What is the cause of the high number of dead leopard sharks?

The mysterious increase in mortality, among leopard sharks in San Francisco Bay, is most likely linked to increased rainfall, during the winter. Heavy rains dilute the bay’s sea water, dramatically changing conditions, according to the department investigating the matter.

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Biologists investigating the mysterious shark mortality believe that the fish’s body is thrown out of chemical balance by the freshwater streams that hit the coastal regions of the bay, where the sharks go to spawn and search for food.

“They most likely go to small bays to give birth to their young,” says Carrie Wilson, a marine biologist with the California Department of Fish and Game. “If there is more fresh water and low salinity in the areas mentioned, conditions for sharks become extremely harsh.”

Since mid-April, more than 100 have already been counted, having died of unexplained causes. This includes both juveniles and adults.

The leopard shark measures 1.2-1.5m and lives for about 40 years. It is found in a very narrow area, specifically on the east coast of North America, where it is often found in not too deep coastal waters from Oregon to Mexico.

Source: http://www.upi.com/
Photo: Bernt Rostad/flickr