IUCN Red List Assessment
Red List Category Year Assessed
Critically Endangered Red List Criteria
C2a(i,ii); D Version
Smith, B.D. Reviewer/s
Reeves, R. & Taylor, B.L. (Cetacean Red List Authority) Justification
The best estimate of abundance for the Ayeyarwady population of Irrawaddy dolphins is 59 individuals, based on the December 2003 upstream survey from Mandalay to just above the Taping tributary confluence in Bhamo. Guidelines for considering measurement error (Annex 1: Uncertainty, in IUCN 2001) suggest using plausible lower bounds, rather than best estimates, to determine population size. In the case of dolphins in the Ayeyarwady, this means that it would be appropriate to use 51, the sum of minimum estimates of group size from the December 2003 survey. The threshold of 50 mature individuals for listing a species or subpopulation as CR according to Criterion D (and C2a(i)) refers to the number of individuals known, estimated or inferred to be capable of reproduction. Although the proportion of mature individuals typical for this species is unknown, it is reasonable (and certainly precautionary) to infer that the number of mature individuals in the Ayeyarwady River is less than 50. Therefore, the population qualifies for listing as CR based on Criterion D. The population also qualifies as CR on the basis of Criterion C2a (i, ii) as there are certainly fewer than 250 mature individuals in the population, and a continuing decline in the number of mature individuals is projected or inferred based on continuing threats from gillnet entanglement, electric fishing, and habitat degradation and acoustical disturbance caused by gold mining operations, and the potential threat from bioaccumulation of mercury, and both subcriteria of subcriterion 2a apply (no subpopulation contains more than 50 mature individuals and more than 90% of the total mature individuals are in one subpopulation).
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