Shark Stewards is assisting the Department of Fish and Wildlife and the Pelagic Shark Research Foundation investigating the die off of sharks and rays in the San Francisco Bay. Since April, hundreds of sharks and rays have been reported washing ashore inside the San Francisco bay, believed to be associated with a number of factors affecting water quality.

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Dr. Mark Okihiro, a pathologist with the California Department of Fish and Wildlife has identified a fungal disease that could be the cause of deaths of hundreds of these sharks throughout the Bay. Believed to be associated with the high rainfall and low salinity, and contaminants running into the Bay, the die off coincides with the period when Bat Rays (Myliobatus californica and Leopard Sharks (Triakus fasciata) enter the shallow regions to give birth. These sharks are adapted to estuarine conditions and normally are tolerant to salinity changes. However, flood control and entrapment in water basins off Redwood city, Foster City and the Berkeley Aquatic Park and contaminated runoff are likely exacerbating conditions locally.

Shark map

One Region of Dead Shark Recovery. Credit Dr. Mark Okihiro CA Dept. Fish and Wildlife

In 2011 more than 1,000 dead sharks were counted along the Redwood Shores Lagoon and along Richardson Bay, in Marin County in the last major die off.  However, recurring die off events including entrapment in flood control basins or artificial lagoons have been recorded in the Bay, including one in Berkeley in 2016.  Given that elasmobranches do not have swim bladders and will when dead, the impact on the population can be more significant than observed from stranding data. City managers and public works have been alerted in Foster and Redwood Cities, and the State Regional water Quality Control Board has been asked to investigate  the South Bay water quality in lagoons and containment basins.

Shark Stewards is working in the East and North Bay to collect samples and observations and our Shark Watch program collects observations of live sharks on iNaturalist. Contact us with a sighting or the PSRF.

Leopard shark pathology

Diagram infested region. Credit Dr. Mark Okihiro CA Dept. Fish and Wildlife

petrei dish

Cultured Fungus From Dead Leopard Shark Credit Dr. Mark Okihiro CA Dept. Fish and Wildlife

Leopard Shark Brain

Infected Brain from Recovered Specimen. Photo Credit Dr. Mark Okihiro, CA DFW

If you see a stranded shark or struggling animal in the shallows of the Marin and San Francisco County please contact us with location and a photo if you are able.