THE EFFECT OF TURBIDITY ON GROUP SIZE DISTRIBUTION OF GOLDEN SHINER (NOTEMIGONUS CRYSOLEUCAS) FISH SCHOOLS

Abstract

Understanding how and why organisms form groups in nature is an essential aspect of collective animal behavior, but the influence of environmental conditions on group formation is an area of comparatively little exploration . This research seeks to determine the effect of turbidity, or the scattering of light by suspended particles in water, on the group size distribution of golden shiner fish (Notemigonus crysoleucas). The large tank experiments compared the group size distribution of 75 experimental fish in water of 0 NTU and 30 NTU over the course of two hours. It was found that a 30 NTU turbidity level increased the fragmentation of the fish, leading to a greater number of small, dispersed groups in 30 NTU water compared to 0 NTU water. For water of a 30 NTU turbidity level, the probability of an individual fish existing in a small or intermediate group increased, the median group size decreased, and the median group size expected for an individual decreased. The small tank experiments investigated whether this change in group size distribution observed in the large tank experiments was due to simply a decrease in the visual information available to the fish, or the presence of an additional behavioral response. Results suggest that raising water to a turbidity level of 30 NTU induced a repulsive behavioral response between groups of fish, and that this behavior was not present with fish in water at a 0 NTU and 15 NTU turbidity level. The probability of a fish avoiding the group increased as turbidity increased, as did the frequency of time that an individual fish spent avoiding a group. If turbidity does induce a repulsive effect between groups and individuals, then existing models used to predict group size distribution must quantify and incorporate this repulsion in conditions where the water is turbid. The impact of turbidity on group size distribution of fish schools will become an increasingly important area of research as climate change continues to increase the turbidity of earth’s surface water.