Occurrence of false killer whales (Pseudorca crassidens) and their association with common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand

Abstract

On a global scale, false killer whales (Pseudorca crassidens) remain one of the lesser‐known delphinids. The occurrence, site fidelity, association patterns, and presence/absence of foraging in waters off northeastern New Zealand are examined from records collected between 1995 and 2012. The species was rarely encountered; however, of the 61 distinctive, photo‐identified individuals, 88.5% were resighted, with resightings up to 7 yr after initial identification, and movements as far as 650 km documented. Group sizes ranged from 20 to ca. 150. Results indicate that all individuals are linked in a single social network. Most observations were recorded in shallow (<100 m) nearshore waters. Occurrence in these continental shelf waters is likely seasonal, coinciding with the shoreward flooding of a warm current. During 91.5% of encounters, close interspecific associations with common bottlenose dolphins (Tursiops truncatus) were observed. Photo‐identification reveals repeat inter‐ and intraspecific associations among individuals with 34.2% of common bottlenose dolphins resighted together with false killer whales over 1,832 d. While foraging was observed during 39.5% of mixed‐species encounters, results suggest that social and antipredatory factors may also play a role in the formation of these mixed‐species groups.

A preliminary study of the movement patterns of false killer whales (Pseudorca crassidens) in coastal and pelagic waters of the Northern Territory, Australia

“…A notable exception to this general pattern is the genetically distinct nearshore false killer whale population that occurs around the main Hawaiian Islands; however, this population mostly occurs in deep waters (.500 m) and uses shallow (,100 m) waters only occasionally (Baird et al 2008(Baird et al , 2010(Baird et al , 2012Martien et al 2014). Perhaps a habitat use more similar to that reported here is the recent recognition of use by false killer whales of shallow continental shelf habitats off Costa Rica (Douglas et al 2011), northern New Zealand (Zaeschmar et al 2014), and in the eastern tropical Atlantic off western Africa (Weir et al 2013).…”

Behavioural Effects of Tourism on Oceanic Common Dolphins, Delphinus sp., in New Zealand: The Effects of Markov Analysis Variations and Current Tour Operator Compliance with Regulations

“…Similarly to bottlenose dolphins [ 99 , 100 ], movements of some common dolphins across neighbouring regions in the North Island have been confirmed [ 101 ]. Indeed, several individuals identified in the Hauraki Gulf have previously or subsequently been observed in the Bay of Islands or in the BOP, 200km further north and south east, respectively [ 102 ].…”

Long-term responses of Burrunan dolphins ( Tursiops australis ) to swim-with dolphin tourism in Port Phillip Bay, Victoria, Australia: A population at risk

“…Smaller groups may see tour vessels as a potential threat, and hence avoid tour vessels more frequently than larger groups. Delphinids often form larger groups in situations of threat or danger, in an attempt to provide increased vigilance and predator protection via group defence (Gygax, 2002;Zaeschmar et al, 2014). Hence, dolphins travelling in larger groups in PPB may perceive potential threats, such as tour vessels, as less threatening than small groups, explaining the higher approach rate to tour vessels by large groups.…”