Shoal size as a key determinant of vulnerability to capture under a simulated fishery scenario

Abstract

Group living is widespread among animals and has a range of positive effects on individual foraging and predator avoidance. For fishes, capture by humans constitutes a major source of mortality, and the ecological effects of group living could carry‐over to harvest scenarios if fish are more likely to interact with fishing gears when in social groups. Furthermore, individual metabolic rate can affect both foraging requirements and social behaviors, and could, therefore, have an additional influence on which fish are most vulnerable to capture by fishing. Here, we studied whether social environment (i.e., social group size) and metabolic rate exert independent or interactive effects on the vulnerability of wild zebrafish (Danio rerio) to capture by a baited passive trap gear. Using video analysis, we observed the tendency for individual fish to enter a deployed trap when in different shoal sizes. Fish in larger groups were more vulnerable to capture than fish tested individually or at smaller group sizes. Specifically, focal fish in larger groups entered traps sooner, spent more total time within the trap, and were more likely to re‐enter the trap after an escape. Contrary to expectations, there was evidence that fish with a higher SMR took longer to enter traps, possibly due to a reduced tendency to follow groupmates or attraction to conspecifics already within the trap. Overall, however, social influences appeared to largely overwhelm any link between vulnerability and metabolic rate. The results suggest that group behavior, which in a natural predation setting is beneficial for avoiding predators, could be maladaptive under a trap harvest scenario and be an important mediator of which traits are under harvest associated selection.

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

“…Evidence of synchronisation in behaviour around the trawl net was present in both familiar and unfamiliar shoals, suggesting that individuals within shoals are likely using a form of information transfer among individuals to avoid capture, as has been observed in previous experiments using trawl simulations (Brown and Warburton, 1999) and novel-avoidance tasks (Brown and Laland, 2002). This result supports the notion that while active gears have the capacity to selectively remove the slowest swimming fish, and drive phenotypic change in exploited fish stocks, extrinsic social factors may play a role in modulating this effect (Hollins et al , 2018; Thambithurai et al , 2018).…”

“…Conformity of behaviour within a fish shoal can occur where members respond to stimuli, and these responses subsequently propagate through the shoal, manifesting as a collective behaviour (Brown and Laland, 2002; Magnhagen and Staffan, 2004; Marras et al , 2011). While behavioural conformity may enable groups of fish to efficiently exploit escape routes in pursuing gears (Brown and Warburton, 1999) through a ‘follow the leader’ type principle, there is also evidence that it may increase susceptibility to capture of shoaling fish when the collective decision of a shoal is to voluntarily enter fishing gear, as opposed to escaping it (Rose, 1995; Thambithurai et al , 2018). Trawls often exploit this behaviour to increase capture efficiency (Ryer, 2008) with gear components specifically designed to concentrate pursued fish ahead of a trawl mouth in a behaviour known as herding (Ryer et al , 2009).…”

Experimental Size‐Selective Harvesting Affects Behavioral Types of a Social Fish

“…; Thambithurai et al. ). We predicted that the large‐ and small‐harvested females would evolve higher and lower sociability than control females, respectively.…”

“…; Monk and Arlinghaus ; Thambithurai et al. ). Moreover, there are only a few theoretical studies focused on the effects of selective harvesting on the evolution of fish personality, and these studies have largely focused on boldness as the focal trait under selection (Andersen et al.…”

Social dynamics obscure the effect of temperature on air breathing in Corydoras catfish

“…Water was mixed throughout the respirometry system using a peristaltic pump attached to a timer. Respirometry chambers were flushed with oxygenated water for 2 min every 8 min, and then switched off, sealing the respirometers to measure the rate of oxygen uptake of each fish ( Hollins et al, 2019 ; Thambithurai et al, 2018 ). Fish were kept in their chambers overnight for a total of 16 h to allow for estimation of SMR.…”