The California sea lion population has tripled over the last 40 years, according to a new study published in the Journal of Wildlife Management.
About 45 percent of the United States sea lion population is at San Miguel Island off the coast of southern California.
Resarchers looked at sea lion breeding grounds all over the coast, including islands near San Clemente, for the study.
In 1975, the California sea lion population was at 88,924. By 2014, it jumped to 257,606.
Some people have been bitten by sea lions along California's coast. There have been four sea lion attacks in the San Francisco Bay Area since December.
But why is the population booming?
Researchers say the increase came after a pesticide, called DDT, was outlawed. It became trapped in the blubber of female sea lions, causing reproductive failure. Once it was no longer used, more sea lion pups were born.
Another factor is fish conservation efforts, according to the study. More food for the sea lions means they are more likely to thrive.
Experts said an increase in the population could mean that there are more sea lions capable of attacking humans who get too close.
"There are a lot of people on our San Diego County beaches so seals and sea lion populations do start to get comfortable with people on the beaches," said Jody Westberg of the SeaWorld Rescue Team.
Crews at SeaWorld said they have seen an increase in sea lion pups that they have had to rescue and rehabilitate lately. They rescued a pup on Monday they said was lethargic and dehydrated.
"We're still trying to figure out what happened to him," said Westberg. "He could've gotten rolled around in these heavy waves and the high surf. These California seals and sea lions just want to come up and take a break and lie on our beaches."
But they add just because you are seeing more sea lions does not mean it is okay to touch them.
"When you're approaching these animals they don't always know what your intentions are," said Westberg. "The best thing to do is enjoy them from a safe distance."
SeaWorld experts add if you see an injured marine mammal, don't touch it. Instead, call their hotline at 1-800-541- SEAL (7325).