Shoal familiarity modulates effects of individual metabolism on vulnerability to capture by trawling.

J P W Hollins,D Thambithurai,S S Killen,B Koeck,D Bailey,T E Van Leeuwen,B Allan,Steven Cooke

doi:10.1093/conphys/coz043

J P W Hollins, D Thambithurai + Show 6 more

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https://doi.org/10.1093/conphys/coz043

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Abstract

Impacts of fisheries-induced evolution may extend beyond life history traits to more cryptic aspects of biology, such as behaviour and physiology. Understanding roles of physiological traits in determining individual susceptibility to capture in fishing gears and how these mechanisms change across contexts is essential to evaluate the capacity of commercial fisheries to elicit phenotypic change in exploited populations. Previous work has shown that metabolic traits related to anaerobic swimming may determine individual susceptibility to capture in trawls, with fish exhibiting higher anaerobic performance more likely to evade capture. However, high densities of fish aggregated ahead of a trawl net may exacerbate the role of social interactions in determining an individual fish's behaviour and likelihood of capture, yet the role of social environment in modulating relationships between individual physiological traits and vulnerability to capture in trawls remains unknown. By replicating the final moments of capture in a trawl using shoals of wild minnow (Phoxinus phoxinus), we investigated the role of individual metabolic traits in determining susceptibility to capture among shoals of both familiar and unfamiliar conspecifics. We expected that increased shoal cohesion and conformity of behaviour in shoals of familiar fish would lessen the role of individual metabolic traits in determining susceptibility to capture. However, the opposite pattern was observed, with individual fish exhibiting high anaerobic capacity less vulnerable to capture in the trawl net, but only when tested alongside familiar conspecifics. This pattern is likely due to stronger cohesion within familiar shoals, where maintaining a minimal distance from conspecifics, and thus staying ahead of the net, becomes limited by individual anaerobic swim performance. In contrast, lower shoal cohesion and synchronicity of behaviours within unfamiliar shoals may exacerbate the role of stochastic processes in determining susceptibility to capture, disrupting relationships between individual metabolic traits and vulnerability to capture.

Highlights

High mortality and selective removal of fish caused by fishing can induce changes in the phenotypic composition of fish stocks (Enberg et al, 2012; Heino et al, 2015)
Adjusted repeatability for individual time in the trawl net was significant (R = 0.303, 95% CI: 0.16–0.44 P < 0.001), as were unadjusted repeatabilities calculated within each treatment (R = 0.26, 95% CI:0.01–0.4, P = 0.004 and R = 0.23, 95% CI:0.06–0.45, P = 0.01, for familiar and unfamiliar shoals, respectively)
Repeatability of Ti calculated within each trial were comparatively low and similar between each treatment (R = 0.13, 95% CI: 0–0.33, P = 0.06 and R = 0.03, 95% CI: 0– 0.18, P = 0.4 for familiar and unfamiliar shoals, respectively)

Summary

Introduction

High mortality and selective removal of fish caused by fishing can induce changes in the phenotypic composition of fish stocks (Enberg et al, 2012; Heino et al, 2015). Physiological and behavioural traits have been shown to correlate with susceptibility to capture in laboratory and field studies (Redpath et al, 2010; Diaz Pauli et al, 2015; Killen et al, 2015a; Monk and Arlinghaus, 2017; Koeck et al, 2018). Active gears (including trawls and seine nets) pursue or encircle targeted fish with nets, and exploit fish behavioural responses, including shoaling, to elicit capture Physiological traits, such as individual swimming ability, may in this instance be linked to gear avoidance (Kim and Wardle, 2003; Killen et al, 2015a), which in turn may be related to traits determining individual aerobic and anaerobic metabolic capacity. The capacity to perform anaerobic metabolism may be important for evading capture from active gear types as it represents an individual’s ability to perform rapid bouts of burst swimming, often employed in escaping predators, or performing other high-speed manoeuvres (Marras et al, 2010)

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