PESUT MAHAKAM

This is a freshwater subpopulation of Orcaella brevirostris Owen in Gray, 1866, found in the Mahakam River, East Kalimantan, Indonesia. No genetic analyses have been carried out to assess the affinities of this subpopulation to other nearby subpopulations of the species. However, extensive surveys of the lower reaches of the Mahakam River and adjoining coastal waters, along with fisherman interviews, indicate that freshwater dolphins do not move farther downstream than about 90 km from the coast, and marine dolphins do not move farther upstream than about 10 km from the coast, and then only at high tide. The Mahakam dolphins also show strong fidelity to specific confluences and there is no evidence to suggest that they make long-distance movements (Kreb et al. 2007). Therefore, it is reasonable to consider this an isolated freshwater subpopulation.

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