Harbor porpoises are known to frequent the area known as the “Great Race” of the Gulf of Corryvreckan, a high-energy tidal stream. This study monitored harbor porpoise distribution relative to tidal cycles and speeds using static (C-PODS) and drifting passive acoustic detectors at this potential tidal site.
Support was provided by the UK Natural Environment Research Council (NERC) under grants NE/H009299/1 (Great Race Project) and NE/J004367/1 (RESPONSE), and by the Scottish Government, Highlands & Islands Enterprise (HIE) and the European Regional Development Fund (ERDF) under the MaREE grant (RE011).
Gulf of Corryvreckan, Scotland, UK
To combine Eulerian and Lagrangian techniques to explore small-scale spatiotemporal variability in the distribution of vocalising harbour porpoises in relation to tidal currents.
C-PODs moored in the path of the Great Race registered a significant increase in detections during the passing of the energetic tidal jet. Encounter durations recorded by drifting C-PODs were longer than those recorded by moored C-PODs, suggesting that porpoises tended to move downstream with the flow rather than remaining stationary relative to the seabed or moving upstream. The energetic, turbulent conditions of the Great Race are clearly attractive to porpoises, and they track its movement with time; however, their structured movements in response to the evolving tidal situation cannot simply be represented as a direct relationship between current speed and porpoise presence.
Benjamins, S.; Dale, A.; van Geel, N.; Wilson, B. (2016). Riding the Tide: Use of a Moving Tidal-Stream Habitat by Harbour Porpoises. Marine Ecology Progress Series, 549, 275-288.