Researchers are trying to figure out why hundreds of leopard sharks have been washing up dead the past 13 weeks on the shores of the San Francisco Bay.
The San Francisco Chronicle reports fish pathologist Dr. Mark Okihiro released findings on Wednesday that show a common pathogen was in three sharks examined so far.
The mass die-offs, the epidemic has spread to other parts of the San Francisco Bay.
There have also been several reports of dead sharks, rays and fish washing up on beaches near the Golden Gate Bridge.
Sean Van Sommeran, executive director of the Pelagic Shark Research Foundation, believes the source of the infections is the city’s use of tide gates near inland waterways.
Leopard sharks come into shallow waterways to mate during the spring and summer, so they often get trapped when the tide gates close.
When the gates reopen, the rotting and decaying sharks are released back into the bay, where Van Sommeran fears they could be contaminating more animals.
In addition to spreading geographically, Van Sommeran has seen more species being affected in recent weeks.
“Last week a sevengill shark washed up near Oakland, just east of the airport. In addition, sturgeon have washed up, halibut, striped bass and flounder-type fish.
The stranding of a sevengill shark is especially significant, according to Van Sommeran, because the sevengills dwell deeper than leopard sharks.
If sevengills are also being sickened and killed, it could indicate the scope of the infection is larger than originally thought.