Passive acoustic detection of harbour porpoises in the Minas Passage
LE3 .A278 2013
Bachelor of Science
Tidal power development sites introduce potential risks to marine mammals. This project is focused on the acoustic detection of harbour porpoises (Phocoena phocoena) at the FORCE turbine test site in the Minas Passage, using two passive acoustic hydrophone technologies, the Chelonia Porpoise Detector (C-POD) and the icListenHF. Objectives of this study are to determine diel, tidal and lunar trends in porpoise activity and to compare the detection performance of the two hydrophone technologies under high flow conditions. Determining activity will help assess the potential risks of turbine interaction with porpoises. Comparing the performance of the two hydrophones in a high flow environment will help inform the design of marine mammal impact assessment studies. Range detection tests conducted in July 2012, using VEMCO acoustic transmitters, showed the icListenHF to have greater detection range than the C-POD. Two C-PODs and one icListenHF hydrophone were bottom moored at the same site in the Minas Passage for the entire month of August 2012. Detection positive minutes (DPMs) were used to indicate porpoise activity. There were more DPMs at night than during the day, and more DPMs on neap tides than spring tides. Ambient noise levels were highest during spring tidal cycles, and also higher during flood tides compared to ebb tides, causing interference with porpoise detection by both the icListenHF and C-PODs. On average, the icListenHF recorded nearly 10x more DPMs than the C-PODs. This aligns well with a listening volume that is 11x that of a C-POD. At very high current speeds the performance of both hydrophone types was limited by noise interference, most likely bedload transport. Improvements to the hydrophone technologies and how they are moored are recommended for more effective use in high flow environments.
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