A comparative analysis of bottlenose dolphin and harbour porpoise foraging patterns in Jersey, Channel Islands

This study investigated bottlenose dolphin and harbour porpoise spatial and temporal foraging patterns in the Channel Islands, with a particular focus on Jersey’s waters. Through analysis of cetacean foraging behaviours using Chelonia’s Full-Waveform Capture Porpoise Detector (FPOD) devices deployed at eight sites, aiming to provide insights supporting informed conservation strategies. The study employed Generalised Linear Mixed Models (GLMM) to assess spatial, temporal, and seasonal variations in cetacean behaviour and the impact of boat sonar on detections. Findings indicate that harbour porpoises are primarily present in Jersey water’s during winter and their presence is localised to Plemont, a key foraging site, while bottlenose dolphins exhibit peak foraging activity during summer, preferentially foraging at the Minquiers. Both species forage more intensively in the evening, and their presence was negatively affected by sonar, with harbour porpoises being particularly sensitive. Although, variability in sampling effort and seasonal data gaps at some sites indicate that future research should focus on under-sampled sites, such as offshore reefs, to improve understanding of foraging patterns. The study underscores the importance of targeted conservation measures to protect critical foraging areas and mitigate human impacts, aligning with international agreements and local conservation policies.