Mobile Hydroacoustic Fish Survey In Upper Cook Inlet 2009 In Support of a Tidal Energy Project

Ocean Renewable Power Co. Alaska, LLC, is applying to the Federal Energy Regulatory Commission for a pilot license to conduct a tidal energy demonstration project in Upper Cook Inlet. Addition of any anthropogenic structure in the water column, including the deployment of underwater tidal turbines, has the potential to effect marine life. This survey was conducted to provide site-specific information on fish distribution and relative abundance within the water column in the vicinity of the proposed tidal project. Collecting fish data in the harsh environment of Upper Cook Inlet presents many challenges. The methodology developed in consultation with resource agencies consisted of three components: hydroacoustic surveys, target verification netting, and water quality sampling. The hydroacoustic component utilized two vessel-mounted split-beam hydroacoustic transducers in mobile surveys conducted during the ice-free season.  Each sample event consisted of three sub-surveys to evaluate tidal and diurnal patterns.  To assist in species identification and target validation, the hydroacoustic data was supplemented with fish collections using a gill net and trawl net. Ten data collection events were completed between May 28^th and October 5th, 2009. Hydroacoustic data was analyzed to identify spatial fish density with respect to diel and tide variables. Additionally, Aquacoustics Inc. developed GIS based cross-channel graphical models to demonstrate fish horizontal and vertical positions and fish size.  Fish densities in the survey area were very low overall, with peak densities of 39.6 fish/hectare estimated during spring sampling and a low density of 8 fish/hectare estimated in early September.  Spatial analysis indicates a strong pattern of higher mean fish density near shore.  Tidal influence was generally weak and variable.  The apparent diurnal pattern of higher densities at night was driven primarily by nearshore fish densities.  Further analysis of fish distribution by depth demonstrated that fish densities were higher in mid- to surface waters.  Test netting efforts were relatively ineffective due to weather, sea state, and tidal flow conditions, as well as low densities of fish. Commercial salmon data from Fire Island was used to supplement fish netting data.  The limited amount of fisheries information in marine waters of Upper Cook Inlet makes this a study of significance. The results will help stakeholders assess the potential impact to fish from underwater tidal turbines and contribute to the general body of knowledge for this important marine resource.