New York Timeshare: Staggered Habitat Use of Small Cetaceans in the New York–New Jersey Harbour Estuary

Sympatric species that occupy similar niches use a variety of strategies to minimise competitive exclusion. Bottlenose dolphins and harbour porpoises are both small cetaceans that occur in coastal areas and, in many areas where there is overlap, have been shown to use the habitat in different ways or at different times. In the New York–New Jersey Harbour Estuary (NY–NJ Harbour Estuary), bottlenose dolphins and harbour porpoises are found seasonally. We used passive acoustic monitoring to compare the acoustic presence of dolphins and porpoises from October 2018 to October 2020 in the NY–NJ Harbour Estuary, which revealed spatiotemporal differences in habitat use between the two species. The peak in acoustic presence for bottlenose dolphins occurred during summer and autumn, while porpoises were primarily detected during winter and spring. Porpoises were more acoustically active during the daytime, with some variability across months, while dolphins were consistently more active at night. Generally, dolphins were more commonly detected than porpoises, but porpoises were detected more often in the Upper Bay where bottlenose dolphin detections were rare. Dolphins and porpoises were more acoustically active around ebb and slack tides, respectively. Establishing baselines for species occurrence and identifying possible ecological influences on spatiotemporal patterns is important and time-sensitive given current and forthcoming anthropogenic activities, including activities related to offshore wind development.