Alternate Title

Social Structure of Sperm Whales in the Northern Gulf of Mexico


Sperm whales exhibit highly structured social behavior that depends on sex, age, and possibly local ecological characteristics. We analyzed sighting data collected between 1994 and 2005 to determine the social structure of sperm whale groups in the northern Gulf of Mexico (714 good-quality photographs of 285 individual whales). Average typical group size was approximately eight when estimated with mark-recapture techniques and using data from 2003 to 2005. Lagged association rate analyses including data from 1994 to 2004 indicated average group sizes of 11.41. Therefore, groups in the Gulf are considerably smaller than groups in the Pacific Ocean, but similar to those from the Caribbean Sea. Similarly, groups in the Gulf of Mexico remained stable for longer periods (62.5 d, SE = 47.62) than Pacific groups, but were comparable to groups from the Gulf of California. Such differences and similarities between populations could be due to adaptations to local conditions, indicating that Gulf of Mexico sperm whales may live in ecological conditions more similar to those of the Caribbean and the Sea of Cortez than to the Pacific.