Marine renewable energy (MRE) devices potentially impact dynamics of aquatic organisms including macroinvertebrates, fish, seabirds, and marine mammals. Understanding potential impacts of MRE technologies on biological communities requires knowledge of species-specific spatial and temporal density distributions. Acoustic technologies capable of providing images and data for baseline characterizations and operational monitoring are commercially available but configurations and system integration for MRE applications have not been established nor evaluated. Deployment, operation, and retrieval of autonomous acoustic instrument packages are also complicated by extreme water flows at MRE sites. At a proposed tidal energy site in Puget Sound, Washington, USA, an echosounder, multibeam sonar, acoustic camera, and an Acoustic Doppler Current Profiler (ADCP) were deployed on bottom during May and June, 2011. To provide a spatial characterization of the biological community at the site, a vessel-mounted echosounder and pelagic trawl were used to map fish and macrozooplankton densities during day, dusk, and night surveys. Marine mammals and seabirds were identified and counted during surveys. The primary objective of the project was to compare sampling capabilities of surfaceand bottom-deployed acoustic instruments.
Our field work confirmed that autonomous instrument sampling is more constrained by power than by data storage; that direct sampling in high flow environments is a challenge; and that limited direct samples constrain acoustic target classification. A suite of metrics successfully characterized vertical distributions of aquatic organisms in the water column. Results showed that surface and bottom deployed echosounders detected horizontal and vertical density changes that were correlated with environmental covariates. Metric values from the acoustic camera and ADCP data were not as sensitive to changes in density.
Current acoustic technologies can be configured and used to characterize aquatic organism distributions at MRE sites. Integrated acoustic instrument systems that include target tracking and impact warning do not exist in autonomous or cabled configurations. Development of algorithms to translate temporal to spatial variance and to scale observed effects from pilot to commercial site domains is needed to complete the ability to monitor change and to detect impacts on biological communities for MRE site monitoring