Summary
Between January and April over six consecutive years (2000 to 2005) photographs of the dorsal fin and lateral bodies of pygmy blue whales (Balaenoptera musculus brevicauda) were collected at the Perth Canyon, Western Australia. The morphology was sufficiently variable to enable individual recognition and from 1600 survey hours (mean = 266 hours each year) 208 individuals were identified from the 271 photographed sightings. Twenty-three individuals were resighted between years but only two whales were resighted in three or more of the six years. A POPAN open population model estimated the population size to be 569 and 1,147 individuals. A closed, time-dependent, model with individual heterogeneity yielded a population size estimate of 712 to 1,754 individuals. We consider additional photo-ID data from Geographe Bay (Western Australia) and the Bonney Upwelling (southern Australia) to assess the likelihood that these population size estimates relate to the proposed pygmy blue whale population in the eastern Indian Ocean and Australian waters. Finally we outline future studies that could increase the precision of abundance estimates and delineate population boundaries.