Identifying key demographic parameters of a small island–associated population of Indo-Pacific bottlenose dolphins (Reunion, Indian Ocean)

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.

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

“…This high survival rate for adult female is expected for long‐lived mammals, for example in other populations of bottlenose dolphin: 0.96 in Scotland (95% CI 0.94–0.98, Arso Civil et al, ) and 0.94 in New Zealand (95% CI: 0.92–0.95, Currey et al, ). These rates are comparable to other CR studies on small cetaceans: orca (0.98, SE 0.01, Kuningas, Similä, & Hammond, ), and Indo‐Pacific bottlenose dolphin (0.93, 95% CI 0.88–0.96, Dulau, Estrade, & Fayan, ). We did not detect any effect of current reproduction status on survival probability.…”

Photographic Capture-Recapture Analysis Reveals a Large Population of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) With Low Site Fidelity off the North West Cape, Western Australia

“…Within a population, individuals have been observed showing varying levels of residency with individuals typically characterized as residents, migratory (semi-resident) or transient (non-resident). High levels of site fidelity and residency are characteristic of bottlenose dolphins in protected coastal areas with high prey availability and low predation risk (Gowans et al, 2007;Fury and Harrison, 2008;Chabanne et al, 2012;Webster et al, 2014;Brown et al, 2016;Zanardo et al, 2016;Dulau et al, 2017;Passadore et al, 2018). In contrast, low levels of site fidelity is often typical of individuals inhabiting lower productivity areas where prey availability is highly variable in space and time (Gowans et al, 2007;Silva et al, 2008;Edwards et al, 2009;Lafontaine et al, 2017).…”

Using Cost-Effective Surveys From Platforms of Opportunity to Assess Cetacean Occurrence Patterns for Marine Park Management in the Heart of the Coral Triangle

“…Consequently, both species were recorded as bottlenose dolphin (Tursiops spp.). Bottlenose dolphins are known to form stable social groups, sometimes with small resident populations that have a high affiliation to a relatively small area, likely linked to high prey availability and low predation risk (Shirakihara et al, 2002;Dulau et al, 2017;Passadore et al, 2018a;Haughey et al, 2020). In Wakatobi bottlenose dolphins occur wide-spread in the area on a regular basis, thus residency for at least some of these animals is likely.…”