Fish are evolving to outsmart fishermen

You might not be able to tell from the amount of sushi bars around Vancouver, but the world’s fisheries are in danger. More than 85 per cent of them are pushed beyond their biological limit to replenish fish stock and it’s only getting worse.

Measures to curb this trend include establishing “no-take” marine reserves that provide a safe haven for fish. However, their effectiveness has been under scrutiny.

“There’s actually been a push-back from the tuna fisheries in general saying fish like tuna and sharks — because they swim a lot and move around a lot — will just swim out of the reserves,” said Jonathan Mee, a UBC alumnus and lead author of a new study focusing on the effectiveness of marine reserves. “That motivated us to do this model suggesting, ‘well, maybe you’re not accounting for the possibility of evolution.’”

The research, in collaboration with UBC’s Biodiversity Research Centre and the Sea Around US project at the Institute for the Oceans and Fisheries, used mathematical simulations to model the behaviour of tuna and shark species to investigate the effectiveness of marine reserves.

Based on their simulation, researchers say fish in marine reserves can evolve and adapt their behaviors in response to fishing pressures to avoid the nets.

“If things die when they swim out of the reserve, that’s really strong natural selection,” said Mee, a faculty member of Mount Royal University who conducted much of the work at UBC as part of his postdoctoral fellowship. “A lot of death equals very effective selection.”

The model was built using real-world data collected on species of tuna and sharks. Individuals were then assigned variants of a gene for movement distance. Some had a variant for large movement distances, while some for small movement distances. The frequency of these genes can then be tracked to model evolution.

The relationship between movement rate and genetics in tuna and shark is not well-understood, however. “It would be weird if the amount they moved didn’t have some genetic basis,” said Mee.

Studies on other species of fish do point to heritability of movement rate.

The results are optimistic and support the efficacy of marine reserves for protecting biodiversity within them. The effects of fishery-induced evolution on tuna and sharks to stay within the reserves were strong, with evidence supporting significant movement pattern changes in under 50 years.

However, this comes as no surprise. “Anyone who studies evolution explicitly is quite aware that evolution can happen quite rapidly,” said Mee. “Our goal was to publish the idea of rapid evolution in the context of conservation and fisheries.”

One thing that did surprise researchers was how an important mechanism for the conservation of one species may not be effective in conserving another.

“We wanted to explore some of the differences between different species of tuna and different species of sharks. It’s not going to protect everything.”