lions At Bonneville Dam by Staff, Columbia Basin Bulletin 7/15/16
Final 2016 Pinniped Report: Sea Lion Salmon Take Astoria To Bonneville Dam Could Be 20 Percent Of Run by Staff, Columbia Basin Bulletin 6/17/16
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