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Photo: Nicole Boliaux, The Chronicle
California’s sea lion population has rebounded after a series of catastrophes, according to a new report by the National Oceanic and Atmospheric Administration.
California’s sea lion population has rebounded after a series of catastrophes, according to a new report by the National Oceanic and Atmospheric Administration.
Photo: Nicole Boliaux, The Chronicle
Tourists take photographs of Sea Lions as they sunbathe on a dock at Pier 39.
Tourists take photographs of Sea Lions as they sunbathe on a dock at Pier 39.
Photo: Justin Sullivan, Getty Images
The Golden Bear from the Blue and Gold fleet passes the sea lions at pier 39.
The Golden Bear from the Blue and Gold fleet passes the sea lions at pier 39.
Photo: Lance Iversen, The Chronicle
Sea Lions sunbathe on a dock at Pier 39.
Sea Lions sunbathe on a dock at Pier 39.
Photo: Justin Sullivan, Getty Images
The sea lions at pier 39 which disappeared over Thanksgiving weekend are starting to trickle back.
The sea lions at pier 39 which disappeared over Thanksgiving weekend are starting to trickle back.
Photo: Lance Iversen, The Chronicle
A tourist takes a photograph of Sea Lions as they sunbathe on a dock at Pier 39 in San Francisco, California.
A tourist takes a photograph of Sea Lions as they sunbathe on a dock at Pier 39 in San Francisco, California.
Photo: Justin Sullivan, Getty Images
Sea Lions sunbathe on a dock at Pier 39 in San Francisco, California.
Sea Lions sunbathe on a dock at Pier 39 in San Francisco, California.
Photo: Justin Sullivan, Getty Images
The sea lions at pier 39 which disappeared over Thanksgiving weekend are starting to trickle back. Pier 39 estimated at their height as many as 1,700 took shelter on their floating docks, to date Thursday Feb. 25, 2010 maybe 80 have returned.
lessThe sea lions at pier 39 which disappeared over Thanksgiving weekend are starting to trickle back. Pier 39 estimated at their height as many as 1,700 took shelter on their floating docks, to date Thursday Feb.
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A northern fur seal pup nicknamed Pipester turned up at the front door of a Hayward ironworks shop on Jan. 20, 2016. The pup was taken in by the Marine Mammal Center for rehabilitation after they were notified by police about the animal.
lessA northern fur seal pup nicknamed Pipester turned up at the front door of a Hayward ironworks shop on Jan. 20, 2016. The pup was taken in by the Marine Mammal Center for rehabilitation after they were
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Pipester, left, on January 20, 2016 at the Marine Mammal Center in Sausalito, Calif. The center wanted to keep him there until he had enough blubber to be released back into the wild.
Pipester, left, on January 20, 2016 at the Marine Mammal Center in Sausalito, Calif. The center wanted to keep him there until he had enough blubber to be released back into the wild.
The wayward elephant seal hanging out near Highway 37 (tentatively named Tolay after the inlet she holed up in). The elephant seal was later tranquilized by animal experts and released at the Point Reyes National Seashore.
lessThe wayward elephant seal hanging out near Highway 37 (tentatively named Tolay after the inlet she holed up in). The elephant seal was later tranquilized by animal experts and released at the Point Reyes
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Chippy was a sea lion who made headlines in 2004 by swimming 60 miles up the San Joaquin River Channel to Los Banos and onto the back of a California Highway Patrol vehicle, giving him an obvious name.
Chippy was a sea lion who made headlines in 2004 by swimming 60 miles up the San Joaquin River Channel to Los Banos and onto the back of a California Highway Patrol vehicle, giving him an obvious name.
The 319-pound Chippy was taken to the Marine Mammal Center in Sausalito, where veterinarians found a bullet lodged in his head. Here he recovers next to a younger sea lion friend, Pi.
The 319-pound Chippy was taken to the Marine Mammal Center in Sausalito, where veterinarians found a bullet lodged in his head. Here he recovers next to a younger sea lion friend, Pi.
Photo: PAUL CHINN
Chippy made his way down Drake's Beach toward the ocean after being released at the Point Reyes National Seashore.
Chippy made his way down Drake's Beach toward the ocean after being released at the Point Reyes National Seashore.
Photo: ERIC RISBERG
Rubbish, a sea lion pup, stranded himself in the Marina District in 2015 — the second time he required rescue that year.
Rubbish, a sea lion pup, stranded himself in the Marina District in 2015 — the second time he required rescue that year.
Photo: Courtesy / The Marine Mammal Center
Our most famous marine visitor is Humphrey the humpback whale. He swam into the Bay in 1985 and up the freshwater Sacramento River into a narrow slough where he was in imminent danger before acoustic recordings of whale feeding grounds got him to turn around.
lessOur most famous marine visitor is Humphrey the humpback whale. He swam into the Bay in 1985 and up the freshwater Sacramento River into a narrow slough where he was in imminent danger before acoustic
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The Humphey saga, which lasted nearly a month before he swam out the Golden Gate, is commemorated in
Humphrey the Lost Whale: A True Story by Wendy Tokuda and Richard Hall with illustrator Hanako Wakiyama.
The Humphey saga, which lasted nearly a month before he swam out the Golden Gate, is commemorated in
Humphrey the Lost Whale: A True Story by Wendy Tokuda and Richard Hall with illustrator Hanako Wakiyama.
Humphrey, who returned to the Bay briefly in 1990, spawned many gifts, such as this pillow.
Humphrey, who returned to the Bay briefly in 1990, spawned many gifts, such as this pillow.
Delta and Dawn were mother and daughter humpback whales who swam 75 miles up the Sacramento River in May 2007. Veterinarians believed they had suffered infections from wounds incurred in vessel strikes.
Delta and Dawn were mother and daughter humpback whales who swam 75 miles up the Sacramento River in May 2007. Veterinarians believed they had suffered infections from wounds incurred in vessel strikes.
Photo: PAUL CHINN
The wounded whales rejected attempts to coax them back to salt water until a Marine Mammal Center rescue team used dart guns to inject them with antibiotics. They next day, they began making their way back to the ocean.
lessThe wounded whales rejected attempts to coax them back to salt water until a Marine Mammal Center rescue team used dart guns to inject them with antibiotics. They next day, they began making their way back to
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Crowds of spectators gathered along the Sacramento River to watch Delta and Dawn.
Crowds of spectators gathered along the Sacramento River to watch Delta and Dawn.
Photo: Kat Wade
Rescue boats followed the whales out as they passed under the Carquinez Bridge at a rate of 4 mph.
Rescue boats followed the whales out as they passed under the Carquinez Bridge at a rate of 4 mph.
Photo: Kat Wade, SFC
Fruitvale was a year-old sea lion found in Oakland on the median of Interstate 880 in June 2009 getting her name from the neighborhood near where she was found.
Fruitvale was a year-old sea lion found in Oakland on the median of Interstate 880 in June 2009 getting her name from the neighborhood near where she was found.
Photo: Marine Mammal Center
Fruitvale was treated for malnourishment at the Marine Mammal Center and released along with five other sea lions near the Farallon Islands, where fish abound.
Fruitvale was treated for malnourishment at the Marine Mammal Center and released along with five other sea lions near the Farallon Islands, where fish abound.
Photo: Russel A. Daniels, AP
Sea lions at Pier 39 in San Francisco.
Sea lions at Pier 39 in San Francisco.
Photo: Michael Macor, The Chronicle
Sea lions have rebounded, crowding docks near Pier 39 and attracting tourists. The approximately 250,000 of the pinnipeds along the California coast represent the optimum sustainable population, scientists say.
Sea lions have rebounded, crowding docks near Pier 39 and attracting tourists. The approximately 250,000 of the pinnipeds along the California coast represent the optimum sustainable population, scientists say.
Photo: Michael Macor, The Chronicle
People gather on Pier 39 to watch the sea lions, whose population has rebounded after a series of catastrophes, including a lack of food and algae poisonings.
People gather on Pier 39 to watch the sea lions, whose population has rebounded after a series of catastrophes, including a lack of food and algae poisonings.
Photo: Michael Macor, The Chronicle
The creatures crowd together on the docks. Scientists say that their number has reach the optimum level that can be supported along the West Coast.
The creatures crowd together on the docks. Scientists say that their number has reach the optimum level that can be supported along the West Coast.
Photo: Michael Macor, The Chronicle
Sea lions gather at Pier 39 on Wednesday, Jan. 17, 2018 in San Francisco , Calif.. The Sea lIon population has rebounded after a major die-off during the recent drought.
Sea lions gather at Pier 39 on Wednesday, Jan. 17, 2018 in San Francisco , Calif.. The Sea lIon population has rebounded after a major die-off during the recent drought.
Photo: Michael Macor, The Chronicle
Report: Sea Lion population bounces back to capacity levels
Fishermen and swimmers sure have seen a lot of sea lions — some of them snatching salmon off lines or nipping freestylers in the bay — but a study published Wednesday proves the blubbery pinnipeds are, in fact, all over the place.
The sea lion population has not only rebounded after a series of catastrophes — including a lack of food and algae poisonings — but the approximately 250,000 sea lions now living along the California coast also have reached what scientists say is the optimum sustainable population, according to the National Oceanic and Atmospheric Administration.
“That means we have done our job,” said Sharon Melin, a wildlife biologist for the agency’s Alaska Fisheries Science Center Marine Mammal Laboratory. “Its a good, healthy, strong population.”
The analysis of 39 years of data, published Wednesday in the Journal of Wildlife Management, found that the number of sea lions along the coast right now is below the high point in 2008, when an estimated 281,450 sea lions were frolicking along the West Coast. The last comprehensive analysis of the sea lion population in the study was in 2014, when 257,000 animals were counted. Melin said three years of unusually warm ocean temperatures have further reduced the population, but the current count is still within the optimal range set by the Marin Mammal Protection Act of 1972.
The numbers show a dramatic rebound from the days when rampant hunting and commercial exploitation of sea lions reduced their numbers to record lows. There were only about 90,000 of the pinnipeds along the West Coast in the 1970s, when Congress passed the law protecting the species.
But a healthy population of one species isn’t always good for other species, said Chris Yates, the oceanic agency’s assistant regional administrator for fisheries resources. It means there are more animals stealing catches off fishing lines, munching on endangered salmon and depleting the marine food supply for other predators, like southern resident killer whales in the state of Washington.
At least one sea lion has even taken to biting swimmers at San Francisco’s Aquatic Park, creating a fury among the many hardy souls who like to take morning dips before work.
“There’s a lot of California sea lions. That’s a good thing, but it also comes with a lot of pretty significant challenges,” Yates said. “It certainly doesn’t come without controversy and differing opinions about whether having this many sea lions is a good thing.”
Yates said experts are working on ways to protect salmon and other species favored by the fishing fleet from the pinniped hordes, but nobody has yet proposed culling the herd. He added that sea lions will remain protected under the act and does not foresee any changes in the management strategy.
Since reaching its carrying capacity in 2008, the sea lion population has fluctuated, weathering periodic setbacks like 2013, when an unprecedented number of sea lion pups were stranded on the beaches along the Southern California coast. The death toll reportedly reached its peak in 2014 and 2015, as atmospheric conditions heated up coastal waters to unusual levels, creating havoc on the local ecosystem.
Roughly 10 times the average rate of sea lions — more than 2,500 — ended up stranded on California beaches in 2015, according to the report. But the population began to bounce back in 2016, scientists found, when 18,000 pups were born on San Miguel Island.
“If we had looked only at the last five years, we would have thought sea lions were in a tailspin,” Melin said, noting that the study changed that viewpoint. “Because we know the history of the population, we can put the recent decline in perspective.”
It is suspected that domoic acid poisoning was a major killer over the past few years. The poisons are produced by a microscopic, single-celled species known as pseudo-nitzschia that grows thicker and faster in warmer, nutrient-rich seawater. It accumulates in shellfish, mussels, anchovies, sardines and herring, the primary food of sea lions.
The Marine Mammal Center, in the Marin Headlands, says an average of about 70 poisoned marine mammals have been poisoned by domoic acid blooms each year since 2009. Although it is clearly a major biological threat, Melin said, recent outbreaks appear to have had “a fairly mild impact” on female sea lions and older juveniles and it is “unlikely to be the primary cause of a reduction in the population.”
Unusual wind, weather and atmospheric conditions that heated up coastal waters between 1 degree and 3 degrees and forced many species to migrate north certainly contributing to the decline, said Nate Mantua, a climatologist with the administration’s Southwest Fisheries Science Center.
“What we’ve been seeing is large year-to-year variation,” he said. “We think long term global warming is making these extremes more likely.”
Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com. Twitter: @pfimrite
