Chinensis-type
Studies have been carried out in only a few parts of the chinensis-type’s range, and there is no overall estimate of total population size. Certain subpopulations are thought to be depleted, mostly by habitat destruction/degradation and bycatch in fisheries. Most abundance estimates have been less than a few hundred dolphins, but there appear to be at least 1,200 animals (CVs range from 17-119%) in the Pearl River Estuary of southern China, adjacent to and including Hong Kong and Macau (Jefferson 2000, Jefferson 2005). The Pearl River Estuary population is the only one for this geographic form with quantitative data on population trends, and despite the heavy development in the area and numerous threats, the population has shown no evidence of significant decline in the last 11 years (Jefferson 2005).

Other places where abundance has been estimated are Xiamen, with an estimate of 80 (CV=1.08 - Jefferson and Hung 2004), and eastern Taiwan Strait, which is thought to have a population of only about 99 individuals (CV=52% Wang et al. 2007). Declines have been inferred in both of these areas, based on qualitative environmental information. An estimated 237 (95% CI = 189-318) humpback dolphins inhabit waters around the Leizhou Peninsula, southern China (Zhou et al. 2007). Data on the status of humpback dolphins in Australia are scarce, but by analogy with sympatric (and better-studied) dugongs (Dugong dugon), Corkeron et al. (1997) suggested that they were in decline there. The only statistically defensible estimates for Australian waters are of 34-54 (CVs=13-27%) in Cleveland Bay, Queensland (Parra et al. 2006a), and 119-163 (95% CIs = 81-251) in Moreton Bay, Queensland (Corkeron et al. 1997).

Plumbea-type
As in the case of the chinensis-type, there is no overall estimate of total population size for plumbea-type dolphins. All available subpopulation estimates are in low tens to low hundreds: ~ 450 dolphins (95% CIs = 447-485) in the Algoa Bay region, Eastern Cape coast of South Africa (Karczmarski et al. 1999a), 170-244 in the Richard’s Bay region on the KwaZulu-Natal coast, South Africa (Atkins and Atkins 2002), 105 (95% CIs = 30-151) in Maputo Bay, Mozambique (Guissamulo and Cockcroft 2004), ~ 60 dolphins in Bazaruto Archipelago, Mozambique (Guissamulo and Cockcroft 1997) and 58-65 (95% CIs = 56-102) off Zanzibar (Stensland et al. 2006). Quantitative trend data are not available anywhere in the plumbea-type’s range, but there are indications that some subpopulations have declined in numbers in recent years. For instance, the numbers in the Bazaruto Archipelago decreased from ~ 60 in 1992 (Guissamulo 1993) to probably fewer than 30 in 2003, along with considerable deterioration of the shallow-water habitat across the archipelago (Guissamulo and Karczmarski pers. comm.). Mortality in anti-shark nets off the KwaZulu-Natal coast in the late 1980s was estimated to likely exceed the dolphins’ replacement rate (Cockcroft 1990), but there is no more recent information from that area. Mixing among neighbouring populations is uncertain, although in South Africa none was documented between groups inhabiting locations 800 km apart. Quantitative data are limited, but there are indications that the distribution is discontinuous elsewhere in the plumbea-type’s range, with fragmented and likely discrete populations (e.g.. Karczmarski 2000, Baldwin et al. 2004, A.T. Guissamulo pers. comm., V.G. Cockcroft pers. comm.).

Decreasing