Fish 'evolving to avoid trawler nets' by swimming faster

fishing net Image copyright Getty Images

Fish may be evolving to swim faster so they can avoid capture in trawler nets, according to research.

Scientists at the University of Glasgow found that fitter fish are better at evading nets.

They said that, over time, it could lead to physiological changes in fish.

Study leader Dr Shaun Killen: "Intense fishing pressure may cause evolutionary changes to the remaining fish that are not captured."

The university group used simulated trawling with schools of wild minnows to investigate whether some individual fish were consistently more susceptible to capture.

They measured the swimming ability, metabolic rate and indicators of aerobic and anaerobic physical fitness of 43 fish.

The minnows were then placed in a tank with a simulated trawling net to identify those most susceptible to capture.

'Selective harvest'

Dr Killen, of the Institute of Biodiversity, Animal Health and Comparative Medicine, said: "Fish being trawled will try to swim at a steady pace ahead of the mouth of the net for as long as possible, but a proportion will eventually tire and fall back into the net.

"Fish that escape trawling are those that can propel themselves ahead of the net or move around the outside of the net. The key question is whether those that escape are somehow physiologically or behaviourally different to those that are captured.

"Most trawlers travel at the about same speed as the upper limit of the swim speed of the species they are targeting.

"While trawling nets can be in the water anywhere between 10 minutes to several hours, whether or not fish enter the net is generally decided within a few minutes of when they end up at the trawl mouth."

The study is published in the journal Proceedings of the Royal Society B and the researchers want to carry out a similar study on fish in the wild.

Dr Killen said available evidence suggested selective harvest can lead to genetic change within wild populations for specific traits.

She added: "Using simulated trawling, our study provides the first evidence that better-swimming fish, and those with higher metabolic rates, are more likely to escape capture.

"Over time, the selective removal of poor-swimming fish could alter the fundamental physiological make-up of descendant populations that avoid fisheries capture."

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