PNNL

Abstract

A diversified national energy portfolio may include marine energy in the form of current energy converters (CECs) such as tidal or in-river turbines. New technology in the research stage typically requires monitoring for environmental effects. A significant environmental effect of concern for CECs is the collision risk of moving parts (e.g., turbine blades) with animals such as fish. CECs are installed in energetic locations in which it is difficult to operate sensors to fulfill monitoring requirements. Collecting data that inform direct interactions, such as blade strike or near-miss, of fish with CECs is usually attempted using active acoustic sensors or video cameras. Limitations of low-light conditions or water turbidity that preclude video camera use are overcome by using high-resolution multibeam echosounders (referred to here at acoustic cameras). We used a Sound Metrics ARIS 3000 acoustic camera at two sites to test its ability to detect artificial and real fish targets and determine if strike, near-miss, and near-field behavior could be observed. The first site was a tidal channel with a 25 kW turbine and water clarity good enough to allow video camera data to be collected with acoustic camera data showing turbine blade strike on a tethered artificial fish target. The second site was a turbid, debris-laden river with a 5 kW turbine where only acoustic camera data were collected due to high water turbidity. Data collection was aimed to coincide with downstream Pacific salmon smolt (natural fish targets) migration to gather fish interactions with the turbine. Few natural fish targets were observed though nearby fyke net catches indicated smolts moving downstream during acoustic camera data collection. Of the targets observed in acoustic camera data, few showed non-passive movement, making their separation from debris difficult.