Aqua: Fish becoming small and meek

Fishing may result in a 'contemporary evolution' where large, fertile males are removed, leaving populations of smaller fish struggling.

Commercial fishing results in direct selection against bold, fast-growing fish, potentially affecting the ability of harvested populations to recover, according to a new study by fish scientists in Australia and Canada.

The scientists, who simulated an intensive gillnet fishery in two rainbow trout-stocked experimental lakes in Canada, found that regulations governing the size of fish caught are not sufficient to prevent human-driven "contemporary evolution".

Dr Peter Biro from the University of Technology, Sydney and Professor John R. Post of the University of Calgary, said the survivors of commercial harvesting tended to be more meek, less active and less fecund.

"Fish with bold personalities are more active in finding food and grow fast, but are quickly removed by commercial fishing," Dr Biro said. "They are more vulnerable because they swim around more and are less likely to shy away from fishing gear.

"Given the link between personality and growth, we've found that genotypes with bold personality are removed at three times the rate of shy genotypes, leaving behind mainly slow-growing fish.

"What this data shows us is that even if we introduce fishing regulations like minimum size limits, fishing will continue to remove bolder individuals.

"And, because fast-growing fish are typically larger at age and more fecund (more eggs), the loss of these genotypes may potentially hinder the recovery of exploited fish populations and lower the fishable biomass and yield."

Dr Biro said the results should apply to many fish populations and fishing methods other than gillnets.

"In fact the use of high-tech fish locating devices may well target fast-growing fish to a greater extent than our data would suggest, as faster-growing individuals tend to congregate in food-rich but risky habitats and we specifically did not target these areas," he said.

"What our study highlights is the importance of adopting behavioural and evolutionary ecology perspectives to our understanding of the short and long-term effects of fish harvest and the need to foster collaboration between fishery scientists and evolutionary ecologists."

The results of the research have been published in the USA-based scientific journal Proceedings of the National Academy of Sciences.

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Aqua: Fish becoming small and meek