California Sea Lion Population Rebounded to New Highs

Sea lion numbers reflect conditions in California Current through the decades.

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. The landmark 1972 legislation 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.

The MMPA calls those levels the Optimum Sustainable Population (OSP), and provides options for states to take over management of species that have reached their OSP.

Adult male California sea lions are identified by their large size, dark brown fur and conspicuous crest on their forehead. Adult females are blonde to light brown and are smaller than the adult males. Pups are dark brown to black.

California sea lions have now reached those levels, according to the new assessment by scientists from NOAA Fisheries’ Alaska Fisheries Science Center and Southwest Fisheries Science Center. They published the results of the long-term collaborative study today in the Journal of Wildlife Management.

“The population has basically come into balance with its environment,” said coauthor Sharon Melin, a research biologist at the Alaska Fisheries Science Center 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.”

California sea lion frolicking near the rookery at San Miguel Island, California.

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.

Video: California Sea Lion Rookery on San Miguel Island

Market hunting, bounties, pollutants such as DDT and other forces depressed sea lion numbers in the middle of the last century. The new study found that the species then rose from less than 90,000 animals in 1975 to an estimated 281,450 in 2008, which was roughly the carrying capacity for sea lions in the California Current Ecosystem at that time. It then fluctuated around that level, reaching a high of 306,220 in 2012 before declining below the carrying capacity in the years since as ocean conditions changed.

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 a coauthor of the new research.

The researchers found sea lion numbers 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.”

A quarter million?! California sea lion population has tripled, new study finds

Sea lions bask in the winter sun Monday afternoon, Dec. 14, 2015, at Pier 39 in San Francisco, Calif. A research study published in this week’s issue of the journal Science reports an increase in the number of the mammals sickened by domoic acid, a toxin produced by naturally occurring marine algae. (Karl Mondon/Bay Area News Group)

The West Coast’s population of California sea lions — the playful marine animals that delight tourists on the Santa Cruz waterfront and San Francisco’s Fisherman’s Wharf while competing with salmon fishermen for valuable catches — has tripled in the past 40 years to more than 250,000.

In a study released Wednesday, federal biologists say strict environmental laws to protect marine mammals have worked so well that California sea lions have become the first marine mammal that lives along the entire West Coast to recover to its natural carrying capacity. That’s the maximum population size a species can reach based on an area’s available food.

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“There have been ups and downs, but generally the trend has been upward,” said Sharon Melin, a biologist with the National Oceanic and Atmospheric Administration in Seattle.

In 1972, with the public alarmed that the hunting of whales and other animals was threatening to drive some species to extinction, President Richard Nixon signed the Marine Mammal Protection Act. One of the landmark environmental laws of the 20th century, the law cleared Congress on an overwhelmingly bipartisan vote that would likely be impossible today. The U.S. Senate passed it 88-2 and the House of Representatives 362-10. The law brought sweeping changes, making it illegal to hunt, kill, injure or harass any marine mammal, including whales, seals, dolphins and sea otters.

No longer hunted for their dense fur, sea otters have risen in number, and California gray whales — which were being killed from a whaling station in Richmond for Kal-Kan dog food as recently as 1972 — have bounced back so much that they have been removed from the federal Endangered Species list.

But California sea lions — which range from Mexico to Alaska — have exploded the most in number, jumping from an estimated 88,924 in 1975 to 257,606 in 2014, according to the new NOAA study.

But all the sea lions have caused problems.

They have broken docks and sunk boats at marinas. They have vexed salmon fishermen, following their boats and eating valuable fish off their lines.

“With some fishing days seeing as few as five to 10 fish, a commercial fisherman can still make money with 10 fish if they are $10 per pound, but if you’re losing them to sea lions that can have a major effect,” said John McManus, executive director of the Golden Gate Salmon Association in San Francisco.

The water boils with activity as sea lions, birds, dolphins and humpback whales feed on schools of anchovies less than a mile outside of the Moss Landing, Calif., in the Monterey Bay on Aug. 10, 2014. (Laura A. Oda/Bay Area News Group)

In December, three swimmers at Aquatic Park Cove in San Francisco suffered sea lion bites, causing puncture wounds on their legs and arms that sent them to the hospital. The National Park Service closed the cove for a week, then reopened it Dec. 20, only to have another swimmer bitten last week. The area, popular with distance swimmers in San Francisco Bay, is now open, but posted with warning signs.

“Biting is an unusual activity,” said Lynn Cullivan, a spokesman for the National Park Service. “Swimmers are still seeing animals out there, but they aren’t being aggressive. We are telling people to stay toward the shore and swim with a buddy.”

Sea lions were once shot in large numbers. From 1900 until the early 1930s, Oregon paid a bounty of up to $10 per dead sea lion to make it harder for them to compete with commercial fishermen. Washington state paid $5 per dead sea lion in the 1950s, causing thousands to be killed. Until the Marine Mammal Protection Act in 1972, fishermen regularly shot them off the California coast.

NOAA’s Melin noted that federal lawmakers have amended the act to allow the killing of a few California sea lions that have eaten large numbers of endangered salmon. In 2008, federal officials gave a permit to Washington, Oregon and Idaho to kill about 80 sea lions a year that were congregating at the Bonneville Dam on the Columbia River, eating large numbers of endangered spring run chinook salmon. The permit, which caused an outcry among animal welfare groups, calls for sea lions that are repeat offenders to be branded with a mark. Then, if they continue to eat the fish, they’re trapped and euthanized.

“It is kind of a garbage-can bear situation where animals learn the behavior,” Melin said. “If you can keep animals from learning it, then they don’t go in there. It’s not a population level problem; it’s an individual problem.”

The reason that California sea lions have rebounded faster than other West Coast species is that they have a wide variety of prey they eat, including squid, herring, sardines, mackerel and salmon, she said.

But the sea lions are vulnerable to changing water temperatures. During recent El Niño winters, when warm water caused some fish species to move hundreds of miles from their normal habitats, California sea lion populations dipped, and coastal residents reported malnourished pups along the shoreline.

The population peaked in 2012 at 306,000. If climate change causes the ocean to warm another 1.8 degrees Fahrenheit, that could cause their population growth to stop. And if the temperatures rise at twice that amount, the population would fall by up to 7 percent a year, the NOAA study found.

For now, experts say, the sea lion rebound is a good sign that the Pacific Ocean is fairly healthy.

“This is the day that people who wrote these laws really envisioned,” said Jerry Moxley, a research scientist with the Monterey Bay Aquarium. “It’s a grand success. It’s something we can all celebrate as part of our shared heritage.”

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