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

By Cameron Walker
for National Geographic News
January 9, 2003
Sardines and anchovies swim to the beat of a 50-year climate cycle in
the Pacific Ocean. The seesawing changes of these two tiny fish—the
one abundant when the other is scarce—have highlighted a natural
climatic pattern that may color our understanding of global warming.

While scientists have known that sardine populations along the California coast took big swings based on changing ocean temperatures, the study that appears January 10 in the journal Science spots an ocean-wide pattern behind these fishy fluctuations.

"Different people were talking about these cycles in their part of the ocean," said Francisco Chavez, a biological oceanographer at Monterey Bay Aquarium Research Institute (MBARI) and lead author of the paper. When Chavez's team pulled together 100 years of research from around the Pacific Rim, the sardine's boom-and-bust cycle kept reappearing. And around the ocean, anchovy populations stepped up as sardine levels sank.

"They were all marching to the same drummer," Chavez said.

Fishing for Climate Changes

Chavez and John Ryan of MBARI, along with researchers from Mexico and Peru, piled up a range of evidence to get to the bottom of this piscine pattern. The team checked fish catches, temperature measurements, ocean current records, and carbon dioxide concentration in the atmosphere. They looked at other species, such as anchovy-swilling seabirds, that might provide clues to changing fish numbers.

By using everything from high-flying satellites to seaworthy vessels, the researchers spotted a likely culprit that could sway fish populations: a naturally-occurring climate pattern that works its way across the Pacific.

This 50-year cycle resembles the El Niño events that take place every three to seven years. Along the eastern Pacific, sardine success starts when coastal waters surrounding California and Peru warm up, a pattern similar to El Niño's warming ways. And while scientists had spotted this cycle, known as the Pacific Decadal Oscillation, no one had tailed its influence across an entire ocean.

When things heat up, warm surface water traps nutrient-rich cold water in the deep spots. The nutrients feed phytoplankton, which becomes prime pickings for larger sea species. Decreasing levels of this smallest marine meal can tinker with a host of marine species, including the anchovy.

Schools of sardine and anchovy seem to switch off every 25 years, following rounds of warming and cooling ocean temperatures. During the mid-1970s, the warming Pacific sparked a "sardine regime." In the middle to late 1990s, the cycle swung the other way. Surface water cooled and anchovies started to return.

Chavez said natural warming and cooling like this may be missed when tallying climate change. "I worry a little bit that these fluctuations are confused with global warming," he said. The warming trend in the mid-1970s that ushered in a new batch of sardines came about the same time concern rose about global warming.

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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