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

Underwater caustics disrupt prey detection by a reef fish

Natural habitats contain dynamic elements, such as varying local illumination. Can such features mitigate the salience of organism movement? Dynamic illumination is particularly prevalent in coral reefs, where patterns known as 'water caustics' play chaotically in the shallows. In behavioural experiments with a wild-caught reef fish, the Picasso triggerfish (), we demonstrate that the presence of dynamic water caustics negatively affects the detection of moving prey items, as measured by attack latency, relative to static water caustic controls. Manipulating two further features of water caustics (sharpness and scale) implies that the masking effect should be most effective in shallow water: scenes with fine scale and sharp water caustics induce the longest attack latencies. Due to the direct impact upon foraging efficiency, we expect the presence of dynamic water caustics to influence decisions about habitat choice and foraging by wild prey and predators