Thousands Of Leopard Sharks Wash Up Dead With Brains Eaten In California

Over the past few months, as many as 2,000 leopard sharks have died in the San Francisco Bay area. The California Department of Fish and Wildlife (CDFW) has not made determining the cause of death a priority due to limited resources.

According to Dr. Mark Okihiro, a research scientist with the CDFW, his department theorized a pathogen or parasite is the most likely cause of death. He said this pathogen or parasite became a larger threat in recent months because it targets a variety of species, explaining that a myriad of different fish were found dead in the San Francisco Bay.

“We’re pretty confident at this point. It’s called Miamiensis avidus,” he said to NBC Bay Area-affiliate KNTV. “It’s a small single-celled organism. It’s very similar to the common amoeba.”

The parasite swims up a shark’s nostril into its brain and eats away at it. The parasite incapacitates the shark, leaving it swimming aimlessly or causing it to beach itself. Sharks do not have a natural ability to float, so they sink if they ever stop swimming. Dr. Okihiro said the CDFW found a large amount of shark corpses because they rarely beach themselves.

Researchers are worried the parasite could spread further down the West Coast and possibly affect other species of sharks. Okihiro estimated at least 50 smooth-hound sharks, around 100 halibut, hundreds of striped bass and 500 bat rays died between February and July. According to his estimates, between 1,000 to 2,000 leopard sharks died in the bay this year, but the death toll could be higher.

Okihiro, who regularly conducts shark necropsies, and researchers at UC San Francisco discovered the common parasite plaguing the sharks. Despite these developments, the CDFW cannot devote more resources to researching the parasite.

“We have a lot of constraints on how our programs are funded,” Gabe Tiffany, Deputy Director of Administration for the CDFW, said. He did not provide details about how much money the department provides to researching the leopard shark deaths, but the CDFW later confirmed it was not funding any research. Officials at the CDFW said they will continue to use its resources for research and preservation of higher-risk wildlife.