Abstract
The bottlenose dolphins of Fiordland, New Zealand, live at the southern limit of the species’ worldwide range. They are exposed to impacts from tourism and habitat modification, particularly in Doubtful Sound, and their conservation requirements are presently unclear. Dolphin abundance was estimated in Doubtful Sound using photoidentification census and capture-recapture techniques (56 individuals; 95% CI: 55-57), detecting a decline of 34-39% over 12 years among adults and sub-adults (>3 years old). The cause of this decline was investigated via demographic modelling in Doubtful Sound and a comparative assessment of population status in Dusky Sound.
Capture-recapture modelling of photo-identification data compiled since 1990 yielded a constant adult survival rate marginally lower than prior estimates for wild bottlenose dolphins (φa(1990–2008) = 0.9374; 95% CI: 0.9170-0.9530). Survival of calves (<1 year old) declined to an unsustainable level that is thought to be the lowest recorded for wild bottlenose dolphins (φc(2002–2008) = 0.3750; 95% CI: 0.2080-0.5782) coincident with the opening of a second tailrace tunnel for a hydroelectric power station. Reverse-time capture-recapture modelling detected declines in recruitment (f(1994–2008) = 0.0249; 95% CI: 0.0174-0.0324) and population growth (λ(1994–2008) = 0.9650; 95% CI: 0.9554-0.9746) over time consistent with the decline in calf survival (<1 year old) and a separate reduction in juvenile survival (1 to 3 years old) reflecting cumulative impacts.
Dolphin abundance was estimated in Dusky Sound using photo-identification census and capture-recapture techniques (102 individuals; 95% CI: 100-104) providing no evidence of interchange with Doubtful Sound. A comparative assessment of health status between Doubtful and Dusky Sounds revealed skin lesioning was more severe in Doubtful Sound, particularly among females, and newborn calves appeared to be smaller and were born over a shorter period: factors that may contribute to the low levels of calf survival in Doubtful Sound. The Fiordland bottlenose dolphins were assessed under IUCN Red List regional criteria. The small size of the population (205 individuals; 95% CI: 192-219) combined with the projected rate of decline in stochastic matrix models (average decline: 31.4% over one generation) resulted in a recommended classification of Critically Endangered.