Predicting salmon runs is tricky task

Fish forecast flounders in 2006

Posted: Friday, February 17, 2006

At the end of a winding maze of hallways deep in the heart of the Alaska Department of Fish and Game’s Soldotna offices, research biologist Mark Willette toils in relative obscurity. But although Willette may not be well known to many people outside the department, his work impacts nearly every commercial fisherman in Upper Cook Inlet.

Willette is responsible for coming up with the annual salmon return forecast for UCI, a number used by fishermen and biologists alike to plan for the upcoming season.

In order to come up with each year’s prediction, Willette must sift though mountains of data, including past year’s returns and historical data, conditions on the open ocean and the size of salmon fry that left the area more than half a decade ago.

And that’s a simplified description of his work.

Some of the information used to come up with the forecast, such as the size and number of salmon fry which left for the ocean three to five years ago, is data that easily can be collected and quantified. Other information, however, such as salmon survival on the high seas, is more guesswork related to ocean currents and temperatures.

Also taken into account is the cyclical nature of salmon returns, something that played a big factor in Willette coming up with a 2006 forecast that calls for a below-average return of sockeye to the upper inlet.

“We’re basically in the low end of that cycle,” he said.

Willette explained that in 2001, a smaller-than-average number of fry were counted leaving for the ocean. Because 5-year-old salmon make up the majority of the run, he was led to make a prediction that calls for a return of approximately 3.6 million sockeye.

The biggest factor in predicting run strength has to do with fry counts made when juvenile salmon leave freshwater for the open ocean. These counts are done by biologists, and the numbers fed into complex models that give biologists an idea of how many of those fish will live long enough to return and spawn as adults.

Predictions relating to how many salmon will return are only guides and not an absolute guarantee of how many fish will, in fact, return. In 2005, for example, Willette estimated a return of 3.3 million sockeye to the Kenai River and a commercial harvest of 4.1 million sockeye in Upper Cook Inlet. Those numbers turned out to be on the low side, as more than 5 million sockeye streamed back to the Kenai, with commercial fishermen harvesting more than 5 million — their third-largest harvest on record.

Willette said last year’s run likely reflected good survival rates for fish in the open ocean.

“It appears marine survival has been above average for the last few years,” he said.

Whether favorable conditions on the ocean will again lead to a larger-than-expected return of salmon this year won’t be known until sockeye hit the inlet next summer. For now, Fish and Game is sticking with the numbers Willette has crunched, numbers that show a below-average return for the summer of 2006.

Matt Tunseth is a freelance writer who lives in Kenai.

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