Study: Commercial Whaling Caused Massive Ecosystem Decline

by Maria A. Schulz

A new scientific study published on September 22 says that commercial whaling by Japanese and Russian fleets over a half a century ago could be the cause of a mysterious, massive decline of the ecosystem surrounding Alaska’s Aleutian Islands.

The research team was led by Alan Springer of the University of Alaska’s Institute of Marine Science in Fairbanks, and James Estes, a coauthor with the U.S. Geological Survey in Santa Cruz.

For years, scientists have been debating the exact cause of devastating changes to one of the Earth’s richest oceanic ecosystems, setting in motion a chain reaction that has harmed sea mammals and kelp forests in the North Pacific and Bering Seas.

The researchers said killer whales that once preyed upon the larger "great" whales had to turn to other food sources to sustain themselves after the commercial killing of half a million bowhead, sperm, humpback and other large whales caused a collapse in the food chain.

According to the study, the killer whales (also known as "orcas") first turned to seal, and then when seals became less plentiful, they turned to Steller’s sea lions. When those mammals also grew rare, the killer whales turned to otters.

Without otters to eat them, sea urchins seized their chance to proliferate. The sea urchins, spiny round blobs, have now begun to eat right through the underwater kelp forests that house many different life forms along the ocean floor.

"If our hypothesis is correct, either wholly or in significant part, commercial whaling in the North Pacific Ocean set off one of the longest and most complex ecological chain reactions ever described, beginning in the open ocean 50 years ago," said the scientists in their report, published online in the Proceedings of the National Academy of Sciences.

They said the chain reaction is still continuing, with the devastation of huge kelp beds off western Alaska.

Sea lions have declined by more than 80 percent in the last 30 years throughout a huge area that stretches from Alaska to Japan, according to the National Marine Fisheries Service.

Harbor seals, fur seals and sea otter populations have also been decimated in most areas of the North Pacific.

Some scientists believe that commercial fishing has depleted coastal food resources, leading to malnourished populations that are susceptible to diseases.

Others believe global climate changes have so altered the ocean that these animals are finding it hard to survive.

But Springer, an oceanographer, found these theories hard to accept.

So, he contacted Jim Estes, the author of a report that claimed that killer whales were to blame for the decline of sea otters in the Aleutian Islands.

"Jim had come to the conclusion, based on a lot of really thorough research in the Aleutian Islands, that predation was the most probable explanation for the collapse of the sea otter population," Springer said.

The pair was joined by six other scientists, who discovered that the collapse of other sea mammal populations could have been caused as a result of killer whales turning to other sources of nutrition following the disappearance of the great whales.

Now, years later, the dietary preference of killer whales may have changed forever.

The study determined that a shift in diet among less than 1% of the region’s estimated 3,900 killer whales would have been enough to cause the declines in the mammal populations.

The new killer whale diet is not sustainable. The big whales provided sixty-fold more biomass than the combined totals for seals, sea lions and otters, according to the report.

"The message," said Springer, "is that over-fishing and massive extraction can lead to food impacts that are unexpected and unintended."

© 2003 Animal News Center, Inc.