Correction: Use of the Robust Design to Estimate Seasonal Abundance and Demographic Parameters of a Coastal Bottlenose Dolphin (Tursiops aduncus) Population

Abstract

As delphinid populations become increasingly exposed to human activities we rely on our capacity to produce accurate abundance estimates upon which to base management decisions. This study applied mark-recapture methods following the Robust Design to estimate abundance, demographic parameters, and temporary emigration rates of an Indo-Pacific bottlenose dolphin (Tursiops aduncus) population off Bunbury, Western Australia. Boat-based photo-identification surveys were conducted year-round over three consecutive years along pre-determined transect lines to create a consistent sampling effort throughout the study period and area. The best fitting capture-recapture model showed a population with a seasonal Markovian temporary emigration with time varying survival and capture probabilities. Abundance estimates were seasonally dependent with consistently lower numbers obtained during winter and higher during summer and autumn across the three-year study period. Specifically, abundance estimates for all adults and juveniles (combined) varied from a low of 63 (95% CI 59 to 73) in winter of 2007 to a high of 139 (95% CI 134 to148) in autumn of 2009. Temporary emigration rates (c') for animals absent in the previous period ranged from 0.34 to 0.97 (mean = 0.54; 6SE 0.11) with a peak during spring. Temporary emigration rates for animals present during the previous period (c'') were lower, ranging from 0.00 to 0.29, with a mean of 0.16 (6 SE 0.04). This model yielded a mean apparent survival estimate for juveniles and adults (combined) of 0.95 (6 SE 0.02) and a capture probability from 0.07 to 0.51 with a mean of 0.30 (6 SE 0.04). This study demonstrates the importance of incorporating temporary emigration to accurately estimate abundance of coastal delphinids. Temporary emigration rates were high in this study, despite the large area surveyed, indicating the challenges of sampling highly mobile animals which range over large spatial areas.

Dolphin Prey Availability and Calorific Value in an Estuarine and Coastal Environment

“…However, the nutritional value of prey may be a more critical component of prey value and therefore an important component of any investigation into foraging ecology. In this study, a concomitant increase in abundance of prey was predicted to coincide with the increase in abundance of bottlenose dolphins during summer months off Bunbury, Western Australia (Smith et al, 2013;Sprogis et al, 2016a). The results of prey sampling indicated a higher abundance of prey in the summer seasons, however, the overall biomass and energy density of prey documented were higher in the winters, when fewer dolphins were present, but a time when dolphin mothers and calves remain in the area.…”

“…The population of bottlenose dolphins in the Bunbury region, approximately 180 km south of Perth, Western Australia, utilizes the Leschenault Estuary (Estuary), Koombana Bay (Bay), and the near shore coastal waters (Ocean) (Figure 1; Smith et al, 2013;Sprogis et al, 2016a).…”

“…Sampling days were spread across the sampling season. The summer season extended from January to mid-March corresponding to the period when dolphins are most abundant in the area, while the winter season extended from June through September when fewer dolphins are present (Smith et al, 2013;Sprogis et al, 2016a).…”

“…Since the abundance of dolphins is lower during winters (Smith et al, 2013;Sprogis et al, 2016a), it was hypothesized that prey quantity would be also be lower, but that prey quality would be relatively higher to support the mothers and calves that remain in local waters throughout the winter (Smith et al, 2016), as the energetic cost of lactation and growth is high (Malinowski and Herzing, 2015). As hypothesized, the highest energy contents of fish were generally found in the winter: the highest KJ in traps and gillnets were found in the winter season; while the energy content in the seine net was similar in summer and winter.…”

“…The abundance of dolphins fluctuates seasonally, with approximately double the population size in the summer vs. the winter months (Smith et al, 2013;Sprogis et al, 2016a). The seasonal high in abundance coincides with the peak in the breeding and calving season, in late summer/early autumn (Smith et al, 2016).…”