for National Geographic News
March 21, 2007
An Irrawaddy dolphin (right) performs with two pink dolphins at the Oasis Sea World marine park in Chantaburi, Thailand, in 2003. The critically endangered Irrawaddy river dolphin may be in greater danger of extinction than ever, scientists say—and not less, as the government of Cambodia recently announced.
Photograph by Adrees Latif AL/Reuters
Asia's critically endangered Irrawaddy river dolphin may be in greater danger of extinction than ever, scientists say—and not less, as the government of Cambodia recently announced.
According to Touch Seang Tana, chair of Cambodia's Commission for Mekong Dolphin Conservation, there are now about 160 dolphins in the upper Mekong River, up from only 90 when the Cambodian government banned the practice of net fishing last year (see map of Cambodia).
But researchers who study the rare dolphin have expressed deep skepticism that such a dramatic turnaround could have occurred.
They said it would be biologically impossible for the dolphins to rebound so quickly, because their gestation period is 11 months and the animals generally only have one offspring every two years.
There are no dolphins from other areas that could have moved into the upper Mekong River once nets were removed, the researchers added.
"It's impossible that the dolphin population would have increased substantially in only one year," said Isabel Beasley, a Ph.D. candidate at Australia's James Cook University who researched dolphins in the Mekong River from 2001 to 2005.
"The mortality [in recent years] is too high and 95 percent of dolphins in the river already occurred in the areas where the nets were banned."
Dams and Boat Traffic
Two to three meters (seven to ten feet) long, the Irrawaddy river dolphin is similar in appearance to the better known beluga whale. Also known as the Mekong River dolphin, the Irrawaddy is found near coasts and in estuaries in parts of southeast Asia and Australia.
The Irrawaddy's three river populations are some of the most critically endangered dolphins known to exist.
As of April 2005 Irrawaddy dolphins numbered between 127 and 161 in the entire Mekong River, according to Beasley.
Smaller populations are found in Indonesia's Mahakam River and in the Ayeyarwady River in Myanmar (Burma).
Two small lake-bound populations in India and southern Thailand are also known.
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.
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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