Comparing optical camera and imaging sonar observations of animal interactions with a tidal turbine

Abstract

The potential for animal injury or mortality because of collisions with operating current energy turbines remains an important research question with consequences for management of proposed marine energy projects. During a 141-day deployment of a small-scale (1 m²) tidal turbine, a sensor package including optical cameras and imaging sonars was used to record near-field interactions between animals and the turbine. Over 1000 animal interactions were captured by the optical cameras, including several species of fish, at least two species of diving birds, and harbor seals (Phoca vitulina). Both seals and fish were observed in the vicinity of the turbine while it was rotating, and a range of behaviors were captured. Seals and fish were also observed while the turbine was stationary, although the observed behaviors were different. Diving birds were observed regularly, but only during daytime hours and when the turbine was stationary. In this work, we summarize trends in animal behavior with respect to tidal elevation, time of day, and turbine operational state and discuss specific observations of collisions (only observed for fish), evasion (fish and seals), avoidance, and attraction. Previously published analysis focused on optical camera data due to their ability to resolve near-field interactions with the rotor. Here, co-temporal sonar data are used to provide additional context that includes capturing a higher degree of animal presence near the operating rotor than determined in review of the optical data, documenting additional examples of avoidance and evasion behavior using the larger field of view, and providing evidence of predator/prey interactions that may inform collision risk. Based on our experiences and findings we also recommend approaches for future projects seeking to acquire, analyze, and report on similar data sets.