60-Second Science

Nets Drive Evolution of Small Fish

In a test lake stocked with two types of trout, fishing with nets mostly caught larger, faster-growing fish, leaving smaller, slower growers to survive and pass on those traits. Karen Hopkin reports.

Being a big fish in a small pond is more likely to get you noticed. That’s good news if you’re, say, the best pitcher in your little league division. But it’s not so good if you’re an actual fish. Because bigger fish are the ones that tend to get caught. Not only is that bad news for the fish, but it may be bad for the whole fish population. Or so say scientists from Australia and Canada in the online edition of the Proceedings of the National Academy of Sciences. They find that fishing for the largest individuals targets the fastest growers, leaving behind their slower-growing counterparts. Which means that current fishing practices may favor the evolution of slower-growing fish.
The scientists stocked two small lakes in British Columbia with two strains of rainbow trout: one that grows quickly and is more aggressive in chasing down food and another that grows slowly and tends to be more cautious. They then used commercial gillnets to fish the lakes and found that they bagged the bolder fish three times faster than the shy ones, which were left behind to multiply. So we could inadvertently be breeding fearful small fry that are nearly impossible to catch. Which would make them…hard-to-see food.

—Karen Hopkin

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