UNDIAGNOSED DIE-OFF, SHARK - USA: (CALIFORNIA)
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Date: 21 Apr 2011
Source: San Francisco Chronicle [edited] <http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/04/22/BAK71J5IFB.DTL&tsp=1>
At least a dozen leopard sharks have been found dead or dying within the past several days in Bayfront lagoons in Redwood City, putting local researchers on alert for some kind of infection or toxic discharge in San Francisco Bay.
The deaths, including both juvenile and adult sharks, appear isolated and far less serious than previous die-offs in 2006 and 2007, which left shark carcasses strewn all over the bay, officials said. Shark experts fear there may be more of the strikingly patterned creatures floundering in Bay Area waterways and succumbing to pollution and disease.
"In the last decade, we've seen an increase in the animals trapped in culverts and pumps that used to be tidal canals or poisoned by periodic pollution events," said Sean Van Sommeran, executive director of the Pelagic Shark Research Foundation, a Santa Cruz group that tracks sharks in Monterey and San Francisco bays.
Beginning Monday [18 Apr 2011], Van Sommeran received several phone calls from people who had seen leopard sharks stranded or dead in tide pools and sloughs just south of Foster City.
Catherine Greer and her son, Lorenzo Fernandez, were among the 1st to observe the ailing sharks. Fernandez arrived on Monday [18 Apr 2011] to go fishing at a lagoon near Seabrook Court on the east side of Redwood City and saw distressed sharks near the shore, some of them coming out of the water and seemingly gasping for air. For the next 2 days, the pair returned to find more weakened and beached sharks, around a dozen in all, ranging from 12 inches to nearly 4 feet long.
"They were resting their chins in the dirt on the shoreline, like they were trying to swim ashore," Greer said. Lorenzo "tried putting one back in the water, but it just came back and stranded itself."
Leopard sharks, which commonly grow to 5 feet long and live 40 years or more, are plentiful in the shallow coastal waters from Oregon to Mexico. They typically eat crabs, small fish and "innkeeper" worms.
But their status as bottom-feeders means their systems can become saturated with harmful contaminants like mercury, pesticides and flame retardants that sink to the bay floor. Still, they are a pretty hardy species, usually the "last to abandon an ecosystem," Van Sommeran said. "They've specialized in doing well in hard-to-live-in areas."
That's why Van Sommeran and other experts are perplexed by several large die-offs within the last 5 years. Field researcher Brandy Faulkner of Palo Alto said that in 2006 and 2007 she documented dead leopard sharks "every 10 feet" along the bay at Coyote Point and Oyster Point.
Stanford University necropsies of similar but less common salmon sharks -- which are increasingly washing ashore in California -- showed some were infected with a pernicious bacteria that attacks the brain and leads to blindness, disorientation and, finally, paralysis.
The leopard sharks observed this week showed the same problems, but the bacteria have not yet been detected in that species.
Van Sommeran theorizes that pollution may play a role. He and Faulkner point out that agribusiness giant Cargill, which operates 9000 acres of salt evaporation ponds in the southern part of the bay, had 4 spills of bittern -- a noxious salt production waste fluid -- between 2000 and 2006. State records show the company spilled 218 000 gallons of the substance in August 2006, killing about 200 fish and resulting in a fine of USD 228 000. The salinity of bittern is about 10 times that of ocean water.
Officials at Cargill were not available to comment on Thursday [21 Apr 2011].
Van Sommeran said he will continue to monitor the situation in the Redwood City area and work with officials at Stanford, the state Department of Fish and Game, National Marine Fisheries Service and US Coast Guard in an effort to figure out what is killing the sharks.
"It's not a crisis at this point," Van Sommeran said. "But we don't know what's going on for sure because no one dives for shark remains; we can only track those that beach themselves."
[byline: Kelly Zito <kzito@sfchronicle.com>]
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communicated by:
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[Sharks on the west coast of the United States have been previously diagnosed with encephalitis. This may be the same situation.
The chemical plant belonging to Cargill may or may not be involved.
We will have to wait until the investigation is complete. Furthermore, even though bittern may be high in salinity, it is not likely that it is related to the bacteria found in some of the previous shark die-offs.
Bittern is the solution remaining following evaporation and crystallization of sodium chloride from brines and seawater. It is an extremely bitter solution that contains concentrated forms of magnesium chlorides, calcium, sulfates, iodides, bromides, and the other chemical substances present in the brine. This bittern provides a commercial source of compounds of magnesium, such as magnesium sulfate and magnesium bromide.
I am unsure whether large concentrations of such a solution could affect the bay water's concentration of oxygen or affect the salt balance of the sharks. However, higher concentrations of salt would seem to decrease bacteria in the water. So results of the necropsy to learn whether bacteria or even viruses are involved will be very important.
Photographs of leopard sharks may be found at:
<http://www.elasmodiver.com/Leopard%20Shark%20Pictures.htm>. - Mod.TG
Redwood City, California can be found on the HealthMap/ProMED-mail interactive map at <http://healthmap.org/r/0KHA>. - Mod.SH]
[see also:
2007
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Bacterial encephalitis, sharks - USA (OR, WA, CA) 20070830.2862 2000
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Shark die-off - USA (Florida) 20001018.1798] .................................................sb/tg/msp/sh/ll
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