Decline

How do we know the population size?

Photo Identification – researchers take photos of every dolphin in the group, focusing in on their dorsal fin. The dorsal fin of a dolphin is as unique as a human finger print, allowing scientist to track individual dolphins movements. By creating a catalogue of fin and tracking re-sightings of individuals a population size can be calculated.

Is the decline due to death or leaving the area?

Distribution, habitat use and data-set comparison – the decline in the Bay of islands is likely due to emigration rather than mortality. Scientist believe this is the case as the North Island population is not declining at the same rate and individuals that are no longer using the bay of islands have been identified in other areas such as Doubtless Bay, Great Barrier Island and Whangarei Harbour.

Why does a decline in numbers matter?

Calf mortality, habitat use and sustainability – the Bay of islands provides a uniquely diverse habitat, which makes in an ideal nursery area for multiple marine mammal species. The calf mortality in the Bay of Islands, when linked with the behaviour changes notes and the population decline, is of huge concern for the sustainability of the population. When born in other areas of the North-east coast bottlenose dolphin calves are exposed to predators, colder waters and greater distances of travel to find key habitats. This all takes a toll on a growing calf and the mother trying to ensure their survival.