Neurotoxin Taking a Toll on Sea Lions

Bailey, a dark brown sea lion, lay listlessly on the ramp in his pen last week here at the Marine Mammal Center in the Marin Headlands.

He had come to the hospital and rehabilitation center five days earlier from Moss Beach in San Mateo County, sickened by an illness that has become all too common in recent years.

The 300-pound, 4-year-old male is among a large number of sea lions that have stranded themselves after suffering from domoic acid poisoning. They have become sick after eating tainted sardines or anchovies.

The fish in turn had eaten tiny zooplankton that had ingested phytoplankton, algae that produced the domoic acid, a neurotoxin.

The sea lions “get disoriented and they have seizures,” said Denise Greig, a marine biologist at the center. “Then they’re really out of it -- they’re flat out on the beach.”

The Marine Mammal Center has seen twice the normal number of sick sea lions and other animals this year, 780 compared with about 400 last year at this time, said Kathy Zagzebski, manager of the stranding program.

Besides the domoic acid poisoning, a second environmental condition is exacerbating the problems: Mild El Nino weather has warmed the ocean, and the fish that the sea lions normally feed on are not in the usual places. The poisoned mother sea lions can’t help their pups, so the pups go out on their own before they are fully weaned. But they don’t know where to forage. “We’re seeing lots of skinny little sea lions,” Zagzebski said.

The young ones come to the center malnourished, dehydrated and with parasites, she added. The center’s workers rehydrate them, restore their electrolyte balance with tube feedings and give them medicine to deal with the parasites. Within a few days, they are able to resume feeding on their own.

During a visit to the Marine Mammal Center last week, 28 California sea lions were recuperating in the sun in their outdoor pens. Skinny yearlings with their ribs showing were huddled next to the bigger ones. Few splashed around in their tanks.

A tan adult female sea lion who arrived last month from Oceano Dunes in San Luis Obispo County was slightly weaving, bobbing her head, a sign that she was still recovering from food poisoning.

Another, who had arrived two days earlier from San Luis Obispo, was motionless.

“Puddles is not doing well today,” Greig said. “She’s had a lot of drugs to prevent her from seizing.”

The center’s veterinarians were taking a blood sample to see if she should be treated for anything else, Greig said.

Sea lions were recovering from other injuries as well. One was healing from a gunshot wound between his eyes, while another was recuperating from a shark bite.

But the number of sick animals has declined compared to the onslaught of animals that came in earlier this year; more than 100 were treated at the center in May and June.

Major algae blooms have resulted in domoic acid poisoning this year in Southern California as well, where other rescue groups treat sick animals.

The Marine Mammal Center has 800 volunteers who respond to calls of sick or injured sea lions, seals, otters, porpoises and other marine mammals along 600 miles of coast from Mendocino to San Luis Obispo, said Jennifer Witherspoon, center spokeswoman.

The volunteers spring into action after the center gets calls of beached animals from the public, rangers or law-enforcement officers.

It is against federal law to harass, injure, feed or even approach the animals closer than 50 feet.

To see how the sea lions are faring after they’ve recovered, three of them so far have been outfitted with satellite global positioning tags that track their movements. Before being released, they got magnetic resonance imaging to see if the seizures had caused brain damage.

Two sea lions, Killer, who was released into San Francisco Bay, and Neptune, who was released at Moss Landing, are being monitored. Data are being collected on how deep they’re diving, how long it takes them to dive, the temperature of the ocean, and whether they’ve hauled out on land.

Kate Thomas, a graduate student at the Moss Landing Marine Lab who is monitoring the sea lions, said they seem to be doing well.

A third sea lion, which was released May 15, eventually was euthanized after it kept beaching itself and suffering seizures.

Zagzebski said domoic acid poisoning was first identified in sea mammals in 1998. At that time, the center was able to save about one-third of the animals that contracted the illness. In 2000, after another outbreak, the survival rate went up to 50%. And this year, one-half to two-thirds of the sick animals are expected to recover.

Zagzebski said experts believe there also was an outbreak of the poisoning in 1992-93, but they didn’t have the technology to identify it.

“The events may be happening more, or we’re more tuned in to it,” she said.

To better understand the phenomenon, oceanographers, algae researchers, county health officials and scientists are studying the algae blooms.

“The suspicion is that the increase and frequency [of harmful algae blooms] may be due to human impacts,” Zagzebski said.

Researchers believe treated sewage and agricultural runoff ending up in the ocean may be providing more nutrients for the algae, resulting in the blooms, she said.