Title
Detecting the unseen through application of a robust mark–resight design for estimating humpback dolphin demographics in Bangladesh
Author(s)
Mansur, R.W.;Smith, B.D.
Published
2015
Publisher
Cambodian Journal of Natural History
Abstract
Estimating the demographic parameters of highly mobile wildlife is particularly challenging when detection is imperfect and only an unknown portion of the geographical range of a super-population can be sampled. Addressing this challenge has vital implications for protecting species whose distribution and conservation risk are poorly known. A mark–resight analysis under a robust design was applied to Indo-Pacific humpback dolphins Sousa chinensis, in open estuarine waters off shore of the Sundarbans mangrove forest, Bangladesh. During three winter seasons in 2010–2013, 88 humpback dolphin sightings were made along more than 5,000 km of track line. Almost 43,000 dorsal fi n photographs resulted in the identification of 468 individuals, with an average re-sighting rate of 0.85, and abundance estimates of 132, 131 and 635 for the three winter seasons, respectively. The considerable increase in the abundance estimate during the third season can be explained by the large number of new dolphins identified for the first time during the third year. This includes a single group of 205 photo-identifi ed individuals that is by far the largest group ever recorded of the species. The increase is also reflected in a 55% probability estimated using a robust design over the three winter seasons of an individual remaining in an unobservable state in the next survey when in an unobservable state in the previous survey. The results of this study indicate that the coastal waters in our survey area support a portion of a larger superpopulation that occupies a more extensive area in both Bangladesh and India.

Access Full Text

A full-text copy of this article may be available. Please email the WCS Library to request.



Back

PUB15584