Scientists Find Ancient Salmon Cycles

“The neighbor lakes were very constant and not changing very much over time relative to these salmon lakes where we see these dramatic changes,” Finney says.

Triggering a Ripple Effect

The researchers then compared the years of high and low runs with meteorological records and found a consistent match with variations in the climate. Warmer weather resulted in stronger runs, Finney says, but not necessarily on a year-to-year basis. The statistics apply to decades-long changes, so one warm winter does not necessarily mean high salmon runs the following summer.

Furthermore, he adds, it’s unlikely that changes in temperature alone account for the boom and bust cycles.

“I don’t really think it’s the temperature itself that’s doing it,” Finney says. A more plausible explanation, he says, is that temperature changes cause a ripple effect, altering oceanic circulation patterns, and probably the abundance of nutrients that are so vital to salmon survival. But nobody knows for sure, Finney says.

“One thing the research points to is we really don’t know how the ocean works,” he says.

Other variables, including human intrusion, also play a major role. The researchers found evidence in five Alaska lakes on Kodiak Island and near Bristol Bay that fishing practices can have a devastating impact on salmon runs. Aggressive commercial fishing began in that area around 1882 and peaked at nearly four million fish a year. But by the 1970s, the harvest had diminished to about 100,000 due to poor salmon runs.

The lowered runs meant less nutrients in the lakes, and poorer survival of young salmon, causing yet another ripple effect.

For the last couple of decades, the state of Alaska has maintained strong controls over the fishery, limiting the catch so that enough salmon can “escape” up the rivers to sustain the run. Finney says his research confirms that the escape rate has been effective, keeping the salmon population in the lakes relatively constant.

But he is concerned about the future.

Salmon Bust on Horizon

Alaska, for example, has experienced a salmon boom in the past decade and commercial fishers have invested in expensive boats in expectation that the runs will continue to be strong. But the research shows that no boom lasts forever. Someday, the bust will be back. Relatively low returns the last couple of years suggest that it may already be here.

That will put enormous pressure on resource managers to allow more salmon to be taken in an effort to head off a financial crisis for the fishery.

But Finney’s research, published in a recent issue of the journal Science, indicates there will be hard times ahead for many fishers, and relaxation of management goals would only make matters worse.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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