Records of Australian humpback dolphins (Sousa sahulensis) from an offshore island group in Western Australia

Holly C Raudino,Kelly A Waples,Tim N Hunt

doi:10.1186/s41200-018-0147-0

Abstract

We report records of humpback dolphins at the Montebello Islands (20°26’S, 115°33′E) approximately 80 km from the mainland coast of Western Australia. This island group is a marine protected area (MPA), with approximately half of the area a sanctuary (no take) zone managed solely for nature conservation that excludes activities such as fishing and resource extraction, activities known to impact dolphins elsewhere. The habitat varies but includes fringing coral reef and shallow, sheltered sandy lagoons mostly < 10 m water depth and not exceeding 20 m. Several opportunistic sightings and one targeted five-day survey have resulted in 28 dolphins being catalogued in the MPA through photo-identification of natural marks on the dorsal fin and are considered to be recognisable through either distinctive or subtle marks. The species was initially reported in the MPA in June 2015 and was present in summer, autumn and winter of 2017. Six calves have been observed in the MPA, with one a neonate. Given the recent listing of the species as Vulnerable on the IUCN Redlist, and increasing pressure on near-shore coastal habitat, recognising the presence of this species at offshore islands such as these, and understanding their status and connectivity is a priority for the conservation and management of the species in Western Australia.

Highlights

The Australian humpback dolphin (Sousa sahulensis) was recently recognised as a separate species to the Indo-Pacific humpback dolphin (Sousa chinensis)
There have been few studies of the species’ distribution and abundance in Western Australia, with the exception of some intensive surveys in the coastal waters of the Kimberley (Brown et al 2016a, 2016b) and around the North West Cape in the Pilbara (Hunt et al 2017) where sightings were recorded within a few kilometres of the mainland coast and nearshore islands
Twelve opportunistic sightings of 39 dolphins were recorded between June 2015 and July 2017 including photographs, details on group size, composition and location (Fig. 2)

Summary

Introduction

The Australian humpback dolphin (Sousa sahulensis) was recently recognised as a separate species to the Indo-Pacific humpback dolphin (Sousa chinensis). There have been few studies of the species’ distribution and abundance in Western Australia, with the exception of some intensive surveys in the coastal waters of the Kimberley (Brown et al 2016a, 2016b) and around the North West Cape in the Pilbara (Hunt et al 2017) where sightings were recorded within a few kilometres of the mainland coast and nearshore islands.

Results

Conclusion