Emaciation and marine debris contribute to sperm whale Physeter macrocephalus strandings in southeastern USA: comparing 4 cases from 2020-2022 Diseases of Aquatic Organisms

Large whale strandings along the east coast of the USA have increased in recent years, resulting in unusual mortality event (UME) declarations for several species. Endangered sperm whales Physeter macrocephalus have not been included in a UME; however, recent strandings have shown commonalities that warrant investigation. We analyzed 4 live-stranded sperm whales (‘case’ whales) in waters of the southeastern USA from 2020-2022 to determine if common factors contributed to death and to inform future management decisions. Thorough investigations were performed, including necropsy, histopathology, and infectious disease and biotoxin testing. Major findings were related to emaciation; there was no evidence of infectious disease or significant toxin exposure. Two of the whales had ingested fishing gear and other marine debris that may have contributed to emaciation. Prey identification and stable isotope analysis (SIA) of these whales combined with SIA of 4 additional sperm whales (‘reference’ whales) provided further life history data for this species. Prey consumed were primarily cephalopods from families consistent with known sperm whale diets in other parts of the world, and SIA suggested that case whales had similar foraging habitats and trophic levels compared to reference whales. The common finding of emaciation in case whales despite typical prey consumption emphasizes the need for continued research on factors that may influence foraging efficiency or prey availability and quality in this region. Furthermore, finding ingested fishing gear in 2 whales supports continued efforts to monitor and mitigate human impacts to support long-term survival and recovery of sperm whale populations.