Dynamic visual noise promotes social attraction, but does not affect group size preference, in a shoaling fish

Gathering information from the environment allows animals to make informed behavioural decisions, with individuals sampling information either privately or via social cues from group members. Environmental noise, however, may disrupt the ability of animals to gather information in their environment. Therefore, social interactions could be disrupted by environmental noise, or adapted to mitigate the costs associated with compromised perception in noisy environments. Here we tested whether the presence of water caustics, a natural form of visual noise prevalent within shallow aquatic habitats, affects the social decisions of shoaling fish. In a classic experimental paradigm, individual three-spined sticklebacks, Gasterosteus aculeatus, were given a choice between two conspecific shoals differing in size while immersed in different levels of visual noise. Fish showed greater social attraction towards conspecifics as noise levels increased, measured by a reduction in the distance they maintained from others. While sticklebacks only showed clear preferences for groups that had at least four more members than another group, there was no evidence that visual noise level influenced fish’s preference to associate with these larger shoals, nor did it change the preferences for other shoal sizes. Our findings suggest that, at the group sizes tested, visual noise increases individual stickleback’s social attraction towards conspecifics, but does not affect their decision to associate with the larger of two groups. Such changes to social behaviour may reflect the consequences of having a reduced ability to sample private, but not social, information in noisy environments.This work was supported by the Whitten Program in Marine Biology and a Swedish Research Council (grant number 2018-04076), and an ISSF Wellcome Trust Gran

Spatial clustering of trumpetfish shadowing behaviour in the Caribbean Sea revealed by citizen science

AbstractThe West Atlantic trumpetfish (Aulostomus maculatus) performs an unusual hunting strategy, termed shadowing, whereby a trumpetfish swims closely behind or next to another ‘host’ species to facilitate the capture of prey. Despite trumpetfish being observed throughout the Caribbean, observations of this behaviour appear to be concentrated to a handful of localities. Here we assess the degree of geographical clustering of shadowing behaviour throughout the Caribbean Sea, and identify ecological features associated with the likelihood of its occurrence. To do this, we used a citizen science approach by creating and distributing an online survey to target frequent divers across this region. While the vast majority of participants observed trumpetfish on nearly every dive across the Caribbean, using random labelling spatial analyses, we found the frequency of shadowing behaviour was geographically clustered; participants that were within ~ 120 km of each other reported observations of shadowing that were more similar than would be expected by chance. Our survey also highlighted that trumpetfish were more likely to be observed shadowing than observed alone in a particular habitat type, and with particular host species, suggesting potential ecological factors that could drive the uneven distribution of this behaviour. Our results demonstrate that this behavioural hunting strategy is spatially clustered and, more generally, highlight the power of using citizen science to investigate variation in animal behaviour over thousands of square kilometres.</jats:p