Potential impacts of the Deepwater Horizon oil spill on sperm whale foraging ecology and movements

The 2010 Deepwater Horizon oil spill released a complex mixture of hydrocarbons and dispersants into the northern Gulf of Mexico (GoM), generating a subsurface oil plume that overlapped the primary foraging depths of sperm whales Physeter macrocephalus and their deep-sea cephalopod prey. To investigate potential shifts in movements and foraging ecology, we integrated satellite telemetry with bulk and compound-specific stable isotope analyses of amino acids from skin tissues collected before and after the spill. Telemetry data suggested that post-spill, both sexes continued to rely on northern GoM habitats, underscoring the region’s ecological importance. However, males reduced deep-abyssal movements and increased use of continental slope areas previously dominated by females, who concurrently exhibited increased site fidelity and a narrower isotopic niche width. Isotopic mixing models suggested a post-spill decline in the estimated contribution of cock-eyed squid Histioteuthis spp. for males, coupled with increased estimated contributions from Chiroteuthidae and Pholidoteuthidae taxa. Females maintained a consistent reliance on cock-eyed squid, while both sexes showed equally reduced estimated contributions from vampire squid Vampyroteuthis infernalis post-spill. Although region-wide pre- and post-spill comparisons on cephalopod abundance, composition, or distribution remain limited, the overlap among sperm whale core habitat use, foraging depths, and the deep oil plume is consistent with a potential shift in prey availability or quality, though natural interannual variability cannot be ruled out. These findings highlight the importance of long-term monitoring of apex predators and their prey in increasingly industrialized deep-sea ecosystems.