A population of false killer whales, Pseudorca crassidens, in waters off northeastern New Zealand developed a relationship with bottlenose dolphins to defend themselves from predation, according to a 17-year study reported in the journal Marine Mammal Science.

False killer whales are one of the least studied species of ocean dolphin. The new study revealed that all 61 individuals in the area off the coast of New Zealand were linked in a single social network, while 88 per cent of identified individuals were re-sighted in the same area over several years.

Groups of false killer whales were also found to associate with bottlenose dolphins, Tursiops truncates. These partnerships were found to span more than five years and up to 650 km.

“The anti-predatory function of mixed species associations is mostly achieved through a greater chance of detecting a predator through more eyes watching out,” explained study lead author Dr Jochen Zaeschmar of Massey University, New Zealand.

“However, it is hard to say if this is mutualistic or parasitic, that is whether the two species actually co-operate or whether one just opportunistically exploits the detection ability of the other. Lastly, as both species are highly social, sociality may also play a role.”

“Given the level of site fidelity documented, a small and possibly closed false killer whale population in New Zealand waters cannot be ruled out. A reassessment of the current conservation status in New Zealand may therefore be prudent and further research warranted into the dynamics of this population,” Dr Zaeschmar said.

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Bibliographic information: Jochen R. Zaeschmar et al. Occurrence of false killer whales (Pseudorca crassidens) and their association with common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand. Marine Mammal Science, published online September 13, 2013; doi: 10.1111/mms.12065