Turbidity increases risk perception but constrains collective behaviour during foraging by fish shoals

Abstract

Turbidity reduces the distance that animals can detect food, predators and conspecifics. How turbidity affects decision making in social contexts has rarely been investigated; moreover, it is unknown whether decreased shoaling in turbid water is due to visual constraints (a mechanistic explanation) or a reduced perception of predation risk (an adaptive explanation). Using a V-shaped decision making arena, we investigated the effect of turbidity on foraging in groups of threespined sticklebacks (Gasterosteus aculeatus). In turbid conditions, fish took longer to leave a refuge, longer to locate the food in one of the arms, and consumed less food once it was found. This increase in risk-averse behaviour was further supported by improved accuracy over repeated trials and a speed-accuracy trade-off only being observed in turbid conditions. Despite evidence of a higher perception of risk in turbid water, the fish to first choose an arm of the maze was more likely to be alone in turbid water, thus this individual lost the anti-predatory and decision making benefits of collective behaviour. This suggests that turbidity acts mechanistically as a visual constraint, shifting decisions away from being made collectively to being made by individuals separated from the group, which could have potential impacts for wild prey populations.

Negative effect of turbidity on prey capture for both visual and non‐visual aquatic predators

“…Thus, the detection of chemical cues from the presence of prey could stimulate predators to spend more time searching for prey, but this predator behavioural change may not imply in prey capture rates at similar or higher levels than those recorded to clear waters (Johannesen et al, 2012). Furthermore, behavioural studies have demonstrated that under high turbidity prey reduce their activity (Chamberlain & Ioannou, 2019;Kimbell & Morell, 2015) and can aggregate (Johannesen, Dunn, & Morrell, 2014;Ohata, Masuda, Takahashi, & Yamashita, 2014), which could result in reduced encounters between non-visual predators and their prey and decreased prey capture rate in turbid waters. For example, Ohata et al (2011) attributed the increase in survival of larval ayu Plecoglossus altivelis co-occurring with moon jellyfish Aurelia aurita (a tactile predator) in turbid waters to a decrease in swimming activity by ayu.…”

High turbidity levels alter coral reef fish movement in a foraging task

“…For species of planktivorous reef fish, turbidity can cause increased attack rates but decreased attack success 33 . Other behavioural effects of turbidity include changes to anti-predator behaviour 34 – 38 and predation rates 39 – 41 , reaction distance to visual stimuli 38 , 42 – 44 , response to sensory information e.g. 45 , foraging success 33 , 38 , 46 – 50 , and juvenile settlement and development 6 , 50 .…”

The impact of turbidity on foraging and risk taking in the invasive Nile tilapia (Oreochromis niloticus) and a threatened native cichlid (Oreochromis amphimelas)

“…Turbid environments also influence predator-prey interactions by changing the perception of risk in fish (Gregory 1993;Chamberlain and Ioannou 2019;Ehlman et al 2019). Prey may use turbid conditions as refugia from predators, where they are less likely to be detected (Engström-Öst et al 2009).…”