Study takes historical peek at plight of ocean ecosystems

Jane Kay Chronicle Environment Writer

07/26/2001 The San Francisco Chronicle FINAL A.4 (Copyright 2001)

Overfishing and hunting of marine mammals over past centuries set the stage for the current collapse of coastal ecosystems, say scientists in a major new study based on records dating back 125,000 years.

In one of the first studies to take a historical look at the problem, the researchers found that fishing by aboriginal cultures and European colonialists contributed to the extinction or severe depletion of many marine species.

Among the species cited by the study are whales, manatees, sea cows, monk seals, crocodiles, swordfish, codfish, sharks and rays.

The study, released today in the journal Science, was conducted by researchers at the Scripps Institution of Oceanography, the U.S. Geological Survey and the University of California, among others.

"Contrary to romantic notions of the oceans as the 'last frontier' and of the supposedly superior ecological wisdom of non-Western and precolonial societies, our analysis demonstrates that overfishing fundamentally altered coastal marine ecosystems during each of the cultural periods we examined," said the study, whose lead author is Jeremy B. C. Jackson, a marine biologist at Scripps in La Jolla (San Diego County).

"Human impacts are also accelerating in their magnitude, rates of change and in the diversity of processes responsible for changes over time. Early changes increased the sensitivity of coastal marine ecosystems to subsequent disturbances and thus preconditioned the collapse we are witnessing," they said.

Hunting and fishing of the oceans came in three distinct but overlapping periods: the aboriginals starting about 10,000 years ago, the European colonialists trading in whale oil and marine mammal skins, and the recent global expansion using sophisticated technologies and "factory" trawlers.

Coastal species were suffering from overfishing even before other man-made problems, such as pollution, eutrophication (lack of oxygen leading to toxic algae blooms), physical destruction of habitats, diseases, invasive species and climate change, the study said.

This is one of the first historical looks at overfishing, offering a comparison between a vastly abundant sea life found in marine sediments dating back 125,000 years and present day impoverished populations that depend on damaged kelp forests, coral reefs and seagrass beds.

Until now, scientific understanding has been hampered by mainly local, short-term studies conducted after the 1950s. These studies also didn't consider the ocean conditions relating to changing temperatures and other climatic events.

The collapse of ecosystems often occur over a long period.

In one example, when Aleut hunters killed the Alaskan sea otter about 2,500 years ago, the population of their natural prey, the sea urchin, grew larger than its normal size. In turn, the urchins grazed down the kelp forests, important habitat for a whole host of ocean life.

Then, when fur traders in the 1800s hunted the otters and sea cows almost to extinction, the kelp forests disappeared and didn't start to regenerate until the federal government protected the sea otters in the 20th century. In California, the diversity of spiny lobsters, sheephead fish and abalone kept down the urchin numbers.

At present in Alaska, the kelp beds are declining again in areas where killer whales are preying on sea otters. Biologists think the killer whales switched to otters for food because there are fewer seals and sea lions to eat.

The reasons seal and sea lion populations have dropped are still unclear, according to one of the authors, U.S. Geological Survey marine biologist Jim Estes.

"One possibility is overfishing," Estes said. "The fishers took food the seals and sea lions would have eaten. A second could be a less productive ocean, with less food for the seals and sea lions in the North Pacific, related to ocean warming, perhaps cyclical or part of a larger human-caused trend. A third possibility is predation by killer whales or other predators."