Is Overfishing Changing the Gene Pool?

The findings challenge the long-held belief that if a few million fish are left, even after overfishing, that will be enough for a species to replenish itself. In a separate study three years ago, researchers at the University of Washington were surprised when they studied a population of New Zealand snapper that had been fished down to about 3 million.

That should have allowed for recovery, but the researchers found that only one in 10,000 fish was capable of breeding, so the genetic diversity of the population depended on as little as a few hundred fish.

Reduced diversity leaves the species more susceptible to toxins, and less likely to survive much less rebound.

So it would seem that longer periods of reduced or banned fishing would be required for overfished stocks to be rehabilitated.

But the Stony Brook researchers themselves point out that what happens in the lab is not directly parallel to what happens in the real world. Most commercial fish species live much longer than a year, and have overlapping generations, so "similar responses in wild fisheries are unlikely to be as rapid," they report.

Still, there is that anecdotal evidence that is hard to ignore. My home is in the heart of Alaska's king salmon runs, and each fall the cultural event of the year takes place. The Great Northern Salmon Derby pits fisher against fisher, friend against friend, husband against wife, in the annual effort to land the biggest king salmon.

Just a few years ago, that required a fish that would weigh in at between 40 and 50 pounds, and sometimes even more.

In recent years, however, the winner has weighed a relatively puny 30 to 35 pounds.

Of course, many factors may figure in to that. But ask any fisher around here and he, or she, will tell you the fish are smaller now.

And if the findings at Stony Brook apply to the real world, that may be because the big fish are harvested before they reach the spawning grounds, and thus their genes are lost. So it may be many, many generations before the big kings return, if indeed they ever do.

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