Fish of the future may become less catchable

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Fishing over the years has got marine conservationists and researchers concerned about its possible impact on the stocks of these marine animals; however, it seems that fish may be learning a trick or two of their own to escape the nets.

Researchers have revealed through a new research that fish that have managed to evade the nets of trawlers the first time around are evolving and maybe learning tricks needed to escape from them all the time. Researchers say that fish are learning to swim faster to evade the nets and this particular adaptation may be a natural evolution from a prey trying to get away from the predator.

Scientists at the University of Glasgow investigated in their study to check whether commercial trawling has a similar effect on fish and whether this drives evolutionary change in them to evading capture. Researchers speculate that over time not only will the fish be less catchable, but the evolution could lead to physiological changes in future fish populations.

Dr Shaun Killen of the Institute of Biodiversity, Animal Health and Comparative Medicine, said: “There is a lot of concern on how overfishing is affecting the abundance of wild fish, consequences for the economy, employment and the ecosystem as a whole.”

Killen said that in midst of all these issues, scientists have been ignoring one particular aspect – the evolutionary changes that may be induced to remaining the fish that that survived the nets.

Researchers set up an experiment involving simulated trawling with schools of wild minnows to investigate two key questions around fisheries-induced evolution – whether some individuals within a fish shoal were consistently more susceptible to capture by trawling than others, and if so, was susceptibility related to individual differences in swimming performance and metabolism?

The experiment was carried out on 43 individual fish and researchers measured their swimming ability, metabolic rate, and indicators of aerobic and anaerobic physical fitness. They then placed them in a tank with a trawling net in a simulation that was repeated several times, enabling the identification of individuals which were more susceptible to capture.

Researchers observed that fish will swim at a steady pace ahead of the nets for as long as possible, but a few will eventually tire and fall back and get captured.

Researchers found that some fish were more susceptible to capture than others and this was strongly related to anaerobic capacity – the ability to engage in short periods of intense physical activity which demands more oxygen than is available from breathing alone.

Maximum aerobic swim speed was also negatively correlated with vulnerability to trawling. Metabolic rate – an indicator of how much energy an animal needs to live – was highest among fish that were least vulnerable to trawling but this relationship probably arose through correlations with anaerobic capacity.

“Using simulated trawling, our study provides the first evidence 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 makeup of descendant populations that avoid fisheries capture”, researchers said.

The researchers now want to study fish in the wild to see if they get the same results. The findings of the study have been published in the journal Proceedings of the Royal Society B.