It’s hard to deny that the antics of a California sea lion that showed up recently on San Juan Island are – let’s say – amusing.

In less than 24 hours, it gave chase to several boats, hoisted itself out of the water and onto the back of one, and then dueled with a dog and a mother and son during its temporary take-over of Jackson’s Beach.

But local biologists say there’s nothing funny about the affliction that the animal is probably suffering from. If they’re on target, its days could be numbered.

According to Dr. Joe Gaydos of SeaDoc Society, exposure to a naturally-occurring toxin known as domoic acid, produced by a common open-ocean algae, is likely the culprit behind the animal’s unusual exploits. He said the toxin, which affects the brain and is frequently deadly, would account for both its erratic behavior and the unusually great distance the adult female traveled from home.

It’s rare, Gaydos said, for a California female to venture into Washington’s coastal waters and rarer still to have one journey through the Strait of Juan de Fuca and into Puget Sound.

Amy Traxler of the Friday Harbor Whale Museum, coordinator of the local Marine Mammal Stranding Network, which has monitored the sea lion’s activities, agrees. Unlike California males, known to migrate great distances, she said females generally don’t venture far from breeding grounds along the coast of California and Mexico.

“It’s not uncommon to see males around this area but females rarely migrate very far from their rookeries,” Traxler said. “Most of the time the toxin works its way into the brain and it could be what’s causing this erratic behavior.”

Much smaller than Stellar sea lions, the California kind typically range from southern Oregon to northern South America. As a population, California sea lions have as of late been holding their own thanks in part, Gaydos said, to federal protection and the Marine Mammal Protection Act.

The last time a California female turned up in the San Juans — about a year ago — it was found lumbering along a Shaw Island waterfront road, seemingly dazed and confused, and blinded by a bout of domoic acid. Gaydos said that not long after what appeared to be a full-recovery, it had regained its sight and its appetite, the animal died of a brain seizure.

Domoic acid, Gaydos said, affects brain tissues and can leave an animal susceptible to seizures. Unfortunately, he added, animals stricken by the toxin rarely recover.

“Her long-term prognosis is not good,” Gaydos said.

Weighing about 200 pounds, the female was first sighted May 15 by a pair of unsuspecting fisherman in San Juan Channel who were stunned as it twice tried to climb onto the open-end of their small dory. Traxler said they grew even more bewildered when it succeeded on its second attempt. It took about 10 minutes to push it off the boat.

“They said it wasn’t aggressive once it got in the boat,” she said. “It just seemed like it couldn’t understand why they were so taken aback and wanted it out of their boat.”

Traxler said after being booted off that boat it evidently set its sights on another and took off in pursuit when the skipper, with two daughters onboard, shifted into high-gear and raced out of the area. The following day, it waddled onto Jackson’s Beach where it confronted several beachcombers, including a woman, her son and the family dog, before public safety personnel and members of the stranding network arrived and cordoned off the area. By the following morning it was gone and last seen, according to Traxler, resting on a Henry Island beach the following Monday afternoon.

For information about the stranding network or what to do if you encounter a marine mammal on the beach, visit www.whalemuseum.org, or call 378-4710; to report a marine mammal stranding call 1-800-562-8832. I