Assessment of attraction and avoidance behaviors of fish in response to the proximity of transiting underwater vehicles

Underwater vehicles have many advantages for sampling fish; however, estimates can be biased by behavioral responses to sampling gear. To evaluate avoidance and attraction bias we assessed changes in fish abundance relative to a variety of sampling vehicles during transit through a test bed. Fish species were classified into five attraction and avoidance categories according to the behavioral responses exhibited. We observed that the rigor of behavioral responses varied by vehicle, vehicle range and altitude, transect number, and habitat complexity. The effect of each variable is dependent on behavioral guild, but vehicle range was the most consistent predictor of changes in abundance regardless of vehicle. Vehicles that surveyed the environment at higher relative altitudes off the seafloor and at slower speeds elicited weaker behavioral responses regardless of whether those reactions were attraction or avoidance. The testbed approach allowed assessment of responses that cannot be observed from the perspective of a sampling vehicle but was restricted by the number of species-specific interactions observed. Despite success in estimating behavioral responses, calibrating the effect against known densities of fish was not possible. However, the method used is a robust way for future investigations to quantify species-specific responses for gear calibration and to provide information that aids in the calculation of fish abundance.