Indo-Pacific Humpback Dolphins: A Demographic Perspective of a Threatened Species

Abstract

Indo-Pacific humpback dolphins inhabit shallow coastal waters within the tropics and subtropics of the Indian and Western Pacific Oceans. Their taxonomy remains unresolved, between a single widespread and highly variable species, two species, and three species being currently proposed. Their inshore distribution renders them highly susceptible to the adverse effects of many human activities; for most of the known remaining populations their continuous survival is a subject of major conservation concern. In this chapter, we describe the use of demographic analysis to quantify population trend and, more informatively, predict the risk (probabilities) of extinction. The results of demographic analyses provide valuable means of assessing conservation status. Using the population of humpback dolphins from the Pearl River Estuary as an example, we show the power of demographic analyses, predicting a significant population decline before it is directly documented by other standard techniques. Comparing our findings with known, albeit limited data from southeast Africa, and considering the current ambiguity of the taxonomic classification adopted by IUCN, we question the current listing of humpback dolphins under the IUCN Red List of Threatened Species. We urge that their conservation status classification be reconsidered as it likely understates, perhaps severely, the threats faced by many fragmented populations off Southeast Asia and the western Indian Ocean.