The battle between harvest and natural selection creates small and shy fish

Abstract

Harvest of fish and wildlife, both commercial and recreational, is a selective force that can induce evolutionary changes to life history and behavior. Naturally selective forces may create countering selection pressures. Assessing natural fitness represents a considerable challenge in broadcast spawners. Thus, our understanding about the relative strength of natural and fisheries selection is slim. In the field, we compared the strength and shape of harvest selection to natural selection on body size over four years and behavior over one year in a natural population of a freshwater top predator, the northern pike (Esox lucius). Natural selection was approximated by relative reproductive success via parent–offspring genetic assignments over four years. Harvest selection was measured by comparing individuals susceptible to recreational angling with individuals never captured by this gear type. Individual behavior was measured by high-resolution acoustic telemetry. Harvest and natural size selection operated with equal strength but opposing directions, and harvest size selection was consistently negative in all study years. Harvest selection also had a substantial behavioral component independent of body length, while natural behavioral selection was not documented, suggesting the potential for directional harvest selection favoring inactive, timid fish. Simulations of the outcomes of different fishing regulations showed that traditional minimum size-based harvest limits are unlikely to counteract harvest selection without being completely restrictive. Our study suggests harvest selection may be inevitable and recreational fisheries may thus favor small, inactive, shy, and difficult-to-capture fish. Increasing fractions of shy fish in angling-exploited stocks would have consequences for stock assessment and all fisheries operating with hook and line.

Social associations in common carp (Cyprinus carpio): Insights from induced feeding aggregations for targeted management strategies

“…Individual behavior of fish can be influenced by others and in response to management efforts, leading to a nonrandom or uneven distribution of behavior types. For example, Monk et al ( 2021 ) found that sustained angling pressure on northern pike Esox lucius resulted in “small, inactive, shy, and difficult‐to‐capture fish,” not purely by natural selection suggesting that removal strategies impact fish populations (such as through behavior and growth). The resulting harder‐to‐catch fish and likely diminished management success suggest the superfeeders could be important and warrant more study.…”

Size-selective mortality fosters evolutionary changes in collective learning across ontogeny and decision-making in zebrafish,Danio rerio

“…Size-selective harvesting fosters evolutionary changes in boldness as demonstrated through a range of theoretical (Andersen et al 2018, Arlinghaus et al 2017, Claireaux et al 2018) and empirical (Medaka Oryzias latipes : Diaz Pauli et al 2019, zebrafish: Roy et al 2021a, Sbragaglia et al 2020) investigations. Specifically, positive size-selection tends to favour evolution of shy fishes as demonstrated in theoretical (Andersen et al 2018, Claireaux et al 2018) as well as empirical studies (Diaz Pauli et al 2019, Monk et al 2021). Therefore, it is possible that the cognitive abilities of fish are evolutionarily shifted towards slower learning and reduced memory ability in response to positive size-selection.…”

Contrasting structural complexity differentiate hunting strategy in an ambush apex predator

“…Our results suggest that higher activity levels and thus energy expenditure can be associated with higher growth, which must be balanced by increased consumption. On the other hand, piscivorous fish in habitats with low structural complexity may be more vulnerable to fishing mortality, since the increased activity implies increased encounter probabilities with anglers and/or fishing nets 92 . Ecosystem effects of observed behavioural differences are beyond the scope of this paper and further research is strongly required in this respect, but we argue that the design of concurrently comparing lakes with contrasting structural complexity has a large potential for such research.…”