Distribution of Irrawaddy dolphins, Orcaella brevirostris, in Australian waters

Abstract

Records from strandings, museum specimens, sighting databases and unpublished sightings of aerial surveys were compiled and used to review the distribution and population status of Irrawaddy dolphins, Orcaella brevirostris, in Australian waters. Stranding and museum specimen records indicate that Irrawaddy dolphins occur only in the northern half of Australia, from approximately the Brisbane River (27° 32'S, 152° 49'E) on the east coast to Broome (17° 57'S, 122° 14'E) on the west coast. Aerial surveys demonstrate that Irrawaddy dolphins occur mainly in protected, shallow, coastal waters, close to river and creek mouths, which appear to be an important habitat for the species. Irrawaddy dolphins tend to form relatively small groups of 1-10 animals with occasional aggregations of up to 14 animals. The status of Irrawaddy dolphins in Australian waters is difficult to assess, because most data have been collected opportunistically. However, the low number of sightings during aerial surveys, in comparison with observations of other sympatric marine mammals, such as Indo-Pacific humpback dolphins (Sousa chinensis), suggest that Irrawaddy dolphins are relatively uncommon in Australian waters. or possibly are inadequately sampled on aerial surveys.