Abundance and seasonal residence of sperm whales at Kaikoura, New Zealand

Abstract

Photographic identification was used to document patterns of occurrence of individual sperm whales in the deep nearshore waters off Kaikoura, New Zealand. Between 1988 and 1993, 86 individuals were identified from nicks and marks in the trailing edge of their flukes. All individuals photographed were uniquely identifiable and no substantial changes in mark occurred over the study period. Resightings show that some whales spend several weeks or months in the area. Half have been seen in more than one field season. One individual has been seen every year from winter 1989 to winter 1992, and like several others appears to return to the area regularly. Others (35%) have been photographed on 1 day only and may be transients. Almost all (88%) of our sightings were of single whales. We used "open" capture–recapture models to estimate the size of the population that visits Kaikoura. These models suggest an average population of between 60 and 108 individuals present in any one season.