ALAMEDA, Calif. (KTVU) - People in the Bay Area are starting to notice more and more dead and dying leopard sharks washing up on beaches, especially in Alameda.
It often happens during this time of year, although marine researchers say they're not entirely sure why.
When Lorin Shain went for a walk on Alameda's Crown Beach Wednesday night, she came across one.
"We saw a 3 to 4 foot leopard shark in distress. It was up on the sand struggling. Flipping over back and forth," Shain said. By morning it had died.
It is one of what marine biologists and researchers say are about a hundred leopard sharks washing up on bay area beaches in recent weeks.
Because of bay currents, Crown Beach gets many of the carcasses.
Those familiar with the shark "die-off," as many call it, say it's been happening in San Francisco Bay for years during late spring and summer caused by a parasite in the water.
"There is a protozoan parasite that swims in the water. It infects them. Gets in their brain and makes them disoriented and they swim closer to the beach," said James Frank from the East Bay Regional Parks District.
Some years are worse than others.
2017 saw thousands of leopard sharks die which is a lot. This year could be as bad because of the wet winter.
"You have a convergence of high tides pushing them inward. The the animals are seeking inward waterways for pupping. And they run into this cloud of pathogens," said Sean Van Sommeran of the Pelagic Shark Research Foundation.
The die-off is also affecting bat rays and certain other species of fish.
"We find it alarming because we are losing so many animals especially this time of year," said Van Sommeran.
There are so many unanswered questions surrounding the phenomenon, the California Department of Fish and Game is conducting a study.
The public is urged not to try and help a struggling leopard shark.
Researchers say by the time it reaches the shoreline it is too far gone to rescue.
The die off should end by August. At least until next spring.