Unbridled fishing pressure can drive species to the brink of extinction, but can commercial fishing drive evolution?

The drive to reproduce and avoid predation are the two main drivers of evolutionary adaptation. Arms races between predator and prey can produce dramatic evolutionary change.

Researchers at Glasgow University wanted to know whether commercial fishing trawlers could influence evolution in the same way the ocean's hunters do.

Specifically, scientists set out to find out if some fish were more susceptible to being captured by trawlers than others, and if so, would that susceptibility correlate with swimming performance and metabolism?

To determine as much, researchers put a school of 43 fish in tanks and measured each fish's swimming ability, metabolic rate and other aerobic and anaerobic fitness factors. Then, the researchers subjected the captive fish to a trawling simulation.

"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," Shaun Killen, a biologist at Glasgow, explained in a press release.

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

The results of Killen's experiments showed that some fish are indeed more susceptible to capture, while fitter, better-swimming fish were more likely to escape.

"Humans are effective predators, and selective harvest of animals by humans probably represents one of the strongest drivers of evolutionary change for wild animal populations," said Killen. "Hunting and fishing are selective processes which often remove individuals that, under normal circumstances, may have the highest reproductive potential. Available evidence suggests selective harvest can lead to genetic change within wild populations for specific traits."

Killen says his work, published in the journal Proceeding B, is proof that these changes are likely already happening.

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