A record number of seals and sea lions for this time of year have been admitted to California treatment facilities. The lead vet working with the animals blames a "perfect storm" of causes, including a toxic algal bloom and seasonal factors.
The nonprofit Marine Mammal Center has taken in 386 animals since January 1, more than during any previous year up to this date, says Shawn Johnson, the group's top veterinarian. The center's headquarters is in Sausalito, though it maintains satellite offices in Mendocino, Monterey, and San Luis Obispo Counties.
The Marine Mammal Center typically treats 600 to 800 marine animals per year, a number that has been trending upward. In all, the center has rescued more than 18,000 animals since it was founded in 1975.
Animals rescued so far this year include 202 California sea lions, 145 elephant seals, 33 harbor seals, four Guadalupe fur seals, and one northern fur seal.
Hoppie's Incredible Journey
Hoppie was rescued by the Marine Mammal Center after he was found about 100 miles (160 kilometers) inland on March 31, in the San Luis National Wildlife Refuge in central California. Johnson says he suspects Hoppie swam up the San Joaquin River, became disoriented, and then left the water.
"It's really unusual for sea lions to go that far inland," says Johnson, who said he knows of only one other case of a sea lion straying so far from the ocean.
Sea lions often travel short distances up rivers, he says. But sometimes, "little pups get so lost they don't know where they are going, trying to figure out where some food is."
By the time a good Samaritan discovered Hoppie and called the center, the pup was underweight and malnourished. Since arriving at the center, however, he has been doing well, says spokesperson Laura Sherr.
"He has been eating well and swimming around the pool," and the staff is optimistic that he will be released before long, says Sherr.
Overall, roughly half of the animals the center takes in are successfully released back into the wild.
"Perfect Storm" of Problems
Johnson says the high number of rescued seals is due to a "perfect storm" of factors. First, the center has been treating many elephant seal pups that were weaned from their mothers too soon.
"The pups went to forage on their own, they didn't quite figure it out, and then they washed up on beaches, where they were thin," he says.
The same thing has been happening to California sea lion pups in high numbers, he adds.
Sherr says people find distressed animals on beaches and then call the center's 24-hour hotline. A network of 1,100 trained volunteers up and down the coast respond to calls. The volunteers assess the animal, and if it needs help, they transport it to one of the center's facilities.
Another problem this year is a large algal bloom in Monterey Bay. Scientists don't know what causes the bloom, but the tiny diatoms release a toxin called domoic acid. That compound is taken in by small fish and shellfish, which seem unaffected, says Johnson. But then larger fish consume the smaller animals, and the domoic acid is concentrated through a process known as bioaccumulation.
When seals eat the larger fish, they may consume high levels of domoic acid. That can cause memory loss and seizures. The chemical poses a similar risk to people, who are currently advised by officials to avoid certain types of seafood from Monterey Bay.
The Marine Mammal Center has treated around 40 sea lions, mostly adults, for domoic acid poisoning this year. There is no antidote to the toxin, so rescuers rely on supportive care, including administering fluids and antiseizure drugs.
If medication fails to stop seizures, which happens occasionally, the animal must be euthanized, says Johnson. Those that show evidence of significant neurologic damage also must be euthanized because they won't be able to function in the wild. In most cases, the animals do recover and are released.
Asked about the outlook for the rest of the year, Johnson says, "There are almost 300,000 sea lions in California, so it could get worse before it gets better. Hopefully the algal bloom will subside soon."
But he adds, "There's a worry that if we have a large El Niño this fall, it will have a detrimental effect on our animals."
Johnson says young sea lion pups usually learn how to fish by watching their peers. But some elephant seal pups aren't so lucky and must be taught.
Those pups are enrolled in the Marine Mammal Center's "fish school," in which they are introduced first to dead herring in a pool. The staff then present fish with tongs and pull them along with string. Finally, live fish are introduced.
"Once they grab a fish, it takes them a while to learn how to swallow," Johnson adds. Eventually, they get the hang of it.
Hoppie has been eating five pounds (2.3 kilograms) of herring a day. Overall, the center has been serving about a thousand pounds (454 kilograms) of Alaska herring a day, at a cost of about one dollar per pound. The funding comes mostly from individual donors.
"This year has been extraordinary for us," says Johnson. "We're hoping that these numbers will level off and go back to our normal pace for the rest of the year, but it's really hard to predict."