3.1

When considering the status of the entire species Sousa chinensis (including both the chinensis-type and the plumbea-type together), the total population size probably consists of more than 10,000 mature individuals and therefore criterion C for Vulnerable would not apply (although as indicated below, it might apply to each of the two forms when assessed separately). Population reductions can be inferred over much of the species’ range due to heavy fishing pressure (incidental mortality) and habitat loss in coastal and estuarine areas. This inference is supported in some areas by either direct or indirect evidence, including observations of bycatch, interviews with fishermen, and the high and expanding levels of fishing effort with gillnets and other harmful fishing gear. It is possible that the reductions in population size have been large and pervasive enough to cause a net reduction for the entire species of at least 30% over a period of 3 generations (about 60 years; see Taylor et al. 2007) including the past and future. Therefore, the species as a whole comes close to qualifying for Vulnerable based on criterion A4cd, where subcriterion d (actual or potential levels of exploitation) is interpreted to include bycatch. Although the species may not meet any of the criteria for Vulnerable at this time, it is likely to do so in the near future (especially considering the implications of the taxonomic uncertainty described above). Therefore the species is assessed as Near Threatened, and it should be reassessed following taxonomic clarification of the two forms.

Chinensis-type
The available abundance estimates for the chinensis-type humpback dolphin range from a few dozen to over 1,200 for the few small areas of the geographic form’s range that have been studied so far (less than 10%). Although it is possible that the total population numbers in the low tens of thousands, there is no evidence to suggest there are more than that and some reason to suspect the relatively large subpopulation in the Pearl River Estuary, estimated at about 1,200-1,300 individuals, is exceptional. That subpopulation would likely have no more than about 650 mature individuals (estimated % mature = 50% - see Taylor et al. 2007; but also note that there is a direct estimate of 60% mature for that subpopulation – Jefferson 2000, implying as many as 780 mature individuals). Considering the apparently fragmented distribution, the inference of declines in most areas (due to threats as described above and that fact that conservation actions currently are either meager or non-existent in most of the range), and that there could well be fewer than 10,000 mature individuals, the chinensis-type geographic form would qualify as Vulnerable (C2a(i) and possibly also A4cd) if it were assessed separately.

Plumbea-type
All available abundance estimates for plumbea-type humpback dolphins are low (fewer than 500 individuals), and the total number across their range is unlikely to exceed 10,000 individuals. The distribution is discontinuous across most of the range, with probably discrete local subpopulations. Ongoing environmental degradation and loss of key habitats is likely further fragmenting the aggregate population. Exposure to serious environmental stressors throughout their range makes plumbea-type dolphins highly vulnerable, and there are indications of considerable declines in at least some locations. Conservation actions currently are either meager or non-existent throughout the range. It is possible that the decline of plumbea-type animals has been large and pervasive enough throughout their range to cause a net reduction of at least 30% over a period of 3 generations (about 60 years; see Taylor et al. 2007) including the past and future. The plumbea-type geographic form would qualify for Vulnerable (C2a(i) and possibly also A4cd) if it were assessed separately.