What's killing hundreds of Leopard sharks?

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Hundreds of Leopard sharks have washed up around the San Francisco Bay Area of the U.S. since April.

A pathologist from the California Department of Fish and Game performed a necropsy on one of dozens of dead sharks found in Redwood Shores, which has seen the largest concentration of shark deaths.

The pathologist found "inflammation, bleeding, and lesions in the brain, and hemorrhaging from the skin near vents." Bleeding was also found around the shark's internal organs. However, what's causing this to happen is still unclear.

Redwood City resident Catherine Greer was fishing with her son in the area when they spotted a large number of beached Leopard sharks. They tried to push some of those that were still alive back into the water. "…they'd swim right back, thrashing their heads against the shore...as if they were trying to commit suicide", she said.

Van Sommeran, executive director of the Santa Cruz-based Pelagic Shark Research Foundation called the Department of Fish and Game’s necropsy results “startling" in what is a "pretty resistant" species. He suspects that water quality may be the cause, but tests on the Redwood Shores lagoon waters have revealed nothing unusual.

However, in a more recent report by The San Francisco Chronicle, state biologists said that heavy rain in the area may to blame, throwing the fish's body chemistry off balance by the torrents of freshwater flowing into the lagoons.

Carrie Wilson, a marine biologist with the California Department of Fish and Game said: "They might be going into these coves to pup. If there's more fresh water intrusion and low salinity, it's very tough on these animals."