Seasonal distribution and diving behaviour of male sperm whales off Kaikoura: foraging implications

Abstract

Male sperm whales (Physeter macrocephalus) were the preferred target of the whaling industry between 1950 and 1985, but despite hundreds of thousands of kills, very little is known about their ecology. To partially redress this, we present data on residency, seasonal distribution, and diving behaviour of individually identified sperm whales off Kaikoura, South Island, New Zealand, gathered during 15 field seasons over 8 years. One hundred and thirty-six sperm whales were identified within the study area. A lack of statistically significant differences in the abundance of sperm whales between summer and winter, and among the 15 seasons of fieldwork, suggests an adequate food supply year-round. Significant differences in distribution between summer and winter suggest that off Kaikoura, male sperm whales may change their diet in response to fluctuations in prey biomass. Diving behaviour was also significantly different between summer and winter: sperm whales dived for longer, stayed longer at the surface, and travelled farther between consecutive fluke-ups in summer than in winter. Unlike female sperm whales, males at Kaikoura spent little time at the surface; they spent about 83% of their total time under water. This paper represent the most extensive non-invasive study of male sperm whales and provides new insights into their ecology.