Doppler sonar records of fish movement through a strong tidal stream: 3-months of observations from Grand Passage Nova Scotia

Abstract

Coastal passages with strong tidal streams present potential for renewable energy generation with in-stream hydrokinetic turbines. However, there are concerns that these systems will lead to environmental impacts when marine life interact with moving turbine blades. We explore measurements of fish movement using Doppler current profilers as a way of quantifying the frequency of such interactions. Fish are detected in Doppler sonar data using calibrated backscatter levels in each of the four acoustic beams; by reprocessing un-averaged data it is possible to extract both fish and water velocities independently. We analyzed three months of Doppler sonar data collected in Grand Passage Nova Scotia from September until December 2014. The data show fish detections in large numbers for only a few days on three occasions at the deployment site. Most of the observations show fish moving at the same speed as the water but there are times when there is significant difference in fish and water speeds.