December 4, 2012 report
Researchers find fishing tends to lessen population of best male bass
With largemouth bass, after the female lays her eggs, it's up to the male to protect them. They do so by fanning the eggs and driving away threats. Those that do a better job of it, tend to have more offspring survive. But, this new researcher suggests, the same aggressive behavior that some bass exhibit when protecting their young, can cause them to be more vulnerable to being caught by sport fishermen.
Because of the popularity of bass fishing, the fish are bred in reservoirs and are then released into the wild in places where fishermen go to catch them; otherwise all the fish would be caught and there would be none left to fish. Over time those that manage fish populations have come to realize that some bass are more likely to strike at a lure and thus be caught then others. Some fishermen prefer such fish, while others prefer those that are more difficult to catch. To serve the needs of both, both types of fish have been bred and are then released into different areas to account for the different tastes.
Suspecting that the two groups of fish might have other differences as well, the research team set up underwater cameras to watch the males as they cared for the eggs of their young in hatcheries. In so doing, they discovered that those fish that took their job very seriously, appeared to consider a lure a threat, and thus were more likely to attack it, resulting in them being caught. Conversely, those fish that were more lackadaisical in their responsibilities tended to be less likely to be caught.
The end result, the researchers say, is that the best fathers wind up being the ones that get caught, thus their young never hatch and grow up to pass on their good father genes, which means that recreational fishing actually impacts the evolution of bass populations.
Fisheries-induced evolution and its impact on the productivity of exploited fish stocks remains a highly contested research topic in applied fish evolution and fisheries science. Although many quantitative models assume that larger, more fecund fish are preferentially removed by fishing, there is no empirical evidence describing the relationship between vulnerability to capture and individual reproductive fitness in the wild. Using males from two lines of largemouth bass (Micropterus salmoides) selectively bred over three generations for either high (HV) or low (LV) vulnerability to angling as a model system, we show that the trait "vulnerability to angling" positively correlates with aggression, intensity of parental care, and reproductive fitness. The difference in reproductive fitness between HV and LV fish was particularly evident among larger males, which are also the preferred mating partners of females. Our study constitutes experimental evidence that recreational angling selectively captures individuals with the highest potential for reproductive fitness. Our study further suggests that selective removal of the fittest individuals likely occurs in many fisheries that target species engaged in parental care. As a result, depending on the ecological context, angling-induced selection may have negative consequences for recruitment within wild populations of largemouth bass and possibly other exploited species in which behavioral patterns that determine fitness, such as aggression or parental care, also affect their vulnerability to fishing gear.
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