Sea otters’ illness may stem from neurotoxin
Symptoms point to blight that crippled crab industry
Two California sea otters are being treated at a Bay Area rescue center for brain lesions apparently caused by the same neurotoxin that closed down the Dungeness crab fishery two years ago and killed hundreds of other sea creatures, officials said.
Veterinarians at the Marine Mammal Center in the Marin Headlands are rehabilitating the animals and fitting them with high-tech transmitters that they hope will help solve the mystery of why the shellfish-loving mammals have not recovered from the ravages of the longbanned fur trade, which left them on the brink of extinction.
Center officials said Otto, an 8-year-old otter found on a beach in San Luis Obispo County, and Yankee Doodle, an adult male rescued near Pillar Point Harbor north of Half Moon Bay, are both showing signs of neurologic disease caused by exposure to domoic acid, a toxin produced by algae blooms in the ocean.
Shawn Johnson, the director of veterinary science, said the center cannot determine exactly when or how the otters were poisoned because toxins can build up slowly in their system.
“They could have been contaminated weeks or even months prior,” Johnson said. “There are domoic acid blooms all up and down the coast throughout the spring and summer.”
Since June, the veterinary teaching hospital has treated 89 animals, all but seven of them sea lions, for exposure to domoic acid, which accumulates in crabs, mussels, clams and other shellfish.
Most of the sea lions were plucked off beaches near San Luis Obispo, where a large algal bloom has formed in the ocean. Otto was found in May stranded on a beach in Morro Bay, very close to the outbreak. Yankee Doodle was found July 3 in Half Moon Bay, many miles away.
It’s not clear whether the Bay Area poisoning case means a new algae bloom is cropping up or that toxins from an old one are still infecting marine life, Johnson said.
The two otters “are from completely different parts of the coast,” Johnson said, “so they were probably exposed in a very localized area near where they were stranded.”
This is the first year since 2003, when the Marin Mammal Center opened a new facility in the hills above Rodeo Beach, that veterinarians have treated sea otters, which are smart, destructive and escapeprone. Workers retrofitted two existing pens to keep the otters from climbing up the fencing, opening gates or using their paws to snatch and stash items left lying around by veterinary staff.
Some 20,000 California sea otters once lived along the coast of California and Baja, including a big population in San Francisco Bay, but fur traders seeking their luscious coats nearly wiped them out. The animals, also known as southern sea otters, haven’t been spotted in the bay since the early 1800s, and there have been fewer than 20 confirmed sightings in the Bay Area since 1979, according to the U.S. Fish and Wildlife Service.
The population of the frolicsome mammals, which now range from Half Moon Bay to Point Conception in Santa Barbara County, has held steady at only a few thousand for more than a decade despite intensive efforts to increase the population. They have been listed as threatened under the federal Endangered Species Act for 40 years.
Marine biologists believe great white shark attacks are at least partially to blame for hampering the ability of sea otters to repopulate their historic range, but domoic acid poisoning could also be playing a role.
Domoic acid attacks the brain and can cause confusion, seizures and death in sea lions. An MRI of Otto’s brain revealed a shrunken hippocampus, the area of the brain known to play a role in memory and navigation. Lesions were also found in the brain of Yankee Doodle.
Radio transmitters and new satellite-linked tools called Life History Transmitters were surgically implanted Thursday in the abdomens of the two otters, which the center hopes to release sometime this month.
The transmitters, which track locations, water depths and movements, are designed to send out data only when exposed to the air, which means scientists get an information dump after the animals die and decompose or are ripped apart by a shark. Johnson hopes the transmissions will shed light on the elusive species.
Johnson’s crew plans to monitor the animals before their release to determine whether they suffered permanent brain damage.
“We are basically starting from scratch to determine how domoic acid affects sea otters,” Johnson said. “We hope to better understand why sea otters aren’t moving north or south out of their traditional range.”
The center has admitted one other otter this year, a young female called Hope, who was stranded in April near San Simeon in San Luis Obispo County. After a week, Hope died, and a necropsy found she had an advanced case of valley fever, a fungal disease unrelated to domoic acid.
Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@ sfchronicle.com Twitter: @pfimrite