Movements of sperm whales in the tropical Pacific

The movements of female and immature sperm whales Physeter macrocephalus in the tropical Pacific Ocean and adjacent waters are described using photoidentifications over time scales of 3 d to 15 yr and the tracks of followed groups over scales of 1 to 48 h. The female/immature whales frequently made movements of less than 2000 km and occasionally made movements of about 4000 km. There were no recorded movements of greater than 5000 km (for instance, between the eastern and western Pacific). On average, displacements for female/immature whales were about 4 km after 1 h of movement, 50 km after 1 d, 200 km after 3 d, and 1000 km after periods of 1 yr or more. Members of the 2 principal cultural clans of female and immature sperm whales that use waters near the Galapagos had distinctive movement patterns over all time scales greater than 3 h, with 1 clan's displacements about 50 % greater than the displacements of the other. Displacements were greater than predicted by the correlated random walk over scales of 12 to 48 h because of auto-correlation in displacement, approximately as predicted by the correlated random walk over periods of days to weeks, but less than predicted by the correlated random walk over scales of years because of boundaries of home ranges. The adaptive movement of sperm whales over large spatial and temporal scales likely contributes to their substantial trophic impact, and reduces geographic population structure. These movements, together with cultural heterogeneity, complicate the management of the species, including the designation of management stocks.