Hundreds of dead sharks washing up on Bay Area shores

For seven weeks straight, hundreds of sharks have been washing up dead on the shores of the San Francisco Bay.

Sean Van Sommeran, executive director and founder of the Pelagic Shark Research Foundation, says he's been getting calls daily since March of reported sharks washed up along the waterways of San Mateo County, Alameda and even Lake Merritt.

"We cant actually keep up with the volume of calls we get on a day-to-day basis," Van Sommeran said.

Several types of marine life have been turning up dead, including rays and large fish like halibut. But primarily, Van Sommeran has been seeing hundreds of leopard sharks washing up. He estimates the number of dead and dying sharks in the bay could be in the thousands.

"This is just the tip of the iceberg," Van Sommeran told SFGATE. "We're only seeing a fraction of the actual losses."

Over the past seven weeks, the Pelagic Shark Research Foundation has responded to hundreds of reports of washed up leopard sharks. Over the past seven weeks, the Pelagic Shark Research Foundation has responded to hundreds of reports of washed up leopard sharks. Photo: Pelagic Shark Research Foundation Photo: Pelagic Shark Research Foundation Image 1 of / 9 Caption Close Hundreds of dead sharks washing up on Bay Area shores 1 / 9 Back to Gallery

Van Sommeran's years of research have led him to believe the explanation for the recent spike in stranded sharks can be found in Redwood City. "That appears to be the epicenter of all these incidents," he said.

The researcher explained it all comes down to the city's use of tide gates in residential areas near inland waterways. To keep from flooding during the rainy season, Redwood City closes its tide gates during low tide. That way, when there are heavy rains, the extra precipitation doesn't combine with high tides to flood homes along the water.

The problem, according to Van Sommeran, is that leopard sharks come into the shallow waterways to mate and pup during the spring and summer, so they often get trapped when the tide gates close.

The storm runoff that fills the waterways isn't good for sharks' health in any case, but years of drought followed by an extremely rainy season have exacerbated the damage. "During drought, stuff that would usually get washed away congeals and backs up," Van Sommeran explained in an interview. "So with the hard rain there's extra crud going into the watershed."

The stagnant water in these inland waterways quickly goes foul (just like a home aquarium would if not regularly cleaned) and sickens the sharks. "The water becomes toxic and the sharks can't cope with it," Van Sommeran said.

When the tide gates reopen, the rotting and decaying sharks are released back into the bay, where Van Sommeran fears they could be contaminating more animals.

While this isn't the first mass stranding of leopard sharks in the San Francisco Bay (The San Francisco Chronicle reported on a spike in 2011), the full extent of this most recent die-off may still not be known.

Van Sommeran argues this is a major conservation issue that is being overlooked. He said, "It's definitely a recognized environmental issue for San Francisco, which is otherwise known to be exemplary in that area."