Meeting Abstract
Many fish live in habitats with flowing water and are subject to predation in such environments. However, there are few data to indicate how water flow affects fish escape performance. To test for effects of water flow on fish escapes, we measured the fast-start performance of juveniles of the amphidromous Hawaiian goby, Sicyopterus stimpsoni. In nature, these fish must escape ambush predation while migrating to upstream adult habitats, through high-velocity flow. We used a variable-speed flow tank to establish three different flow conditions encountered in natural streams (zero, low, and high flow). With fish oriented upstream, under each flow condition we stimulated fish from each of three different attack directions relative to flow: aligned with flow (i.e., cranial), perpendicular (i.e., from the side), or aligned opposite to flow (i.e., caudal). Analysis of effect sizes indicated that there are strong effects of flow conditions and attack direction on the frequency of response failure across treatments. Juvenile S. stimpsoni had uniformly high response rates for attacks from a caudal direction (opposite flow); however, response rates for attacks from a cranial direction (matching flow) decreased dramatically as flow speed increased. Bow waves from predators attacking with flow might be masked by the flow environment, impairing attack detection by the lateral line systems of prey. Thus, the likelihood of successful escape performance in fishes can depend critically on environmental context, including water flow. Future studies will evaluate whether predators in this system take advantage of stimulus dampening by attacking prey in the same direction as ambient flow.
