Deaths of Dolphins Investigated

Scientists performed necropsies Friday on three dolphins to determine why more than 20 of the marine mammals have turned up dead on Southern California beaches in recent weeks.

A naturally occurring toxin may be poisoning them, said John Heyning, curator of mammals at the Natural History Museum of Los Angeles County.

Since late February, more than 22 dolphins with no signs of injury or illness have turned up on Ventura, Los Angeles and Orange County beaches, three of them on Friday morning. In a normal year, only one or two dolphins wash up on local beaches during this time.

“They look robust and healthy, except they’re dead,” Heyning said.

All have been common dolphins, which are smaller than bottlenose dolphins and do not usually swim along the shoreline.

Tissue samples will be sent to labs around the country to determine what has killed them. Results are expected next week.

The stranding is the largest in Southern California since 1994, when more than 70 dolphins washed ashore during a three-month period, said Joe Cordaro, a wildlife biologist with the National Marine Fisheries Service in Long Beach. The cause of those deaths was never determined.

This time, scientists suspect a potent toxin called domoic acid. Although it has never been identified as being deadly to dolphins, it has been blamed for the deaths of other marine mammals, including humpback and blue whales. In 1998, it killed more than 400 sea lions off the California coast.

Domoic acid is produced by naturally occurring blooms of single-celled organisms of the genus Pseudonitzschia.

The toxin is concentrated in filter-feeding animals, such as anchovies and sardines, which are in turn eaten by dolphins and other mammals.

“We’re concerned, but we’re not alarmed,” Heyning said. The overall population of common dolphins has remained stable.

The California Department of Health Services has issued a health advisory, warning the public not to eat mussels, clams, scallops, sardines, anchovies and crabs caught in the Monterey Bay region because of elevated levels of domoic acid found in those creatures.

The restrictions do not apply to commercially harvested fish, shellfish or crab.