Fisheries Ebb and Flow in 50-Year Cycle, Study Says

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Those trying to take the planet's temperature need to look at climate on a long-term scale to avoid the influence of natural cycles, Chavez said. If the trends reverse themselves, the warming may be part of a natural pattern. "If they keep going, we know certainly that this is global warming, or at least a longer cycle," he said.

Studies of long-term climate cycles help fine-tune understanding of global warming by eliminating "noise in the signal," said Frank Schwing, an oceanographer at Pacific Fisheries Environmental Laboratory in Pacific Grove. "We may at some time in the future find ourselves in a permanent 'sardine regime' or another less welcome state."

Something's Fishy in Monterey

Monterey Bay was one of the victims of this swinging pendulum. In the late 1930s, the sardine canneries boomed, with the tightly packed fish supporting the biggest fishery in the Western Hemisphere. John Steinbeck's book Cannery Row detailed the after-hours life surrounding this oceanfront industry.

By the 1950s, these silver fish had pulled a slick disappearing act. The annual catch sunk from 3.6 million metric tons (4 million tons) during 1934 to less than 10,000 metric tons (11,000 tons) in 1965. The canneries shut down and left empty nets and warehouses in their wake. Further south, another fishery suffered through the same highs and lows. While the sardine canneries failed along the California coast, anchovy business picked up in Peru, where the world's largest single-species fishery cranked in Peruvian anchoveta catches from the 1950s to the 1970s.

Some have blamed intense fishing for the crash of these booming catches.

But in looking at fishing catches from around the Pacific, Chavez's team saw that sardine populations had shrunk on both sides of the ocean. Then, in the late 1970s, the sardines started to return. In 1999, scientists declared the Pacific sardine resource off California to be officially "recovered."

"I'm not saying don't be worried about overfishing, just that some of these events—like the one in Monterey—were caused by this cycle," said Chavez.

David Checkley, a biological oceanographer at Scripps Institution of Oceanography, said that sardines and anchovies have been undergoing ups and downs throughout the last two thousand years. "These fluctuations existed prior to fishing," he said. "Fisheries cannot be implicated as the sole cause of the fluctuations in the past 50 years."

The relationship between anchovies and sardines may not be so simple, he said. The two fish have mirrored each other in the past 50 years, but over longer periods, their populations haven't lined up as easily.

Although many questions still remain about the climate cycle and its effect on fish, understanding the ocean's patterns can help fisheries stay afloat. In Japan, the sardine catch is on the downswing. "However, it continues to be fished rather heavily, most likely accelerating its rate of decline," said Checkley.

Past crashes in Monterey and Peru, along with studies like this, underscore the ebb and flow of the sea's spoils. "We now realize that living marine resources are not constant, and must learn to manage them accordingly," said Schwing.

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