Oceanic bottlenose dolphins (Tursiops truncatus)
Oceanic bottlenose dolphins (Tursiops truncatus)Two forms of bottlenose dolphin occur in New Zealand waters; a widely studied nationally endangered coastal form and a little known oceanic form. Our oceanic bottlenose dolphin research programme was initiated in 2005 as a photo-identification study, investigating the extent and possible functions of the frequently observed associations between oceanic bottlenose dolphins and false killer whales. Our study documented long-term associations between individuals of both species spanning over 10 years and hundreds of kilometres. While similar associations likely occur in other parts of the world, our study remains the only one to show long-term associations between individual members of two different cetacean species. The exact extent and possible functions of these associations are the focus of ongoing behavioural studies.
Our research shows that oceanic bottlenose dolphins also associate with pilot whales, although there appear to be differences in the extent and purpose of these association compared to those observed with false killer whales. While oceanic bottlenose dolphins can also be seen in heterospecific groups, these appear to be significantly less frequent than the mixed-species groups that we have documented.
Similar to our false killer whale findings, our research shows that oceanic bottlenose dolphins occur regularly in the coastal waters off north-eastern New Zealand and that their home-range overlaps with that of the coastal form in a number of places. Results further suggest that the oceanic population is considerably larger than that of the coastal form that appears to be in decline in some areas. To answer important questions about the population dynamics of the coastal form, our current research is focusing on the extent of possible interchanges between the two forms using photo-identification and genetic sampling. Our oceanic bottlenose dolphin programme is the first study of this ecotype in New Zealand and results will help to place the coastal population into a wider context. As such, it will provide important information for appropriate management strategies for both ecotypes.