Unprecedented Die-Off of Leopard Sharks
in Redwood City, Calif. Bay Area
“The one thing that we do know is that the leopard sharks
are washing up dead in record numbers.”
- Sean Van Sommeran, Exec. Dir., Pelagic Shark Research Foundation
Dead leopard shark washed up on Richardson Bay beach north of Sausalito,
California. One of “an unprecedented leopard shark die-off in Redwood City,
Foster City, Coyote Bay and Richardson Bay” during the first five months of 2011,
according to the Pelagic Shark Research Foundation. Image courtesy PSRF.
May 27, 2011 Capitola, California - In April 2011, the California Fish and Game Department and the Pelagic Shark Research Foundation (PSRF) in Santa Cruz and Capitola, California, started getting phone calls about dead leopard sharks washed up on beaches. As reports increased, there seemed to be a pattern of the most deaths occurring in the San Francisco Bay regions of Redwood City, Foster City, Coyote Point, and Richardson Bay on the north side of Sausalito. The California Department of Fish and Game toxicology lab has done some necropsies on the shark bodies and discovered hemorrhaging around the internal organs and inflammation and lesions in the leopard shark brains. But so far no one understands what is killing the sharks.
Leopard sharks are strong marine creatures that grow up to five feet long. The leopard shark has smaller and more numerous red blood cells, allowing it to process oxygen more efficiently as it moves in shallow waters on the seafloor. It eats lots of crabs, shrimp, bony fish, clams and fish eggs. It's harmless to humans, but humans think leopard shark meat is excellent eating and the shark is hunted and sold fresh or frozen. The leopard shark is mostly fished in the waters off California where there was a population decline in the 1980s, but new fishing regulations a decade later reduced harvesting to sustainable levels.
However, leopard sharks living alongside human development such as the San Francisco Bay communities can accumulate pollutants such as mercury, pesticides, and polychlorinated biphenyls (PCBs) within their bodies. That's why the California Department of Fish and Game warns humans not to eat leopard sharks regularly. The irony now is that some new human industrial chemical could be poisoning the leopard shark or weakening its immune system so it is vulnerable to still-unidentified pathogens.
Richardson Bay north of Sausalito (top red circle), Coyote Point near Burlingame,
then Foster City and Redwood City are the main locations of the unexplained leopard
shark die-off since January 2011. A few bat rays were also found washed up in same areas.
Even though the first documented case of a washed up, dead shark was in mid-April, Sean Van Sommeran, Executive Director of the Pelagic Shark Research Foundation, in Santa Cruz and Capitola, California, says his office received calls about dead leopard sharks before then, so he thinks the die-off started back near the beginning of the year.
Interview:
Sean Van Sommeran, Executive Director, Pelagic Shark Research Foundation, Santa Cruz and Capitola, California: “We've gotten calls every single day for the last five months. We got a call from the U. S. Coast Guard about Redwood City having some wildlife issue and concern, so we had contact with a local resident, who put them in contact with our Stranding Coordinator Brandy Faulkner out of Palo Alto, who responded. There were sharks and they were dead.”
Dead leopard shark on beach in Redwood City and Foster City, California,
bay area where an unprecedented die-off of leopard sharks has occurred since
January 2011. All images courtesy Pelagic Shark Research Foundation.
Leopard shark dead on its back along Redwood City bay.
Image by Christine Tarkowski.
Then about a week later, it was still ongoing and in fact escalating with the count up to maybe 50 animals in just one canal and lagoon (in Redwood City). Then dead things began to appear near by Foster City on their beaches. Then subsequent to that, by week two we had animals off Coyote Point, both distressed and dead - not as concentrated as in the Redwood City area, but exhibiting similar symptoms. Nothing to indicate a spill, but definite impacts on the animals behaving distressed, swimming upside down.
By then, California Fish and Game had finally responded. Their initial effort to respond was kind of curtailed abruptly by the existing budget constraints. There is a travel ban, in fact, and so we went on with the investigations where we would secure specimens on site and then ship them to the lab in Southern California. It could be a number of events happening separately, or it could be whatever happened in Redwood City being released from there and then it seems to go from there to Foster City to Coyote Point and then Richardson Bay on the other side of Marin on the north bay. That's been the focus of this over the past two weeks - not as concentrated as Redwood City and more scattered out - but the same symptoms and results of there being dead sharks on the beaches.
Bat ray dead on Redwood City beach, one of a few
found during the large leopard shark die-off.
Initially it involved bat rays as well, but as it moved beyond Foster City, we haven't seen any bat rays - just leopard sharks. So we're trying to figure out why just leopard sharks. Leopard sharks are typically the last things to get that kind of infection. They are very tolerant to various salinity levels and temperatures and low oxygen and all that stuff that estuarine sharks need to cope with. This is hitting them really abruptly. They are not emaciated. They are fully healthy animals that apparently in a very brief period of time get infected, become immobilized and short circuit all their nerves and internal organs begin to hemorrhage. So, it's weird!
No comments