Exploring sperm whale population demographics in the northern Gulf of Mexico using passive acoustic monitoring

Abstract

Sperm whales are a sexually dimorphic species widely distributed throughout the world’s oceans, with social units of mature females and young thought to inhabit tropical and temperate waters, while individual mature males travel to higher latitudes in small bachelor groups or alone. Seasonal population demographics, particularly sex distributions, and the group structures of sperm whales have not been closely analyzed for the Gulf of Mexico. Utilizing the unique multi-pulse structure of sperm whale echolocation clicks, their total body length can be estimated, and, as a result of their extreme sexual dimorphism, their sex can be determined. Continuous acoustic recordings from June 2018 through June 2020 by the Environmental Acoustic Recording System (EARS) buoys, deployed off the coast of Louisiana, were analyzed using CABLE software [Beslin et al., JASA (2018)]. The results suggest that the sperm whale population is dominated by females in both summer and winter seasons, although mature whales of both sexes were detected in both seasons. Additionally, for each year of study, respectively, the mean size and the total number of whales detected were greater in winter months. Further insights into group structures will be discussed in the presentation. [Research supported by NSF REU (Award No. 1659853) and BOEM.]