Cutthroat dolphins on the attack in Bay Area waters

Killer dolphins bent on ocean domination could be lurking in the waters off San Francisco, preying on smaller sea creatures in what might be a classic battle over territorial rights.

Porpoise carcasses have been washing up on California shores in recent months at alarming rates, and several signs point to dolphins. A gang of young males was blamed for past deaths, according to a recent report from the Farallones National Marine Sanctuary, and experts say they are likely to blame for five August killings as well.

Click on the photo at right to see graphics of where carcasses have been found and how they died.

“Necropsies showed multiple fractures from blunt-force trauma,” the report said. “Some
porpoises had tooth marks.”

Mary Jane Schramm, a spokeswoman for the marine sanctuary, said the suspected perpetrators are a recent arrival to Northern California waters, typically living in warmer ocean climates south of the Bay Area.

“These dolphins shouldn’t be here,” she said. “They made their way north during the 1982-83 El Niño weather system and stayed ever since.” The dolphins might even be calling the entire California coast their home.

However, the harbor porpoises had not been in Bay Area waters in 65 years until fairly recently, Schramm said.

“They returned about five years ago,” she said. “They left during WWII, when there was increases in shipping in the Bay and poor water quality.”

Harbor porpoises are 6 feet in length with a round and stocky build, according to the American Cetacean Society. They eat nonspiny fish and live in colder water. Bottlenose dolphins are more than 7 feet long and eat a variety of fish, including squid and crustaceans.

Some of the victims of the dolphin attacks have been cases of mistaken identity, according to the marine sanctuary’s report. For instance, one dolphin killed one of its own calves; it was the size of a harbor porpoise. Another victim was a lactating female porpoise that was attacked in Half Moon Bay.

Jim Oswald of the Marine Mammal Sanctuary said the number of recorded carcasses in August is “certainly” more than the same month in previous years, yet he was hesitant to place blame specifically on dolphins. He said they could be one reason, but added that a variety of other reasons could contribute to porpoise deaths, such as run-ins with ships.

“It’s an animals-in-the-wild thing,” he said. “Some might have been a result of dolphin bashing, but it’s hard to say they’re responsible for all deaths. We just may never know that answer.”

akoskey@sfexaminer.com

Bay Area NewsLocalSan Francisco

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