Data and R script for: Shoaling behaviour in response to turbidity in three-spined sticklebacks

Many fresh and coastal waters are becoming increasingly turbid because of
human activities, which may disrupt the visually-mediated behaviours of
aquatic organisms. Shoaling fish typically depend on vision to maintain
collective behaviour, which has a range of benefits including protection
from predators, enhanced foraging efficiency, and access to mates.
Previous studies of the effects of turbidity on shoaling behaviour have
focussed on changes to nearest neighbour distance and average group-level
behaviours. Here, we investigated whether and how experimental shoals of
three-spined sticklebacks (Gasterosteus aculeatus) in clear (<10
Nephelometric Turbidity Units (NTU)) and turbid (~35 NTU) conditions
differed in five local-level behaviours of individuals (nearest and
furthest neighbour distance, heading difference with nearest neighbour,
bearing angle to nearest neighbour, and swimming speed). These variables
are important for the emergent group-level properties of shoaling
behaviour. We found an indirect effect of turbidity on nearest-neighbour
distances driven by a reduction in swimming speed, and a direct effect of
turbidity which increased variability in furthest neighbour distances. In
contrast, the alignment and relative position of individuals was not
significantly altered in turbid compared to clear conditions. Overall, our
results suggest that the shoals were usually robust to adverse effects of
turbidity on collective behaviour, but group cohesion was occasionally
lost during periods of instability.