Abundance estimates of Irrawaddy dolphins in Chilika Lagoon, India, using photo‐identification based mark‐recapture methods

Abstract

[Extract] The conservation status of the Irrawaddy dolphin, Orcaella brevirostris, population in Chilika Lagoon, India (Fig. 1A) has not been assessed using the IUCN Red List criteria, but five other subpopulations of the Irrawaddy dolphin are listed as Critically Endangered (IUCN 2009). These subpopulations are small, isolated and live in human-dominated environments; most subpopulations have fewer than 50 mature individuals (IUCN 2009). A robust estimation of abundance is a key factor in assessing conservation status and to inform future conservation policy for Irrawaddy dolphins in Chilika Lagoon. Estimating abundance to predict trends in small populations of marine mammals is particularly difficult (Aragones et al. 1997, Taylor et al. 2007, Dawson et al. 2008) because (1) detection probability is affected by observer and sea state variables and (2) increases in population size are typically slow due to the low maximum rates of natural increase of cetacean populations. There are no similar constraints on population decline, but in the absence of catastrophes, most declines are also likely to be relatively slow and difficult to detect (Taylor and Gerrodette 1993).