Marine Biologists Are Puzzled by Mysterious Deaths of Sea Otters

Marine biologists are scrambling to discover why California sea otters, the fuzzy, brown-eyed darlings of the Monterey Bay, are declining rapidly.

A fall survey found the sea otter population between Santa Cruz and Point Conception had dropped 12% from one year earlier, pushing the already federally protected species closer to endangered status.

Since then about nine a month have been washing up on beaches.

Although the state’s top sea otter experts have found no definite cause, they say the blame may lie with fishermen using crab pots in the thick kelp forests that sea otters call home.

California’s fishing industry is indignantly denying that their members are in any way responsible. In fact, the group contends that the otter aren’t even at risk.

“There’s absolutely no proof that a sea otter in California has been harmed by any commercial fishing operation since 1986,” said Diane Pleschner, manager of the California Seafood Council. “It’s just typical of the Fish and Wildlife Service to justify their position of expanding sea otter populations at all costs.”

In recent weeks, marine biologists have clipped tracking devices into the flippers of some juvenile sea otters to follow them. They have performed necropsies on the dead otters and placed various fishing equipment near otters to see if it is causing them harm.

“We could say, ‘Oh well, don’t worry, so they’re declining.’ But then they could be gone and it would be too late and other species could start dying too,” said Krista Hanni, a UC Davis epidemiology doctoral candidate.

Standing above the crashing waves of the Monterey Bay, Hanni pointed a large, hand-held antennae toward the Pacific Ocean, searching for an otter she is tracking.

“These deaths are like a ball of string that needs to be unraveled before it is too late,” she said.

The fall count along about 200 miles of coastline showed 1,937 otters, just above the 1,850 mark under which they could be listed as endangered. Several years ago, southern sea otters numbered well above 2,000 and neared 2,650, the figure at which they’d be considered as recovered and taken off the threatened list.

Marine biologists have yet to solve the riddle of their decline, but so far they say it seems likely that the cause is the increasing West Coast use of a traditionally East Coast fishing technique: pot fishing.

Commonly used by lobstermen and crab fishermen, pots are constructed either of wooden slats or, more commonly, coated wire mesh. They are set on the bottom individually or in strings and harvest various species of shellfish and finfish in kelp forests.

During recent experiments with captive otters at the Monterey Bay Aquarium, the curious creatures meandered into the pots and got stuck.

Jim Estes, a U.S. Geological Survey wildlife biologist, said that this is a preliminary theory, and that more work must be done to determine if, in fact, the pot fishing is responsible. But so far, he said, it seems like the best theory.

“The fishermen aren’t going to tell us about this, but we’ve heard rumors that the otter are being killed in these pots,” Estes said. “There’s a fair number of boats involved in this.”

Other theories about the increased deaths include disease or lack of food. But Estes said about 40% of the otters found dead on shore have always had some sort of infection. And he said sea urchins and other shellfish eaten by the otter seem plentiful this year.

In an unrelated problem, northern sea otter populations among some of the Aleutian Islands have decreased 65% to 90%. Those deaths are being pinned almost entirely on killer whales.

At the California Seafood Council, Pleschner said the scientists are completely misguided. She said that the drop in the California count can be attributed to El Nino weather patterns, and that the spring survey will show that the populations have recovered.

“The animals are not going extinct in any way, shape or form in California,” she said. “That’s baloney. We have a healthy and thriving population.”