Dam-building, boat traffic, and pollution have negatively impacted dolphin populations over the last several decades.
"The Mekong dolphin population [has been] declining by 4.8 percent per year, with most newborns dying from unknown causes within one to two weeks of birth," Beasley said.
"The population will not increase until calf survival improves."
"Accidental catch in gill nets is the other major threat," Beasley added.
(Read related story: "Gold Mining, Nets Imperil Rare Dolphin, Groups Say" [March 4, 2003].)
No Gill Nets
Net fishing was banned last year in Cambodia's upper Mekong River, where local people were encouraged to grow crops or work in the burgeoning tourism industry instead of fishing.
The absence of gill nets strung in the river has resulted in the sudden jump in dolphin numbers, Cambodian officials maintain.
"We should have about 20 new babies born every year if the current trend continues," Tana, the conservation commission chair, told Reuters news service earlier this month.
Zeb Hogan, who studies large river fish in Asia, visited the area last month and confirmed that fishers were no longer using gill nets.
"It was the first time that I had seen that in Cambodia," said Hogan, a researcher with the University of Nevada at Reno and a National Geographic Emerging Explorer based in Phnom Penh, Cambodia.
(National Geographic News is a division of the National Geographic Society.)
In response to researchers' skepticism about his government's latest population estimates, Tana said his figures were accurate.
"Even [though] the deaths of new offspring [were] found to have increased from about ten in 2000-2001 to more than 20 in 2005-2006, the dolphin population was slightly increased," he said via email.
"And according to my observations, [the population] was about a hundred and sixty in February 2007."
Tana also pointed out that obtaining accurate population numbers can be very difficult.
The Mekong's frequently murky waters make techniques such as photo censuses impossible, he said, and the dolphins' tendency to break off into small, mobile groups can make "confusion and mistakes unavoidable."
Ian Baird of the University of British Columbia in Vancouver, Canada, has studied Mekong River dolphins since the early 1990s.
He said he "appreciates the efforts that people are making to try to help" the dolphin population, but he said major rebounds are not going to occur in just one year.
"While we would all love to report that the dolphins are rebounding, I think that it is highly likely that the opposite is actually occurring," he said. "This may well be a case of wishful thinking."
Baird said plans to build large dams on the Mekong River pose a serious threat to the future of the dolphins and fisheries.
"One large dam could lead to the end of the Mekong River dolphin," he said.
Beasley, of James Cook University, said "it is extremely detrimental to dolphin conservation efforts to indicate that the population is making a comeback when it probably isn't."
She is also concerned that encouraging local communities to diversify into ecotourism activities such as dolphin-watching may place even more harm on this critically endangered population.
"As far as I know, no studies have yet been conducted on the effect that dolphin-watching is having on the population," she said, "though I suspect that the effects are quite significant as a result of high levels of boat activity."
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