Robust estimates of absolute abundance are vital for management of threatened species, but these have rarely been generated for endangered South Asian river dolphins due to methodological challenges. An estimate of abundance for the Indus River dolphin in 2006 was generated by conducting tandem vessel-based direct counts; conditional likelihood capture-recapture models were then used to correct for missed animals. Group size and sighting conditions were included as covariates, and abundances of the 3 largest subpopulations were estimated as 101 (coefficient of variation, CV = 44.1%) between Chashma and Taunsa barrages, 52 (CV = 14.9%) between Taunsa barrage and Ghazi Ghat, and 1289 (CV = 33.4%) between Guddu and Sukkur barrages. A total of 75.3% of groups were seen by both independent survey teams, and single animals were almost 5 times more likely to be missed than groups of 3 or more. Providing groups can be matched with minimal error, this survey method shows good potential for abundance estimation of dolphins in confined habitat and the shallow rivers of South Asia. Dolphin encounter rates within the Guddu-Sukkur subpopulation (10.35 km −1 ) are the highest reported for any river dolphin. Direct counts conducted over a 35 yr period, suggest that this subpopulation may have been increasing in abundance, probably due to the cessation of hunting and possible immigration from other subpopulations. The future of South Asian river dolphins is intimately tied to water security in the region, and escalating and competing demands for freshwater mean that the long-term future of South Asia's river dolphins is uncertain.
1. Many river dolphin populations are most vulnerable during the low-water season when habitat is limited. Indus River dolphin habitat selection in the dry season was investigated using Generalized Linear Models of dolphin distribution and abundance in relation to physical features of river geomorphology and channel geometry in cross-section.2. Dolphins selected locations in the river with significantly greater mean depth, maximum depth, cross-sectional area, and hydraulic radius, and significantly narrower river width and a lower degree of braiding than areas where dolphins were absent. They were also recorded with higher frequency at river constrictions and at confluences.3. Channel cross-sectional area was the most important factor affecting dolphin presence and abundance, with the area of water below 1 m in depth exerting the greatest influence. Indus dolphins avoided channels with small cross-sectional area (<700 m 2 ), presumably owing to the risk of entrapment and reduced foraging opportunities. 4. Channel geometry had a greater ability to explain dolphin distribution than river geomorphology; however, both analyses indicated similar types of habitat selection. The dolphin-habitat relationships identified in the river geomorphology analysis were scale-dependent, indicating that dolphin distribution is driven by the occurrence of discrete small-scale features, such as confluences and constrictions, as well as by broader-scale habitat complexes.5. There are numerous plans to impound or extract more water from the Indus River system. If low-water season flows are allowed to decrease further, the amount of deeper habitat will decline, there may be insufficient patches of suitable habitat to support the dolphin population through the low-water season, and dolphins may become isolated within deeper river sections, unable or unwilling to traverse through shallows between favourable patches of habitat.
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