Mark-resight abundance and survival estimation of Indo-Pacific bottlenose dolphins, Tursiops aduncus, in the Swatch-of-No-Ground, Bangladesh



A mark-resight analysis under Pollock's robust design was applied to Indo-Pacific bottlenose dolphins Tursiops aduncus in the Swatch-of-No-Ground (SoNG) submarine canyon, Bangladesh, during the winter seasons of 2005–2009. Information from sightings of photo-identified individuals (1,144) and unmarked individuals generated abundance estimates of 1,701 (95% confidence interval [CI]= 1,533–1,888), 1,927 (95% CI = 1,851–2,006), 2,150 (95% CI = 1,906–2,425), and 2,239 (95% CI = 1,985–2,524) individuals for seasons 1–4, respectively. This makes the population among the largest assessed of the species. Overall apparent survival was estimated as 0.958 (95% CI = 0.802–0.992). Interseasonal probabilities of transitioning to an unobservable state were estimated as 0.045, 0.363, and 0.300 for years 1–2, 2–3, and 3–4, respectively, and the overall probability of remaining in an unobservable state was 0.688. These probabilities, together with an apparent increase in abundance during the study period, indicate that the identified dolphins are part of a larger superpopulation moving throughout a more extensive geographic area. Of the photo-identified dolphins, 28.2% exhibited injuries related to entanglements with fishing gear. This implies a strong potential for fatal interactions that could jeopardize the conservation status of the population, which otherwise appears favorable.