Major shark die-off in San Francisco Bay? The California Department of Fish and Wildlife revealed that as many as 2,000 leopard sharks have died in the San Francisco Bay over the past few months. But, they said that due to limited resources, they won’t be able to fully research how to stop the cause of these die-offs.

NBC Bay Area investigated the CDFW’s findings, speaking with Dr. Mark Okihiro, a research scientist with the CDFW. According to him, the department believes a pathogen or parasite is the most likely cause of death. He also explained why, after months of die-offs, this particular parasite is a problem. He said, “This year is unusual in that there has been a large number of other species that have also been dying. This pathogen can tackle a variety of different species … we’ve had a much more diverse group of fish that have been found dead in the San Francisco Bay.”

After much research, Dr. Okihiro found a specific parasite that was common amongst all shark deaths in the Bay. “We’re pretty confident at this point,” he said. “It’s called Miamiensis avidus… it’s a small single celled organism. It’s very similar to the common amoeba.” He went on to describe how the parasite attacks the shark’s brain, swimming up through its nose and slowly eating away at it. Eventually the shark succumbs to the parasite and either ends up swimming in circles aimlessly or they end up beaching themselves. In any case, if a shark ever stops swimming, it sinks to the bottom of the ocean — they’re not naturally buoyant. That’s where the CDFW has found the vast majority of shark corpses, since only a small fraction of sharks that fall victim to the parasite end up beaching themselves, explained Dr. Okihiro.

There’s a significant worry that this parasite could spread farther along the West Coast, and that it could also potentially affect more species beyond leopard sharks, as Dr. Okihiro said. But the CDFW is unable to dedicate resources to researching this parasite. Gabe Tiffany, Deputy Director of Administration for the CDFW, explained that the department is just straight up strapped for resources right now, saying, “We have a lot of constraints on how our programs are funded.”

Deputy Director Jordan Traverso also went on to break down just where the department’s priorities lie right now. He said, “Some of the current priorities include implementing the Marine Life Protection Act and establishing and monitoring Marine Protected Areas, rebuilding impacted fisheries (Chinook salmon in-river and the ocean, red urchin, red abalone), addressing the kelp die-off along the north-central and north coast, and implementing a different water management scheme to provide healthier fish populations in the Central Valley rivers, Delta, and San Francisco Bay.”

On top of dealing with all of those issues, the CDFW is currently dealing with a lawsuit filed by an environmentalist group who is accusing them of being responsible for the deaths of endangered or threatened whales. In their lawsuit, the Center for Biological Diversity argue that their responsibility stems from the fact that the CDFW authorized and managed a fishery that used Dungeness crab pots, which later got loose and ended up getting tangled up with passing whales. An NOAA report revealed that at least 21 whales died as a result of these entanglements.

Despite all this, Dr. Andrew Nosal, a marine biologist at UC San Diego, warned that the shark die-offs are a “canary in a coal mine,” and urged the CDFW to take action. He said, “When they die and wash ashore, it’s pretty obvious. We see it. But what about all the other species that, perhaps, are getting sick and dying and simply sinking to the bottom that we just don’t know about? There’s a lot more at stake here than just leopard sharks.”


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