COS 215-4 - Acoustic Ecology of Harbor Porpoise in the Northwest Atlantic Ocean

Abstract: The energy balance for any species is governed by the effort they expend to acquire food, the energetic value of that resource and how the energy acquired is utilized. Harbor porpoises (Phocoena phocoena) are small and inhabit the cold, temperate waters of the northwestern Atlantic Ocean. In order to cope with relatively cold waters they require close proximity to food supplies and need to feed regularly as they have limited energy reserves. Exposure to loud noises during offshore wind construction or nonlethal entanglement in fishing gear have been shown to negatively affect their time spent foraging and hence their survival. Information on their habitat usage and foraging ecology is invaluable in areas subject to rapid industrial expansion, such as along the coastal waters of the eastern United States. While broad scale abundance and density estimates are available for harbor porpoise from visual surveys, detailed information on their movements and behavior is still missing. Passive acoustic monitoring has shown to be a highly effective method for understanding long-term distributional patterns of harbor porpoise as they echolocate near continuously. Data from 10 echolocation-click detectors (F-PODs) over a 2-year period from 2020-2022 were analyzed to investigate spatial and temporal variation in the occurrence and foraging activity of harbor porpoise from inshore Gulf of Maine to Southern New England waters. The FPODs come with an onboard click classifier that is specifically designed to classify the narrow-band high-frequency clicks harbor porpoise emit during foraging and socializing. The dates and times of these clicks were extracted using FPOD software (Version 1.0) and were summarized into porpoise positive minutes for echolocation clicks and buzz positive minutes for foraging and social clicks. Porpoises were present year round in the Gulf of Maine with peak detections in the summer and fall, while porpoise clicks increased in Southern New England waters in the fall and winter, but were largely absent in the summer. One site in the Gulf of Maine, Mount Desert Rock (MDR), was an outlier with unusually high activity in winter. Foraging comprised 29% of all clicks with the most foraging detected at the MDR hotspot (53%). Results suggest that month, hour of day, and temperature are significant contributors to porpoise presence and foraging effort. This improved understanding of occurrence and foraging effort across these regions highlights the need for seasonal and regional protections to reduce impacts on this species.