Commercial and recreational fishing may be doing more than just reducing fish populations—it could be reshaping the very evolution of fish species. As global fisheries remove an estimated 1.6 trillion wild fish annually, emerging research suggests that the traits making certain fish more susceptible to capture may also be heritable, leading to generational shifts in behavior, growth patterns, and even cognitive ability.
Not all fish respond the same when confronted by anglers. In freshwater environments, such as lakes populated by pike, some individuals remain elusive, while bolder counterparts are more likely to take bait. These more aggressive fish are frequently the first to be caught, leaving their cautious peers to reproduce. Over time, this dynamic could shift the behavioral traits of entire populations.
Historically, fishing’s impact was viewed largely through the lens of abundance. However, recent scientific studies reveal a subtler, long-term influence: selective harvesting often targets large, bold, or aggressive individuals, unintentionally shaping the future gene pool. According to evolutionary physiologist Amélie Crespel of the University of Turku in Finland, this could impact food webs on a broader scale, potentially altering aquatic ecosystems.
The size-selective nature of industrial fishing methods like trawling has already prompted concern. Species such as Atlantic cod have become smaller in recent decades, in part due to large, older fish being systematically removed from populations. Evolutionary biologist Beatriz Pauli of the Norwegian Directorate of Fisheries suggests this is more than coincidence. Populations exposed to intense harvesting pressures may evolve to grow smaller and mature faster in order to reproduce before being caught.
Supporting this theory, Pauli’s research at the University of Bergen simulated trawl fishing on guppies. In tanks where larger fish were consistently removed, males matured faster and females began producing offspring at younger ages. These fish also exhibited behavioral changes—acting bolder and eating more to support rapid growth. While not definitive genetic proof, the findings strongly suggest evolutionary adaptation under fishing pressure.
Behavior-based methods like angling, gill-netting, and trapping seem to accelerate these effects. Robert Arlinghaus of the Leibniz Institute of Freshwater Ecology and Inland Fisheries documented that bold, active pike in a German lake were more likely to be caught, gradually shifting the population toward shyness. Given that personality traits in fish are partly genetic, a long-term change in behavioral composition could be underway.
Further experiments revealed similar patterns in largemouth bass in Illinois. The most aggressive males—those most likely to strike artificial lures—also turned out to be the most attentive parents. Unfortunately, these same traits make them prime targets for anglers, potentially reducing the number of high-quality nest guardians in future generations.
Social behavior may also be evolving under human pressure. Studies on zebrafish by Shaun Killen of the University of Glasgow found that highly social individuals are more likely to be caught in traps. Once one fish enters, others often follow—even returning after escaping if peers remain inside. This herd-following behavior could lead to evolution against sociality, which could further alter survival strategies in the wild.
Cognitive evolution may also be in flux. If fish are forced to mature quickly to ensure reproduction, less energy may be allocated to brain development. This could lead to declines in overall intelligence. However, there may be exceptions in recreational fisheries where catch-and-release is common. In such environments, fish that learn to avoid hooks have a better chance of surviving and reproducing—potentially leading to smarter, more elusive fish in the long run.
The long-term consequences of these changes are still unclear, but the impact on fisheries is already apparent. As bolder, larger fish are harvested, remaining populations may be composed of smaller, less catchable individuals. This could reduce yield, lower profits, and increase effort required to catch the same quantity of fish.
If these traits are genetically ingrained, reversing the changes could be difficult. Recovery may be quicker if shyness or small size is temporary, but if fishing has already altered the gene pool, populations may take decades to rebound. Crespel warns that these evolutionary shifts compound existing stressors like climate change and pollution, further destabilizing aquatic ecosystems.
Trophic dynamics could also shift. Smaller, fast-living fish may overconsume their prey, or less-social fish might lose protective benefits of schooling, making them more vulnerable. On the flip side, more timid predatory fish might eat less, allowing prey populations—especially herbivores—to increase, possibly leading to overgrazing of underwater vegetation.
To mitigate these unintended outcomes, scientists suggest that fisheries reconsider how fish are targeted. Strategies that reduce emphasis on specific traits—like size or boldness—and that avoid overharvesting could help preserve natural diversity and stabilize fish populations for the long term.
In the words of Crespel: “It’s time to start considering how to avoid steering the evolution of fish in unnatural directions.”
Image/Source: nautil
