Skip to main content

Saving San Francisco’s Sea Lions

Saving San Francisco’s Sea Lions | San Francisco

It’s been a busy few years at the Marine Mammal Center. This hospital for wild seals and sea lions has seen a record number of patients as a result of several environmental threats. We made the rounds with a veterinarian.

Leading “fish school,” serving up fish smoothies, taking an X-ray of a fractured hind flipper. Welcome to a day in the life of the Marine Mammal Center in the San Francisco Bay Area.

While the sea lion patients appear to be friendly, social creatures, when visiting the Mammal Center, the first thing to learn is that these animals are not to be fraternized with.

“Our goal is to release them back into the wild so that they’re wild and part of the natural ecosystem,” Marine Mammal Center director of veterinary science Dr. Shawn Johnson said. “If we start interacting with them too much, then they’ll view people as a source of food or entertainment. Veterinarians that are coming here to train, they don’t understand why we can’t touch the animals. We can’t do any treatments without sedations or anesthesia—they’re wild here. We try to keep them wild and dangerous.”

The Mammal Center has been nursing sick and injured mammals back to health since 1975. To date, the Center has treated more than 21,000 marine mammals that have been rescued from a 600-mile stretch of Central and Northern California coastline. Aside from sea lions, the center treats elephant seals, whales, sea otters, harbor seals, fur seals, dolphins, harbor porpoises, and more.

California sea lions were hunted to near-extinction in the early 1900s, but since the enactment of the Marine Mammal Protection Act in 1972, there has been a population boom along the Pacific Coast.

But today sea lions are facing new threats from coastal climatological features that include El Niño and the “Blob”—a massive body of abnormally warm water in the northern Pacific Ocean.

Warmer ocean temperatures are contributing to the growth and spread of marine algae blooms from Mexico to Alaska, which produce the neurotoxin domoic acid. Sea lions become infected with domoic acid indirectly by feeding on contaminated fish like herring and anchovies that have consumed the toxin. Domoic acid-contaminated seafood has also posed a threat to human food sources, and algae outbreaks have put fisherman and commercial fisheries out of work up and down the Pacific coastline.

A California sea lion is handled for an examination after being admitted to the Marine Mammal Center in the San Francisco Bay Area. Bill Hunnewell, The Marine Mammal Center

Although domoic acid is secreted and cleared by sea lions within 48 hours, the toxin has typically done its damage by the time patients are admitted to the Marine Mammal Center. The toxin enters a sea lion’s bloodstream, brain, and heart, leading to seizures, neurological abnormalities, and often death. The seizures and lesions that the sea lions suffer as a result of domoic acid poisoning are similar to the effects of temporal lobe epilepsy in humans.

The warming trends of the Pacific Ocean may also be leading to an increased number of stranded, emaciated sea lion pups that the center is rescuing. In 2015 alone, the Mammal Center rescued more than 1,000 stranded pups.

Biologists have discovered that sea lion mothers are now spending more time hunting out at sea for herring, sardines, anchovies, and other fish that are swimming toward cooler temperatures, in deeper waters away from the shore. The pups, left alone for several days, are starving to death because their mothers are unable to produce enough milk to feed them.

The stranded sea lion pups that make it to the Mammal Center for treatment are immediately provided with nutrition and hydration. Some of the pups are so young and helpless that they actually qualify for enrollment in the center’s “Fish School” training sessions, in which the staff teaches the sea lions how to eat dead herring with as little human interaction as possible.

More than 1,200 volunteers work at the Mammal Center. Treating the sea lions can be a difficult task, as just taking a simple blood sample requires anesthesia.

Examining an adult sea lion that suffered a fractured flipper from an apparent shark bite, Johnson explained that part of any exam for sea lion adults is to test for cancer. According to Johnson, sea lions have the highest prevalence of cancer of any wild species in the world and more than one-quarter of all adult sea lions that the center admits are diagnosed with cancer.

This cancer was first diagnosed in the 1990s. The causes of the cancer include herpes infections, coupled with high levels of toxins that prevent sea lions from fighting the herpes virus. The herpes virus triggers an uncontrollable growth of cancer cells that spreads throughout the sea lion’s body and eventually kills the animal.

Johnson is concerned that the illnesses the Marine Mammal Center is treating could be indicative of a broader trend.

“If these trends continue, it won’t be much longer until the entire California sea lion population starts to decline,” Johnson said. “From no pups, to domoic acid, to one quarter of adults having cancer, if you add them all up, all of these impacts on the sea lions can have a dire effect on their declining population. We want to restore these animals to health and return them to the system, but it’s also important to us to use these animals to learn more about the ocean health and use that message to educate the public that comes here to go into the classrooms and teach the kids about how some of these activities that humans are having are having a negative impact on the oceans, which then affects the marine mammals that are living in it.”

California sea lions populations have rebounded astoundingly since being hunted to near-extinction in the early 1900s, but have been threatened in recent years due to cancer and climate-related diseases. / Bill Hunnewell, The Marine Mammal Center

— Sean Keenehan

Media Manager ID