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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.

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.”