Survival rates for a declining population of bottlenose dolphins in Doubtful Sound, New Zealand: an information theoretic approach to assessing the role of human impacts

Abstract

ABSTRACT1. The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the southern limit of the species' range, exposed to impacts from tourism and habitat modification. Patterns in apparent annual survival were analysed from photographic resightings of naturally marked adults (1990 to 2008) and calves within the first year of life (1994 to 2008) using capture-recapture models.2. The most parsimonious model for adults provided a time-invariant, sex-invariant estimate of survival (j a(1990-2008) 5 0.9374; 95% CI: 0.9170-0.9530), marginally lower than prior estimates for wild bottlenose dolphins.3. The most parsimonious model for calves indicated a significant time-variant decline in survival from an estimate similar to other populations (j c(1994-2001) 5 0.8621; 95% CI: 0.6851-0.9473) to a current estimate that is, to our knowledge, the lowest recorded for free-ranging bottlenose dolphins (j c(2002-2008) 5 0.3750; 95% CI: 0.2080-0.5782).4. Information theoretic evidence ratios suggested that observed patterns in calf survival were 22 times more likely to be explained by a decline coincident with the opening of a second tailrace tunnel for a hydroelectric power station than by a decline in any other year or across multiple years.5. Projections using an age-structured stochastic population model indicated that the current level of calf survival was unsustainable (population decline: 100% of model runs; population extinction: 41.5% of model runs) and was a key factor in the observed population decline in Doubtful Sound.

Accelerating population decline of Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis)

“…Conversely, demographic approaches also provide quantitative predictions of future population trends and extinction risk that can inform precautionary management (Harwood, 2000;Lacy, 1993;Thompson et al, 2000;Fujiwara and Caswell, 2001). Comparative study of rate of decline or risk of extinction between different scenarios of anthropogenic impact using a demographic framework (Moore and Read, 2008;Currey et al, 2009b) can also quantify how uncontrolled environment deterioration may impact long-term survival of threatened populations.…”

Abundance and demography of bottlenose dolphins in Dusky Sound, New Zealand, inferred from dorsal fin photographs

“…Continued photo-iD monitoring of the population will be essential to assess future trends in calf and adult survival. elthough declining survival of calves is most likely driving the population decline in Doubtful Sound (Currey et al 2008), it is important to establish if emigration to other fiords is a contributing factor. Bottlenose dolphins are highly social animals and migrant dolphins could increase their chances of survival by joining an established bottlenose dolphin population (Connor & Norris 1982).…”

“…Coincident with the population decline, the survival of newborn calves decreased from 0.800 before 2000 (Haase & Schneider 2001), to 0.569 (CV = 30%) between and 2007(Currey et al 2007. Preliminary modelling of a long-term data set suaaests that this decline occurred around 2002 Fiordland, New Zealand. and that current levels of calf survival are, to our knowledge, the lowest calf survival rates reported in the literature (Currey et al 2008). The rate of decline in abundance and survival is unsustainable and long-term viability of the population is threatened (Lusseau et al 2006;Currey et al 2007Currey et al , 2008.…”

Predicting the effects of human developments on individual dolphins to understand potential long-term population consequences

“…The studies record the occurrence of each identified dolphin in the study area and whether or not they were accompanied by calves. We focused on the sighting history of calves that were consistently associated with the same female [39], because we anticipated that disturbance was more likely to affect calf survival rather than female pregnancy rate [40,41]. Details of the photo-identification data collection are provided in [26,27,37].…”