The subpopulation of
Irrawaddy dolphins in the Mahakam River of East Kalimantan, Indonesia, ranges in the mainstem of the river from about 180 km above the mouth to 600 km upstream, seasonally inclusive of Kedang Kepala, Kedang Rantau, Belayan, Kedang Pahu, and Ratah tributaries, as well as Semayang and Melintang lakes (Kreb 1999, 2004). In the early 1980s, dolphins were still commonly reported in Samarinda, about 60km upstream of the coast, but in the early 1990s they rapidly disappeared and are now observed only upstream of about 180 km from the coast. The apparent 120 km range decline represents a loss of about 15% of their historic range (Kreb et al. 2007).
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