Evolutionary effects of fishing gear on foraging behavior and life‐history traits

Abstract

Fishing gears are designed to exploit the natural behaviors of fish, and the concern that fishing may cause evolution of behavioral traits has been receiving increasing attention. The first intuitive expectation is that fishing causes evolution toward reduced boldness because it selectively removes actively foraging individuals due to their higher encounter rate and vulnerability to typical gear. However, life‐history theory predicts that fishing, through shortened life span, favors accelerated life histories, potentially leading to increased foraging and its frequent correlate, boldness. Additionally, individuals with accelerated life histories mature younger and at a smaller size and therefore spend more of their life at a smaller size where mortality is higher. This life‐history evolution may prohibit increases in risk‐taking behavior and boldness, thus selecting for reduced risk‐taking and boldness. Here, we aim to clarify which of these three selective patterns ends up being dominant. We study how behavior‐selective fishing affects the optimal behavioral and life‐history traits using a state‐dependent dynamic programming model. Different gear types were modeled as being selective for foraging or hiding/resting individuals along a continuous axis, including unselective fishing. Compared with unselective harvesting, gears targeting hiding/resting individuals led toward evolution of increased foraging rates and elevated natural mortality rate, while targeting foraging individuals led to evolution of decreased foraging rates and lower natural mortality rate. Interestingly, changes were predicted for traits difficult to observe in the wild (natural mortality and behavior) whereas the more regularly observed traits (length‐at‐age, age at maturity, and reproductive investment) showed only little sensitivity to the behavioral selectivity.

Hormones as adaptive control systems in juvenile fish

“…From a life history perspective one would expect a decrease in length growth as the individual gets larger, due to fewer potential predators for larger fish (Bystrom et al, 2015; Persson et al, 1996) and how the increased survival prospects lead to slower optimal growth that put more weight on survival and the future. However, larger fish are more efficient feeders because they are less exposes to risk when they are foraging (Claireaux et al, 2018), countering the first effect. These two opposing forces explain the rather linear growth seen in the predicted juvenile growth from this model, an observation also seen in other adaptive models for the ontogeny of growth when acquisition is flexible (Claireaux et al, 2018; Jørgensen and Holt, 2013).…”

“…However, larger fish are more efficient feeders because they are less exposes to risk when they are foraging (Claireaux et al, 2018), countering the first effect. These two opposing forces explain the rather linear growth seen in the predicted juvenile growth from this model, an observation also seen in other adaptive models for the ontogeny of growth when acquisition is flexible (Claireaux et al, 2018; Jørgensen and Holt, 2013).…”

Harvesting-induced evolution of collective risk-taking behavior and changes to the circadian system in a fish

“…The evolution of a fast life history is reinforced by harvesting mortality being size-selective (6). Life history evolution can alter correlated traits, such as physiological and behavioral traits (6-9). However, physiological and behavioral adaptations in response to harvesting are much less understood compared to harvesting-induced changes to life-histories (2, 8).…”

“…For example, the pace-of-life syndrome proposes that life-history traits, such as growth rate or maturation size, are systematically and genetically related to behavioural and physiological traits (11). Accordingly, life-history adaptations caused by fisheries can also be expected to indirectly affect the physiology and behavior of exploited fishes (5, 6, 9). Secondly, fisheries can also directly select on physiological and behavioural traits, e.g., because bold, aggressive, social or stress-resilient fishes are preferentially harvested with certain gears (12-16).…”

Evolutionary impact of size-selective harvesting on shoaling behavior: Individual-level mechanisms and possible consequences for natural and fishing mortality

“…Large size-selective harvesting, where larger fish have a higher mortality risk than smaller ones, is a typical selectivity pattern in fisheries that has been shown to decrease individual boldness (3), and may in turn also affect collective phenotypes, such as shoaling. Adaptive changes in individual fish boldness can emerge through at least three mechanisms (3,9,25). First, life histories and individual behavioral traits are often correlated following the pace of life (26).…”