Using drifting passive echolocation loggers to study harbour porpoises in tidal-stream habitats

• Published in: Endangered Species Research
• Main Authors: Wilson, Ben, Benjamins, Steven, Elliott, Jim
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Phocoena phocoena; Tidal stream; Marine renewable energy; Survey; Methodology; Drifter; Harbour porpoise; Marine Mammal Monitoring
• Online Access: https://pure.uhi.ac.uk/en/publications/5f0f6929-2ff1-41df-93e8-163bc42e9d86; https://doi.org/10.3354/esr00538; https://pureadmin.uhi.ac.uk/ws/files/1353118/Wilson_et_al_13_Drifting_Porpoise_Detectors_in_Tidal_Streams.pdf; http://www.int-res.com/articles/esr_oa/n022p125.pdf

Moored passive acoustic detectors (e.g. C-PODs) are widely used to study harbour porpoise Phocoena phocoena distribution and relative abundance, but their use in tidal-stream habitats is complicated by the need for retrievable flow-resistant seabed fixings and the occurrence of flow-induced noise in the resultant data. In this study, we explored the use of a new method aimed at tidal-stream habitats, which are of increasing interest for marine renewable energy generation. Porpoise detectors (C-PODs) were attached to multiple drifters and repeatedly set adrift at a tidal-stream site in western Scotland during May 2010 and August 2011. Porpoise vocalisations were successfully detected under varying tidal conditions during approximately 63 h of drifting. Harbour porpoise distribution, as determined by the drifting detectors, was similar to that found using the traditional, yet more logistically intensive, visual and acoustic boat-based surveys and to an extent that found by moored C-PODs. Drifting detectors also mapped tidally driven spatiotemporal variability in ambient noise levels which could influence porpoise detection. In summary, drifters equipped with passive acoustic detectors offer a new, rapid and inexpensive tool for investigating porpoise occurrence and behaviour in tidal-stream habitats, and should be considered as part of a comprehensive marine mammal monitoring approach of these energetic environments in the context of marine renewable energy development and other industries.