Flurry of sick and dying sea lions around Bodega Bay believed to be caused by bacterial disease

An unusual flurry of sick and dead California sea lions coming ashore in and around Bodega Bay is believed to have been caused by a wave of bacterial disease among mostly immature males returning to the coast from breeding grounds in The Channel Islands, a spokesman for The Marine Mammal Center said Tuesday.

Bodega Bay, especially Doran and Salmon Creek beaches, are among several hotspots along the California coast where an unusually high number of sea lions have been found to be suffering from leptospirosis, said Giancarlo Rulli, marketing and communications associate for the Sausalito-based marine mammal hospital, the state’s largest. Other sites with high numbers of ailing sea lions include San Luis Obispo, Monterey and Mendocino-Fort Bragg.

The animals are mostly coming ashore in places where they normally haul out to rest, according to Sue Pemberton, a curatorial assistant in the Ornithology and Mammalogy Department at the California Academy of Sciences.

About 12 sea lion carcasses have been reported around Bodega Bay and another eight or 10 have been found in Fort Bragg, Pemberton said.

Others have been captured and taken to the Marine Mammal Center for treatment, usually involving supportive fluids and antibiotics, Rulli said. A handful were rescued around Bodega Bay, the majority of them confirmed to be infected with leptospirosis, he said.

Though post-mortem examinations called necropsies have not been performed on those found dead, results from those that have died while in treatment suggest an uptick in leptospirosis, as well, experts said.

It is unrelated to a surge in poisoning of marine mammals in Southern California earlier this summer from Domoic acid, a naturally occurring neurotoxin produced by certain algae. Sea lions were among the hundreds of animals affected in the recent southerly outbreak and have been sentinels of its appearance in northerly waters in the past, as well.

The more recent issue, leptospirosis, is a bacterial infection that can affect many different animals, including dogs, causes lethargy, mild to moderate weight loss and severe dehydration, attacking the kidneys and eventually causing failure. They also can suffer from stomach ulcers.

Sick sea lions are often seen with their flippers tucked close to their bodies, an indication of the discomfort caused by their failing kidneys, Rulli said.

“The impact of having kidney failure is they’re coming ashore because they’re in so much pain,” he said. “If they’re coming ashore, they’re in very bad shape.”

Historically, only about a third that are hospitalized will survive, he said.

Mostly 2 to 4 years old, they are still sexually immature but instinctively travel to breeding grounds off shore of Southern California to observe and learn how to fight for a mate, Rulli said.

Leptospirosis, concentrated in urine and other body fluids, is easily transmitted when the animals come together. The intensity varies year to year, and it is normal to see dead sea lions along the shoreline this time of year, but every four or five years or so, there is a large, cyclical outbreak, Rulli said.

More than 300 sea lions were hospitalized with the disease in 2018, a record year, for instance, Rulli said. This year, so far, it’s been around 70, though only about 20 are hospitalized currently because of fatalities and a few discharges, but it does not appear to be one of the larger outbreaks, he said. Experts are unsure what the impact of climate change may be on the regular cycle of the bacteria, however.

About five animals still in the wild are under observation by Marine Mammal Center volunteers to see if they need help, Rulli said.

Sea lions or other marine mammals that appear sick or in distress but are still alive should be reported to The Marine Mammal Center hotline at 415-289-SEAL, or 415-289-7325.

Dead animals should be reported to the California Academy of Sciences, at 415-379-5381.

Humans, especially those with dogs, should give sick or dead sea lions a wide berth, since many of their diseases, including leptospirosis, can be transmitted, Pemberton said.

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.