Abstract
Photo-identification surveys of Indo-Pacific bottlenose dolphins were conducted from 2009 to 2014 off Reunion Island (55°E33’/21°S07’), in the Indian Ocean. Robust Design models were applied to produce the most reliable estimate of population abundance and survival rate, while accounting for temporary emigration from the survey area (west coast). The sampling scheme consisted of a five-month (June–October) sampling period in each year of the study. The overall population size at Reunion was estimated to be 72 individuals (SE = 6.17, 95%CI = 61–85), based on a random temporary emigration (γ”) of 0.096 and a proportion of 0.70 (SE = 0.03) distinct individuals. The annual survival rate was 0.93 (±0.018 SE, 95%CI = 0.886–0.958) and was constant over time and between sexes. Models considering gender groups indicated different movement patterns between males and females. Males showed null or quasi-null temporary emigration (γ” = γ’ < 0.01), while females showed a random temporary emigration (γ”) of 0.10, suggesting that a small proportion of females was outside the survey area during each primary sampling period. Sex-specific temporary migration patterns were consistent with movement and residency patterns observed in other areas. The Robust Design approach provided an appropriate sampling scheme for deriving island-associated population parameters, while allowing to restrict survey effort both spatially (i.e. west coast only) and temporally (five months per year). Although abundance and survival were stable over the six years, the small population size of fewer than 100 individuals suggested that this population is highly vulnerable. Priority should be given to reducing any potential impact of human activity on the population and its habitat.
Highlights
Achieving reliable estimation of wildlife demographic parameters is of prime importance in ecological research and in most programs involving management and conservation of animal populations
Because the entire range of the species around the island could not be systematically sampled, the Robust Design approach was used to produce the most accurate abundance and survival estimates to date for the Indo-Pacific bottlenose population of Reunion, based on a multilevel sampling of the west coast
The probability of capture was highly variable, both within and across primary sessions, but independent of survey effort, which suggests that sufficient effort was deployed and that the capture probability was mainly conditioned by presence in the survey area
Summary
Achieving reliable estimation of wildlife demographic parameters is of prime importance in ecological research and in most programs involving management and conservation of animal populations. Demographic parameters of Indo-Pacific bottlenose dolphins and preparation of the manuscript was funded by Conseil Regional Reunion (DEE/20151302), http:// www.regionreunion.com
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