Abstract
The environmental effects monitoring program for tidal energy development at the Fundy Ocean Research Center for Energy test facility in Minas Passage requires examination of the effects on marine life, and includes Atlantic harbour porpoise, Phocoena phocoena (Linnaeus, 1758). All prior passive acoustic studies of porpoises in Minas Passage have used stationary, bottom-moored acoustic recorders (CPODs and icListenHF). Flow noise and noise associated with moorings and mobile sediments were identified as major issues for the acoustic detection of porpoises. The present study employed a custom designed drifting hydrophone (icListenHF) array to mitigate the effects of flow noise and moorings on passive acoustic harbour porpoise monitoring. The drifting array was deployed for a 5-7 hour drift on each of six days during 12th-27th June 2017. Harbour porpoise presence and behaviour, detected using the newly developed Coda click detector, was assessed in Minas Passage and adjacent areas. The effects of short-duration anthropogenic noise from fishing vessels and other boat traffic were found to have no observable effect on porpoise presence. The multi-hydrophone array detected porpoise clicks generated both above and below 15 m. Spatio-temporal and current speed patterns in porpoise activity were observed, with porpoise activity being lowest in Minas Basin, during early afternoon (1500-1700 UTC), and when current speed was <1m/s. The Coda detector was effective in identifying three behavioural modes in the harbour porpoise inter-click interval data. These were classified as feeding, searching and navigation trains. A novel finding was patterned clusters of clicks in most feeding trains and in 25% of search trains. This study will serve to inform future use of drifting hydrophone arrays for assessing harbour porpoise presence, abundance and behaviour in Minas Passage and, potentially, at high flow sites elsewhere.