Ecosystem Decline Tied to Whaling

Scientists for years have been debating the cause of massive and abrupt ecological changes surrounding Alaska's Aleutian Islands, where the Pacific meets the Bering Sea.

A team of scientists, led by Alan Springer of the University of Alaska's Institute of Marine Science in Fairbanks, now theorizes that the ecosystem collapse has its roots in the late 1940s, when Japanese and Russian whalers began using modern hunting techniques. At least half a million bowhead, sperm, humpback and other large whales were harvested in the North Pacific before commercial whaling ended in the 1970s.

Springer, an oceanographer, believes that pods of killer whales used to hunt the giant whales, and when whaling crews reduced their populations, the killer whales were forced to turn to other prey. They moved down Alaska's aquatic food web, devouring seals, then sea lions and then sea otter populations, which, in turn, led to dramatic shifts in life 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," the team reported in the Proceedings of the National Academy of Sciences.

The Aleutian Islands ecosystem is entirely different today than a few decades ago. Fur and harbor seals began disappearing in the 1970s, followed by Steller sea lions in the 1980s, then sea otters in the 1990s. As the otters disappeared, the sea urchins that they fed on proliferated, wiping out thick kelp forests that used to stretch 20 feet high.

The region had been a stronghold for marine mammals, and the scope and pace of the declines caught marine experts by surprise. Killer whales, the ocean's top predators, are the only mammals still thriving there.

James Estes, a coauthor with the U.S. Geological Survey in Santa Cruz, has studied the Aleutians' sea otter population for more than 30 years, and was shocked in the early 1990s as their numbers dropped abruptly and kelp forests disappeared.