Using a hodgepodge of local watercraft, the team conducted a 27-day survey of the river's entire length in November and December 2002. In 1998, a tally of 14 separate sightings led to a population estimate of 59 dolphins in the upper part of the river at the time. However, only nine sightings were chalked up during the latest, more extensive survey.
The survey numbers suggest that the population has been reduced to as few as 37 dolphins, said Smith. More surveys would be required to confirm this though, he added.
In addition to a rapid plunge in total dolphin numbers, the species has retreated far into the range it once occupied, he said. British Naturalist John Anderson reported in 1879 that the species could be found a further 500 kilometers (800 miles) downstream from the current limits of its range.
"The decline in their range and the low numbers observed indicate that this population is critically threatened," said Smith.
The primary threat affecting dolphins in the Ayeyarwady river is gill net entanglement. Fishermen increasingly prefer them over traditional throw nets. Fishermen anchor gill nets to the riverbed. The nets indiscriminately trap fish, dolphins, and other animals that swim into them.
Eighty percent of the dolphins killed in Indonesia's Mahakam River are entangled in gill nets, said Danielle Kreb, a conservation biologist with the Conservation Foundation for the Protection of Rare Aquatic Species of Indonesia, in Samarinda, East Kalimantan on the island of Borneo. Kreb estimates that as few as 65 dolphins may remain in the Mahakam River.
Destructive Fishing Practices
A further threat to the Ayeyarwady dolphin population is the illegal practice of electric fishing. Electric fishing uses high voltage to kill everything in range, allowing fishermen to easily gather dead fish from the surface of the water. The practice often occurs clandestinely at night, said Smith.
Probable poisoning from the lucrative and culturally important gold mining industry is another likely reason for the dolphin's demise. "Gold plays a huge role in the ornamentation of pagodas and Buddhist worship in Myanmar," said Smith. Mercury, which is used in chemical processes to extract gold, leaches into the river and may be slowly poisoning the dolphins and other organisms.
"Accidental catch in local fishing gear is by far the largest current threat also facing the Mekong [river] population," said Beasley, who studies Irrawaddy dolphins in that river. "If this threat could be mitigated I have no doubt that the potential survival of the population would increase 100 fold," she said.
Conflict between humans and dolphins arises because of severe poverty in these developing nations, said Beasley. "It's not a simple matter of banning gill nets and other destructive fishing practices local communities depend solely on the fisheries resources for their livelihoods," she said. The answer may lie in persuading local people to implement conservation and management initiatives, she said.
"I believe there would be good support for a site-based conservation program," said Smith, citing the obvious affection the throw net fisherman have for the dolphins. He envisages a conservation scheme that encourages throw-netting with the incentive of lucrative eco-tourism. "A protected area could preserve both the dolphins and the traditional fishing practice of cooperating with the dolphins," he said.
Smith is Asia coordinator for the Cetacean Specialist Group of the IUCN. He plans to submit a proposal that the Ayeyarwady population be listed as critically endangered on the IUCN red list of extinction-prone species.
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