Developments to test TISEC devices and harness tidal energy from high flow sites in the Minas Passage require examination of the potential effects of tidal turbines on the environment, including impacts on marine mammals. Studies conducted to date, at and near the Fundy Ocean Research Centre for Energy (FORCE) in-stream tidal turbine test site in Minas Passage, have included passive acoustic monitoring (PAM) of harbour porpoises during late spring, summer and fall months (Tollit et al., 2011; Wood et al., 2013). This study reports on winter and early spring (Dec-May) baseline data on harbour porpoise pres-ence in Minas Passage during 2013-2014 and addresses both the winter data gap and the performance of different hydrophone technologies deployed in Minas Passage.
We conducted the winter/spring survey of marine mammals at multiple locations in and near the FORCE site during Dec 2013 – June 2014, with the use of C-POD porpoise detectors (Chelonia Ltd) and the icListenHF smart hydrophone (Ocean Sonics Ltd). Both technologies are non-invasive and continuously monitor harbour porpoise click trains within their operational detection range. The main objectives of this study were to close the seasonal (winter/spring) gap in data on harbour porpoise activity in Minas Passage and to determine detection range (distance from hydrophone) and performance in relation to varying tidal conditions for each of the hydrophone technologies examined.
Winter-spring data collected from SUB buoy mounted C-PODS at four of the prior PAM sites showed low presence during winter with activity increasing in March and peaking in June when Atlantic herring and other fishes are known to be present in high abundance. The new data were pooled with all previous C-POD data from the Minas Passage (2010-2012 dataset) prior to data analyses. A new GAM/GEE model was prepared with plots of covariates showing porpoise detection results in relation to Julian Day (sea-sonal trends), noise (as indicated by C-POD performance metrics - % Time Lost), day vs. night, location, tidal height and current speed. The full dataset (2010-2014) and revised statistical model provide year-round baseline conditions for comparison with studies that will be conducted following turbine installa-tion and operation.
In-field testing of hydrophone performance involved assessing the detection range of each device type (C-POD and icListenHF) housed in a weighted instrument platform resting on the bottom of the FORCE test site. A surface drifting speaker (icTalk, 120-140 kHz) was programmed to transmit at a set rate. All range test C-POD CP1 files and icListenHF spectrograms were visually inspected. C-PODs detected icTalk transmissions up to 300 m from the sound source, with detection efficiency (proportion of transmissions detected; also known as “recall”) greatest within 100 m. Detections, however, were uncommon at depth-averaged current speeds of >1m/s. Data files from a shrouded (20 ppi, ½ inch acoustic foam) icListenHF hydrophone, when visually analyzed by a human, showed icTalk transmission detections at distances up to 300 m (>30% icTalk transmissions detected), with 100% detection efficiency at distances up to 150m.
Harbour porpoise detections recorded by C-PODs housed on the platform were considerably greater than those shown for a co-located C-POD in a SUB buoy moored 2-3 m off the seafloor. Factors that appear to affect performance of SUB buoy mounted C-PODs include excessive tilt of the unit during high flow periods. Detection of non-target noise that results in % Time Lost was also greater for the SUB mounted C-POD. These tests of hydrophone performance inform the FORCE Environmental Effects Monitoring Program of the usefulness of sensor platforms in Minas Passage.