IUCN Red List Assessment
Red List Category
Red List Criteria
Although the data are far from sufficient to make a rigorous quantitative assessment of population trend for N. asiaeorientalis throughout its range, the scale of threats is large enough over enough of the range to suspect and infer a decline of at least 30% over the last three generations (about 50 years, see Taylor et al. 2007). The factor most responsible for such a decline would be incidental mortality in fisheries, but the loss and degradation of habitat (including chemical pollution) and vessel strikes (at least in the Yangtze River system; Turvey et al. submitted) are likely contributing factors as well. As the Scientific Committee of the International Whaling Commission concluded after a review of the species (both N. phocaenoides and N. asiaeorientalis) in 2005 (IWC 2006), “human populations adjacent to the finless porpoise’s habitat are increasing in size and becoming more industrialised so the expectation should be that anthropogenic pressures will continue and intensify.” None of the threats has been seriously addressed in any part of the species’ range, even though threat levels are likely increasing.
Partly because of their small size, phocoenids are exceptionally vulnerable to incidental mortality in gillnets (e.g. Jefferson and Curry 1994). Incidental mortality in fishing gear is either known or presumed to occur throughout the range of Narrow-ridged Finless Porpoises (Reeves et al. 1997, IWC 2006).
There is clear evidence of a declining trend in two major parts of this species’range. In the Inland Sea of Japan, a decline of nearly 70% was estimated over a period of 22 years, from 1976-1978 to 1999-2000 (Kasuya et al. 2002). There is also evidence of a rapid decline in recent decades in the Yangtze River and adjoining lake systems of China (Zhao et al. 2008, Wang 2009); the subspecies there (N. a. asiaeorientalis), which was classified as Endangered in 1996 under the IUCN 1994 Red List Categories and Criteria, is currently being reassessed to determine whether it should be uplisted to Critically Endangered.
Therefore, as is true of the other species of finless porpoise (N. phocaenoides), the Narrow-ridged species qualifies for Vulnerable A2cde, considering that the causes of the suspected/inferred decline in population size--bycatch and mortality from vessel strikes (both interpreted here as “exploitation”), decline in habitat quality, and possibly pollution--have not ceased and are not well understood.