California Sea Lions Are Dying—Now Scientists Know Why

Several sea lions have been found dead and dying along the California coast, with scientists suspecting a bacterial disease is the culprit.

Twelve dead sea lions were found in Bodega Bay, with 10 more in the city of Fort Bragg. Over 70 sick sea lions were taken to the local Marine Mammal Center. Samples from the sick and dead sea lions revealed that the mammals were suffering from an infection of leptospirosis.

Bodega Bay resident Megan Robbins told local newspaper The Press Democrat that the beach would usually get only three dead sea lions every year, but this week alone she saw five. "It's crazy," she said. "I've never seen anything like this."

Leptospirosis, a disease caused by leptospira bacteria and spread via urine and other body fluids, can lead to kidney damage, according to the U.S. Centers for Disease Control and Prevention.

The sick sea lions taken in by the Marine Mammal Center were underweight and had stomach ulcers. They behaved lethargically, and many had their flippers tucked into their bodies.

"It's because they are in a lot of pain," said Giancarlo Rulli, a Marine Mammal Center spokesperson, according to San Francisco news site SFGate. "When they're coming ashore like this, it's a bad sign."

"Leptospirosis is a bacterial disease that attacks the kidneys and leads to loss of function and ultimately death," Elliott Hazen, an ecologist at the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center, previously told Newsweek. "Leptospirosis definitely can lead to mortality due to kidney failure."

The disease can spread among animals in close contact with one another, such as at sea lion haul-outs, where they gather to mate, give birth and rest.

"These sea lions do forage collaboratively at sea but come back to land regularly, particularly juveniles and females," Hazen said. "Whether at colonies or at resting beaches, they overlap in high density and thus can lead to a higher chance of disease spread."

Many of the dead sea lions were too badly decomposed to test for leptospirosis, but the number of sick ones with the disease indicated that the dead ones likely died from the condition.

"What we're seeing is carcasses washing up on beaches that are adjacent to normal sea lion haul-outs," Sue Pemberton, a curatorial assistant for the California Academy of Sciences, told SFGate. "They would be living on rock soft shore, and then when they die there, a high tide washes them out."

Leptospirosis can also infect humans if they come into contact with an infected animal's body fluids, but this is very uncommon.

"Theoretically, yes, it could spread to humans, as they will shed spirochetes in urine," Chris McKnight, a biologist at the University of St. Andrews' Sea Mammal Research Unit, previously told Newsweek. "But the likelihood of a human coming into contact with this is slim to none in comparison with the urine of a plethora of other terrestrial mammals in North America, as almost all animals are susceptible to lepto."

He went on: "It has flipped from sea lions to humans three times, I believe, before, all of which were researchers working on the sea lions and all of which developed renal failure, if my memory serves me correctly. But, as I say, the chances of this being any direct issue to humans in the area [are] slim to none whatsoever."

Dogs may be at more risk of catching the disease if they approach a sick or dead sea lion or go into an area where the sea lions may have urinated.

"The really important thing we stress is making sure that your dog is on a leash and both you and your pet are keeping a safe distance of at least 50 yards," Rulli said. A vaccination against the disease is available for dogs.

This current leptospirosis outbreak may last a few months, according to Pemberton, similar to the length of previous outbreaks. The most recent outbreak occurred in 2018, when 300 sea lions were tended to by the Marine Mammal Center.

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