COS 136-3 - Acoustic Ecology of sperm whales (Physeter macrocephalus) around wind energy areas in the northwestern Atlantic Ocean

Abstract: Sperm whales (Physeter macrocephalus) are an apex predator in marine ecosystems, renowned for their deep diving capabilities to forage on squid. Classified as Endangered under the US Endangered Species Act, their habitat usage and demographics are poorly understood throughout many regions of the northwestern Atlantic Ocean undergoing rapid wind energy development. Sperm whales use distinct clicks, termed “usual clicks”, to echolocate during foraging. The interclick interval (ICI) of these clicks can be used as a proxy for body size to categorize population structure. For example, the ICI of mature males is typically >0.8 s, ICIs between 0.6 and 0.8 s represent mid-size individuals (either adult females or bachelor males), and ICIs < 0.6 s represent social groups comprising a mix of females and juveniles.

In 2020, four passive acoustic recorders (SoundTrap 600; sampling at 48 or 64 kHz) were deployed at two sites on Nantucket Shoals (NS) and two sites on Cox’s Ledge (COX) in the Southern New England wind energy area. They were deployed in shallow waters (< 42 m) from either January or November 2020 to November 2022. A click detector was run in Matlab (2016b) using the Triton program to identify sperm whale clicks, which were then manually verified using the detEdit program. Custom Matlab scripts calculated ICIs, and binned them into five minute intervals to obtain the dominant ICI required for determining demographic groups. A simple propagation model was constructed within Matlab to understand the detection range at each site.

Results suggest that sperm whales were only occasionally detected at the COX sites (on 0.4% and 1.3% of days analyzed), with most of those detections occurring in October (75%). At the NS sites, sperm whales were detected more often (on 9.6% and 11.4% of days analyzed), and mainly between May and August (85% of days with detections). During the months with consistent presence on Nantucket Shoals, social groups, midsize animals, and mature males were detected across all months. Social groups and mature males were present within the same hour on 26% of the days analyzed. Although detections were rare, all three groups were also detected at the COX sites. All sperm whale demographic groups used the wind energy area across multiple seasons with their peak use occurring between spring and autumn, identifying the Southern New England wind energy areas as important habitat for sperm whales.