Once, great fleets of vessels sailed from Newfoundland. Catches of salt cod supported nearly 400 schooners in each of these ports. The introduction of the steam powered trawler from England heralded a sea change in how groundfish were caught, and rapidly replaced the schooner fleets.
Courtesy NOAA

Fishing boats, Friday Harbor, San Juan Island, Washington
© Wolfgang Kaehler Smithsonian Institution

The Aleutian low pressure zone in the North Pacific drives local variations in the ocean ecosystem. The low is strongest in winter, as shown.
NOAA

Slight differences in water temperature -- "anomalies" from average -- occur at the same time as big changes in Pacific fish harvests. The relationship holds for Pacific salmon and California sardines.
Based on data by Klyashtorn and Smirnov Northeast Pacific Program

The miserable condition of many fisheries is hard to dispute. Cod boats in Newfoundland, for example, are waiting, along with their workers, for the once-common fish to rebound in the North Atlantic. Around the world, coastal fishermen are scrabbling for their share of the catch, watching with dismay as large, offshore trawlers net fish by the kiloton.

Globally, there's little room for expansion in fishing: About three-quarters of all marine fisheries are either fully exploited or already overexploited.

For years, scientists have explained the problem this way: It's the fishing, stupid. Capture too many fish -- 86 million tons of fish in 1998 -- and too few remain. (Aquaculture -- fish farms -- grew another 31 million tons that year).

Only half right
This simple arithmetic, however, is under attack by scientists who say climate and ocean conditions deserve a seat at the table -- or a term in the equations, at any rate. They argue that changes in climate -- whether natural or due to global warming -- affect ocean temperatures, currents, and fertility, which, in turn, affect fish populations.

Climate is critical to the productivity and species mix of earthly ecosystems, notes Richard Beamish, a fisheries biologist in British Columbia, and likewise beneath the ocean. "There's evidence that natural fluctuations occur and are significant, and that overfishing tends to collapse fisheries when it occurs at the same time as the natural decline."

Beamish has correlated changes is fish abundance in the Northeast Pacific to the Aleutian Low, a low-pressure system near the Aleutian Islands. During winter, the intense low causes strong storms that stir up the ocean. Changes in temperature and fertility ripple outward, altering fish abundance far across the ocean.

The possibility that conditions in the ocean ("ocean regimes") might affect fish abundance has been around for several decades. During the 1980s, Beamish and a few other scientists began correlating fish numbers to ocean temperature, showing how ocean regimes affected stuff that lives in the ocean. Today, the relationship is fairly well accepted, Beamish says.

Quick-change artist
Although many people view climate as stable, Beamish insists ocean regimes can pull a presto-chango. "All of us were brought up ... to think of climate trends as being slow, glacial." Ocean regimes and ocean productivity, he says, can change within months.

That rapidity reflects fish biology, says John Magnuson, professor emeritus of limnology at the University of Wisconsin-Madison. "Fish are a curious breed of animal. Each female can produce thousands of eggs, and if conditions are right for survival, you can get explosive regrowth." In poor conditions, however, "you may get no effective survival."

The result is big swings in the number of fish surviving from particular years, Magnuson adds. "Fishermen know that some times there are lots of fish, and other times they crash."

Ocean regimes are driven by broad changes in the ocean and/or atmosphere -- particularly El Nino and Aleutian Low in the Pacific, and the North Atlantic Oscillation in the Atlantic.

"These large-scale weather oscillations in different areas of the globe affect the way the ocean works, and the production of small food organisms and the survival of young fish," says Magnuson.

Out o'synch?
As the effect of ocean conditions on fish numbers sinks in, so should the idea that fish abundance will fluctuate, Beamish says. "If weather and climate affect fish, and if cycles affect weather, it follows that cycles affect fish abundance." These cycles vary from one to several decades in length, echoing the weather pattern driving them.

Unfortunately, as Magnuson observes, the fishing industry has its own cycles, and they are not in synch with the fish. "When fish are very abundant, people fish, buy boats," he says. "Then, when the large-scale regime shifts and productivity starts to decrease, it's been very difficult for commercial fishermen to reduce their fishing effort."

Call it overfishing.

That's apparently what happened to the Pacific sardine fishery earlier in the century. These slippery little numbers were canned by the gazillion at Cannery Row in Monterey, Calif. In the 1930s and 1940s, as John Steinbeck gathered material for "Cannery Row" along the docks, the sardine population crashed, taking down the picturesque canning operations. Scientists who study ocean regimes attribute the crash to heavy fishing pressure -- and the Aleutian Low. The climate-fish relationship is not always obvious. Diego Holmquist, a graduate student in fisheries at the University of Washington, counted fish scales in sediments along Vancouver Island, Canada, and used climate estimates from tree-ring data.

Maintaining Atlas TOGA-TAO buoys on the equatorial El Nino array. Personnel off the NOAA Ship RONALD H. BROWN. These buoys are instrumented to measure ocean temperature at varying depths and give forewarning of El Nino or La Nina events.
Photo by Lieutenant Mark Boland NOAA

Fish heads
Fish seemed only weakly related to fish numbers, possibly due to "noise" in the data. Holmquist did, however, notice a relationship between anchovy numbers and wind. Wind along Vancouver Island causes deep water to well up, fertilizing plants and increasing ocean productivity.

When the wind is weak, the anchovies are hungry -- and scarce -- due to the lowered fertility. When the wind is strong, it pushes fish away from the coast. So anchovies -- like philosophers -- thrive at the golden mean, when winds are moderate and their gullets are full.

As the effects of climate emerge, they are starting to play a role in fishery regulation. An appreciation of climatic cycles is critical to sustainable harvests of high-quality protein. "We need to have faith in the way the system operates," says Magnuson, "and maintain a strong capability to restrain fishing during decreasing productivity -- or to encourage it when the fish come back." Canada is already eyeing the Aleutian low while managing halibut around British Columbia, he adds.

Fish tails
Could climate and ocean regimes get too much blame for declining fisheries? Perhaps. There's always a tendency to blame nature for our transgressions. But advocates of the new understanding don't downplay overfishing. "I'm not saying that fishing is unimportant," Beamish explains. "I'm saying that fishing and climate change are both important."

Cycles, he concludes, are "a major concern in fish management. You either deal with them or find the evidence to say they're not important."

The surprising ecological impact of overfishing.