Every angler knows that some fish are easier to catch than others. For some reason, certain fish find lures, bait and flies irresistible, while other fish timidly lurk in deep pools and frustrate even the most persistent angler. In catch and keep fisheries, fish that are more likely to be caught are removed from the gene pool and this process can lead to what is called ‘angling induced evolution’. Over time, the characteristics that cause fish to be easily caught are eliminated from the population, and the characteristics that cause fish to avoid being caught become more common.
In a study in 2011, researchers from the Illinois Natural History Survey and Carleton University tested how angling induced evolution changes the foraging behavior of largemouth bass. Using a small pond in which all largemouth bass were marked, the scientists tracked how many times each fish was captured in a given year. If a fish was captured more than 4 times in a year it was allowed to breed to produce a ‘high angling vulnerability’ line of offspring, while fish that were never captured were bred to produce a ‘low vulnerability’ line. The researchers repeated this process over 4 generations to cause evolutionary changes.
After the angling induced evolution was completed, the researchers quantified the foraging behavior of juvenile fish in tanks with small bluegill sunfish. They found that fish selected for low angling vulnerability had higher prey rejection rates and would only attack prey if it was close to them, which is consistent with the behavior of fish that are hard to catch. Interestingly though, the low vulnerability fish actually caught more prey overall than did the high vulnerability fish, and they were more efficient at converting food into growth.
The authors concluded that angling induced evolution can cause important changes in foraging behavior in relatively short time periods. If they can observe changes in only 4 generations, we can imagine the changes that thousands of years of fishing has caused on natural fish populations!
Citation: M Nannini et al. 2011. The influence of selection for vulnerability to angling on foraging ecology in largemouth bass Micropterus salmoides. Journal of Fish Biology 79: 1017-1028.
Find the paper here