False Killer Whales Pseudorca crassidens: Regular Visitors to Port Essington and Darwin Harbour in the Northern Territory, Australia

Abstract

Until recently there has been very little cetacean research undertaken in the Northern Territory (NT) (Chatto & Warneke 2000; Palmer et al. 2009). However, since 2007 the Coastal Dolphin Project has been focussing on the three species of coastal dolphins (Australian Snubfin Orcaella heinsohni, Indo-Pacific Humpback Sousa chinensis and Indo- Pacific Bottlenose Tursiops aduncus) and undertaking a range of research activities including monthly boat-based surveys at three sites in the NT: Coburg Marine Park, Darwin Harbour and the Alligator Rivers region. As the Coastal Dolphin Project has gained a profile both publicly and within various government agencies and nongovernment organisations, a further benefit has been the recording, reporting and collation of information on a typically ocean-going dolphin that appears to be a regular visitor to both Port Essington and Darwin harbours, the False Killer Whale Pseudorca crassidens. The False Killer Whale is one of the larger members of the dolphin family, Delphinidae, and despite its world-wide distribution throughout the tropics and subtropics, is one of the least known of the large tropical oceanic dolphins (Odell & McClune 1999) (Table 1). Adult male False Killer Whales can reach up to 6 m in length and females to 5 m (Baird 2008). The common and scientific names relate to the similarity in skull morphology to the Killer Whale (Orcinus orca), but the two species are not closely related. In most parts of their range, False Killer Whales are usually far from shore, though there have been occasional exceptions, and individuals have been recorded on the west coast of Vancouver Island in Barley Sound, Canada (Stacey & Baird 1991). The only other areas where False Killer Whales are frequently seen close to the shore are near tropical oceanic islands (Acevedo-Guitierrez et al. 1997; Baird et al. 2008). In particular, genetic evidence suggests a demographically isolated population around the main Hawaiian Islands (Baird et al. 2008; Chivers et al. 2007).