Cobscook Bay, Maine is well known for its strong tides. The mean tidal range is 5.7 meters and current speed can exceed 2 m·s-1 in the channel of the outer bay, which makes this area attractive for tidal power development . Extracting energy using marine hydrokinetic (MHK) devices is receiving growing global interest because of the environmental friendliness of the technology and the predictability of the tides. The MHK devices extract energy with moving parts which can result in a collision risk for fish if they cannot avoid /escape the moving parts. Although some studies have examine d the survival of fish passing through tidal turbines in laboratory flumes [2-3] and fish behavior in the near-field of a test turbine , the potential effects of MHK devices on fish remain unclear.
It is difficult to accurately predict the effects and impacts of MHK devices on fish because relatively few commercial-scale devices have been deployed. Ocean Renewable Power Company, LLC (ORPC) has taken a sequential approach to develop tidal power, beginning with the identification of potential development sites, establishment of a test site in Cobscook Bay, and the initial test deployment of two MHK devices. The two devices were deployed by ORPC during different periods: TidGen® from March 2012 to July 2013, and OCGen® from July 2014 to August 2014. The test turbines provided the opportunity to investigate fish reactions to MHK devices and estimate their encounter probability with the TidGen®.
The dynamic environment at tidal power sites precludes the use of most conventional biological monitoring tools. However, hydroacoustic techniques can work well in such environments [5-6]. To examine fish response to a single MHK device, we used two different hydroacoustic approaches: stationary down-looking surveys and mobile down-looking surveys. Stationary down-looking surveys were conducted at the site of the TidGen® device, and also at a control site about 1.75 km seaward from the project site (Figure 1). Mobile down-looking surveys were carried out at the project site only (Figure 1).