Photo: Nicole Boliaux, The Chronicle
Scores of convulsing sea lions are washing up on Central California beaches after eating fish poisoned by a plume of toxic algae that could spread north toward the Bay Area and cause widespread problems, marine biologists said.
Since June, veterinarians at the Marine Mammal Center in the Marin Headlands have treated 89 animals — all but seven of them sea lions — plucked mostly off beaches near San Luis Obispo, where a large algal bloom formed in the ocean.
Of the 82 sea lions brought to the center, 31 have died, and virtually all of them had seizures caused by domoic acid, the dreaded neurotoxin that closed down the Dungeness crab season two years ago and killed off thousands of marine species over the past two decades, said Shawn Johnson, the center’s director of veterinary science.
“We’ve rescued 64 animals just in July,” said Johnson, who coordinates the rehabilitation of injured marine mammals rescued from San Luis Obispo to the Oregon border. “They’ve been coming in huge waves, as many as 10 a day.”
The coming crab season, which typically kicks off in November, is not currently being threatened, but state health officials are monitoring the situation to see if algal blooms begin cropping up farther north as ocean temperatures climb in the late summer and fall.
The stakes are high for the environment and for the fishing industry. More than 21 million pounds of Dungeness worth $66.7 million were pulled in during the 2016-17 season, the best haul in four years and almost double what was taken a year earlier when much of the California coast was blanketed in algae, prompting fishing restrictions and health warnings.
The latest bloom, known as a red tide, appears to be on a northward trajectory. Starting in April, dozens of sick and dying sea lions, dolphins and fur seals were found on beaches in the Los Angeles and San Diego areas.
Over the past two months, most of the poisoned sea lions, fur seals and sea otters have been washing up on beaches around Oceano Dunes State Vehicular Recreation Area in San Luis Obispo County, Johnson said. Many of the rescued sea lions were lactating females that had been foraging near the Channel Islands for food to feed their pups.
“To have them so concentrated in such a short time period is unusual. That tells us there is a really toxic bloom of algae in that area,” Johnson said. “As the water temperatures increase over the summer, we see this bloom migrating farther north, so it’s possible we could see it reach the Monterey Bay area in the late summer and fall.”
Outbreaks like this one have been sickening increasing numbers of marine mammals since the first toxic bloom was documented on the West Coast in 1998, when 400 sea lions washed ashore in Monterey Bay.
The culprit was a microscopic, single-celled species known as pseudo-nitzschia, which produces domoic acid. The algae grows thicker and faster in warmer, nutrient rich seawater, and the toxin it produces accumulates in shellfish, mussels, anchovies, sardines and herring, the primary food of sea lions.
When it is sufficiently dense, it attacks the hippocampus, the brain’s memory center, and can cause memory loss, tremors, convulsions and death. The toxin, which accumulates in the bloodstream, can also sicken people who eat fish, crab or mollusks.
Courtesy of sfchronicle.com