There’s no doubt that fishing causes changes to fish populations, which is why anglers dream of travelling to remote locations where few people have fished before. In some fisheries, larger individuals are selectively removed, which can result in a decrease in growth rate of individuals over time (since those who grow fastest get big, and then get caught). In other fisheries, aggressive and bold individuals may be more likely to be captured, resulting in the evolution of a more passive, shy population over time. These changes are referred to as ‘angling induced evolution’, and can have a very strong influence on fish behaviour.
However, two recent papers have suggested that different methods of fishing can select against individuals with different traits, and could cause different evolutionary outcomes for fish populations. In one of those studies, Dr. Alex Wilson and colleagues from Carleton University tested whether fish caught with hard-bodied ‘crank-bait’ type lures were behaviourally different than fish caught with soft plastic worms. First, they angled wild rock bass and large mouth bass using the different lures, and then brought the fish back to the lab for behavioral testing. They found that fish caught with crank-baits were generally bolder than fish caught with plastic worms, suggesting that the evolutionary consequences of angling might be dependent on the type of lure used!
Additional evidence that different fishing methods capture individuals with different behaviour came from a study by researchers at the University of Bergen (in Norway). The Norwegian team tested whether individuals captured by trawl fishing were behaviourally different than those captured with a passive minnow trap. They performed their study in the lab on guppies, using miniaturized trawls and traps to simulate a larger fishery. What they found was that bolder individuals were more likely to be caught by the trap than shy individuals, but were less likely to be caught by the trawl. The exact same individuals that were more likely to be caught by one method, were less likely to be caught by the other!
Taken together, the results provide some pretty strong evidence that different types of fishing capture fish with different personalities. As a result, it could be beneficial to have a diverse mix of angling activity (e.g. fly fishing, bait fishing, traps) in order to maintain behavioural diversity in a population. Furthermore, the results of these studies suggest that in areas with high fishing pressure it might be a good idea to try an unconventional tactic – if you do, you might just have evolution on your side!
ADM Wilson et al. 2015. Does angling technique selectively target fishes based on their behavioural type? Public Library of Science One. e0135848
Link to the paper here
B Diaz Pauli et al. 2015. Opposite selection on behavioural types by active and passive fishing gears in a a simulated guppy Poecilia reticulata fishery. Journal of Fish Biology 86:1030-1045.
Link to the paper here