Bachelor sperm whales (Physeter macrocephalus) in The Bahamas: Insights from a multi-disciplinary study
Presented by Charlotte Dunn
Charlotte Dunn, Kim Parsons, David Herman, John Durban, Gina Ylitalo, and Diane Claridge
There is little information regarding the lives of subadult male sperm whales (Physeter macrocephalus) between their dispersal from their natal group and subsequent arrival in higher latitudes where they live primarily solitary lives. We integrated a suite of approaches in the field and laboratory to elucidate the occurrence and composition of bachelor sperm whales in the Bahamas. Acoustic analysis from 8 of 21 genetically sexed male sperm whales resulted in size estimates comparable to subadult male sperm whales in other regions (range 8.2–13.4m); field observations and photographs place the remaining males within this same size category. Using photo-identification data, pairwise association indices between males across years (mean=0.02 (sd 0.02), max=0.33) provided support for occasional formation of “bachelor groups”. Genetic pairwise analysis from biopsied individuals revealed that the level of relatedness between males was comparable to pairwise relatedness of genotyped adult females from this region (pairwise results: 0.046 SM, n=21; 0.062 AF, n=18). However, on average subadult males are more closely related to one another than to adult females, suggesting these males may be immigrants. Inference from satellite transmitter tags (n=27), chemical markers (n=54 biopsies) and photo-identification data also indicated that subadult males have larger ranging patterns than these females. The majority of bachelors were tracked using a deep oceanographic trough (Tongue of the Ocean, TOTO), while adult female groups and their calves rarely use this area. Notably, TOTO is the site of a US naval underwater testing range, and a tagged sperm whale reduced its’ surface time by 50% during a multi-ship exercise using mid-frequency active sonar in TOTO. Bachelor whales have been re-sighted in TOTO across years so may be repeatedly disturbed during an important period of growth in their lives. These novel findings increase our understanding of the lives of bachelor sperm whales.