Insights into the demographics and spatial distribution of sperm whales at Guadalupe Island, Mexico, from passive acoustics

Sperm whales (Physeter macrocephalus) are cosmopolitan cetaceans exhibiting sex-based differences in ecology and distribution. Sperm whales are present at Guadalupe Island (GI), Mexico, where tourism vessels employed ultrasonic antifouling (UA) devices through 2021. We investigated sperm whale presence and demographics near the island and examined their spatial distribution using signal amplitude distributions from a single-hydrophone system. Sperm whales were detected intermittently at GI between 2018 and 2022. We used inter-click intervals to determine demographic information. Male sperm whales were present year-round; social groups of females and young were generally scarce but increased in 2022. Using Monte Carlo simulations, we evaluated different spatial distributions of each demographic group to identify the typical locations that best explained observed click received levels at the recording station. On daily and weekly scales, no significant change in sperm whale acoustic presence was observed for periods with UA, contrary to findings for goose-beaked whales (Ziphius cavirostris). However, because the predicted spatial distributions of sperm whale habitat indicated minimal overlap with the reach of UA, it appears that their distribution may limit their exposure. This study highlights GI as an important habitat for male sperm whales and, potentially, an emerging seasonal habitat for social groups.