Porpoise deaths unexplained off California waters

A dead California Gulf Porpoise, also known as a vaquita, is seen in San Felipe in this file picture taken February 15, 1992. A wave of porpoise deaths in Northern California has puzzled scientists and more of the dead mammals may wash ashore onto beaches in August, animal researchers said on Sunday.

SAN FRANCISCO (Reuters) - A wave of porpoise deaths in Northern California has puzzled scientists and more of the dead mammals may wash ashore onto beaches in August, animal researchers said on Sunday.

At least 24 harbor porpoises have been discovered dead and washed ashore since May, according to the Marine Mammal Center. While scientists have diagnosed pneumonia, asphyxiation, trauma, malnutrition and maternal separation as reasons for death in most cases, eight deaths are still unexplained.

"This is the time period every year where we do see porpoises and dolphins washed up ashore, it does happen," said Jim Oswald, a spokesman for the Mammal Center in Sausalito, across the bay from San Francisco. "There are a few more numbers this year."

Researchers are testing those carcasses for domoic acid poisoning from toxic algae in Pacific waters, which can cause neurological damages, such as seizures, in marine mammals.

The center has studied the toxic algae issue since 1998, and learned that sea lions can pass along the poison to their unborn fetuses.

"We want to take a look and see if that's possible (in harbor porpoises) -- is that occurring here?" Oswald said.

The National Marine Fisheries Services cites 13 harbor porpoise deaths last year and 26 in 2006.

The Marine Mammal Center rescues up to 800 ill, injured or orphaned marine mammals annually along the California coast and returns them to the wild after rehabilitation.

Harbor porpoises, which are related to whales, stay relatively close to shore as they feed in shallow waters on fish, squid and crustaceans. They are found in North Pacific and Atlantic waters off the United States.

In 2003, the National Marine Fisheries Services investigated the stranding of 11 harbor porpoises following Naval sonar exercises in Washington state, but did not find evidence of acoustic trauma linked to those operations.

Five of those animals died of blunt-force trauma or illness, the investigation found, but the remaining six deaths could not be explained.

Last year, the World Wildlife Foundation and the Whale and Dolphin Conservation Society published a report that said the rising temperature of oceans due to climate change was a threat to marine mammals -- from the increased likelihood of toxic algae in waters; to lower populations of krill, a key source of food for these mammals; to lower rates of conception.

That is in addition to the numerous threats the various species already face, the report found, from pollution to ensnarement in commercial fishing nets.

(Reporting by Alexandria Sage; editing by Mohammad Zargham)