Irrawaddy dolphin demography in the Mekong River: an application of mark–resight models

Abstract

Abstract. Riverine Irrawaddy dolphin populations are critically endangered and much uncertainty exists over the population status in the Mekong River of northeast Cambodia and southern Lao People's Democratic Republic (Lao PDR). We conducted 11 surveys over three years to estimate abundance at each survey as well as survival and the probability of individuals becoming unavailable for detection between surveys. We utilized novel mark-resight estimators to account for the detection process in estimating these parameters. Annual survival was 0.977 (0.040 SE) and movement in (0.060) and out (0.018) of an observable state was low. We estimated abundance at 84.5 (95% CI ¼ 77.9-91.2) with little change over our surveys. We also estimated recruitment and population growth rate for the marked, and presumably older, individuals by estimating seniority using a reverse-time model. Seniority was estimated at 0.999 (0.028 SE), recruitment at 0.001 and population growth rate at 0.978. Although the population size appears to be stable, we believe this represents the slow disappearance of a long-lived animal with no recruitment. Along with the isolated nature of the population and reduced population size as compared to historical estimates, we believe this population is in serious threat of extirpation. We believe there may be as few as 7 or 8 animals in Lao PDR and that the species is at risk of extinction there in the short-term. Although recent management actions (e.g., outlawing of explosive fishing and some restriction on the use of gill-nets) have likely been beneficial we believe identifying population goals to work towards, identifying additional management actions to improve recruitment, and designing the survey methods to best estimate the success of these actions is needed.

Likely future extirpation of another Asian river dolphin: The critically endangered population of the Irrawaddy dolphin in the Mekong River is small and declining

“…Ryan et al . () estimated abundance of the Mekong population to be 85 individuals (95% CI = 78–91: including “unmarked” individuals) as of April 2010 using mark‐resight models (McClintock and White , McClintock et al . ).…”

“…This map follows the format of Ryan et al . () so a visual comparison of sighting locations between years can be made ( i.e ., 2003–2007 and 2007–2010). Inset: Lower Mekong Basin.…”

In-water assessments of sea turtles at Glover’s Reef Atoll, Belize

“…This is important for evaluating the status of this Belizean hawksbill turtle population over time because it provides information on long-term prospects for the population and movements in and out of the forereef study area. Mark-resight methods were initially applied to terrestrial mam mals and birds (McClintock et al 2006, Walsh et al 2010, Win gard et al 2011, Franzetti et al 2012) with later applications to fish, cetaceans and seals in the marine realm (Hagen et al 2010, Cordes 2011, Ryan et al 2011, Mansur et al 2012). This is the first known application of mark-resight methods to marine turtles.…”

Assessing Population Trend and Risk of Extinction for Cetaceans Lacking Long- Term Census Baselines

“…Both Sc and Sa can be solved by photo-ID histories [14,29,[46][47][48][49]. An iterated simulation run by re-sampling survival rates (Sc and Sa both and independently) within their lower-upper limits may be introduced to factor in the uncertainties with quantifiable ranges.…”

“…It is my goal to summarize the techniques frequently used to solve the population trend and status/risk assessment in many cetaceans. This summarization could be helpful for the conservation of cetaceans for forming sound conservation actions, especial for the species inhabiting freshwater habitats and coastal waters under intensive anthropogenic threats [10][11][12][13][14][15][16][17] in developing countries.…”