Understanding the reproductive parameters of very small or declining populations is of clear importance to conservation. From 1995 to 2011 we recorded calf production (n = 71) and calf survival for 27 breeding females in the bottlenose dolphin (Tursiops truncatus) population in Doubtful Sound, New Zealand; a population with a recent history of declining abundance. Overall, 67% of calves survived their first year, and 40% survived to 3 yr (or are 2 yr old and still alive). Most calves that died in the first year died in their first month (87%). Multiparous mothers (n = 18) showed high variation in calf survival. The most successful six had all but one of their 20 calves (95%) survive to 1 yr. Fourteen of the 20 (70%) survived to 3 yr, and another four are still alive and are 1 or 2 yr old. In contrast, the least successful seven mothers produced a similar number of calves (21), eight of which (38%) survived to 1 yr, and none to 3 yr. Here we describe calving seasonality and calf survival, observed over 16 yr, and show that large variation in reproductive success of individual females is an example of extreme demographic stochasticity in this small, endangered population.

For threatened species or populations, variation in reproductive success among females may be explicitly linked with vulnerability to extinction. Thus, an understanding of factors that may cause variability in reproductive success is important. The population of bottlenose dolphins in Doubtful Sound, New Zealand, has a recent history of rapid population decline and low calf survival rates. A previous study has shown high variability in calf survival among multiparous females. This study addresses the factors that seem most important in explaining variation in calf survival and thus reproductive success among females in this population. Reproductive data were sourced from a long-term photo-identification dataset, which allowed tracking the fate of 49 calves born into the population between 1995 and 2012. General linear mixed models combined with model averaging were used to assess how birth timing, maternal size, age and potential anthropogenic impacts contributed to variation in calf survival. Models show that a female's size and her ability to give birth at an optimum time in the calving season are significant predictors of calf survival to an age of 1 and 3 yr. This is the first study to demonstrate how birth timing and mother size are correlated with female reproductive success in a cetacean species. These results confirm the importance of demographic stochasticity and reproductive heterogeneity in small, threatened marine mammal populations.

Passive acoustic methods are increasingly used to study cetacean habitat use and behaviour. The Timing Porpoise Detector (T-POD; www.chelonia.co.uk) is a self-contained acoustic data logger, which records echolocation by cetaceans. This study used nine T-PODs to document habitat use by bottlenose dolphins in Doubtful Sound, New Zealand, over a 12-month period, collecting data over 76,104 h (of a possible 78,840). T-POD records show that dolphin distribution varied seasonally, with inner fiord sites being used most often in summer and autumn, and outer fiord sites during winter and spring. This seasonal pattern was positively correlated with surface water temperature. Echolocation activity in general and buzzes, which are usually indicative of foraging, were both significantly more common during dawn and/or dusk, suggesting crepuscular foraging. T-POD data suggest that parts of the 'Dolphin Protection Zone', in which boat traffic is restricted, are used frequently while other parts are not, and provide a basis for refining this management tool.

A small population of approximately 68 bottlenose dolphins, Tursiops truncatus, resident in Doubtful Sound, New Zealand, is subject to physiologically challenging conditions, and is exposed to anthropogenic pressure from tourism. A voluntary Code of Management incorporating dolphin protection zones (DPZs), in which tour boat access is limited, was established in 2008. Kernel density estimation (KDE) was used to quantify dolphin habitat use over a 13‐year period in order to describe seasonal variation in habitat use and consistency of habitat use over a decadal period, and to provide quantitative estimates of the extent of overlap between DPZs and core areas (50% volume contour) of habitat use. Habitat use varied seasonally, with the inner fjord area used more frequently in warmer months, and with a shift in use to the outer fjord in colder months. Patterns in habitat use were highly consistent over the 13‐year duration of the study. The spatial overlap between the area of core dolphin habitat and DPZs was low (<18%) overall, and some DPZs were rarely used during colder periods. Consistency in habitat use through time vindicates spatial management, but low overlap between core habitat and current DPZs suggests that an expansion of the DPZ areas would confer greater protection.