A new research conducted in the United Kingdom raises the possibility that fish are becoming more and more adept at evading capture through conventional fish catching techniques such as trawling.

Researchers at the University of Glasgow, led by Dr. Shaun Killen, discovered that pressure from intensive fishing could potentially lead to evolutionary changes to those fish that are not captured by the fishermen.

In a study featured in the journal Proceedings of the Royal Society B, Killen and his colleagues made use of trawling techniques to capture schools of fish known as wild minnows in order to identify if some individual fish were consistently more vulnerable to capture than others.

They examined several factors during the experiment such as the swimming ability of the fish and their metabolic rates, as well as anaerobic and aerobic indicators that would allow the scientists to determine the fitness of 43 of the animals.

The wild minnows were then transferred to a fish tank with a simulated trawling net to find out those fish that are more susceptible to this fishing method.

Killen explained that while some of the fish being trawled by the net will try to swim at a consistent pace to evade capture, many of them will eventually begin to tire and fall back.

Those animals that are able to avoid capture are the ones that can swim hard enough to pace ahead of the trawling net or at least maneuver themselves outside of its range.

Killen said that the important question to answer is whether or not the fish that successfully evade the net are somehow behaviorally or physiologically different compared to those that are captured by it.

He added that most trawling ships travel at the same speed as the maximum speed of the species of fish they are trying to catch.

Some of the trawling nets that these ships place in the water can stay there from 10 minutes up to several hours, but the actual catching the fish only takes about a few minutes especially once the animals end up at the mouth of the trawl.

The findings of the study show that genetic changes in specific traits within wild fish populations can be made through selective harvest.

Killen pointed out that fish that are better swimmers, and those that have faster metabolic rates, have a better chance of evading capture by the trawling net.

He said that over time, the removal of poor-swimming fish through natural selection could led to key physiological changes in descendant populations, allowing them to become more adept at avoiding capture.

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