Passive acoustic monitoring of habitat use by bottlenose dolphins in Doubtful Sound

In the context of testing the appropriateness of current conservation management, this study used nine moored acoustic monitoring devices (T-PODs) to monitor habitat use by bottlenose dolphins in Doubtful Sound, New Zealand, and identify current critical habitats. Static acoustic monitoring offers several advantages over visual surveys, including detection of submerged animals, non-invasiveness, long-term 24 hour coverage, lower expense and reduced dependence on calm weather. T-PODs are relatively new devices however, and required investigation of their performance and limitations. T-POD frequency settings were found to significantly influence detection ability. The A/B filter settings of 50/30, 70/30 and 90/30 (kHz) were found most effective. The maximum range of bottlenose dolphin detection was measured at 1313m. Dolphin detection rate and probability both declined with distance from T-POD. The conservative nature of T-PODs was highlighted as only 47% of bottlenose dolphin groups were detected when within 500m of T-POD. The effective detection radius (EDR: range at which all groups can be assumed to be detected) was calculated to be 266m (95% CI; 222m-317m). Detailed inspection of T-POD data files allowed identification of foraging echolocation trains, which were used to define parameters to identify ‘buzzes’; a unique echolocation signal used when capturing prey. Click trains with interclick-intervals between 18-2 ms and >20clicks were defined as foraging. These foraging parameters, when tested on a new sample of T-POD data, positively identified 92% of visually identified foraging trains. Nine separate T-POD sites within Doubtful Sound were acoustically monitored for twelve months from 1st April 2009. Foraging behaviour was not focused in particular sites, suggesting opportunistic foraging strategies are employed by the population. Foraging and encounter rates, among all T-POD sites, were significantly higher during diel phases dusk and dawn, compared to day and night. T-POD data showed that dolphin use of the fiord varies seasonally with inner fiord sites being used most in summer and autumn, and outer fiord sites in winter and spring. Seasonal dolphin presence was positively correlated with surface water temperature. Seasonal trends from this study were consistent with previous studies, highlighting Crooked Arm (site D), Hall Arm (site B) and ‘The Crossing’ (site E) as most critical. Habitat use data gained in this study suggested that the current Dolphin Protection Zones, in which boat activity is voluntarily limited, do not provide adequate protection for the population. Seasonal variation in the scope of the DPZ, additional no boat zones and extensions to current DPZs are proposed for re-assessed critical areas. These modifications are seen as necessary for effective conservation management, whilst being practical for Doubtful Sound stakeholders