FEATURE ARTICLE
The Imperiled Giants of the Mekong
Ecologists struggle to understand—and protect—Southeast Asia's large migratory catfish
M. Jake Vander Zanden, Zeb Hogan, Peter Moyle, Bernie May, Ian Baird
Sibling Rivalry
Hatchery fish were a concern because the Thai Department of
Fisheries was pursuing an artificial breeding program for the giant
catfish. Since 1985, thousands of giant catfish that were
artificially reared have been stocked into the Mekong. The site of
their release is almost certainly spawning habitat for their wild
cousins, raising concern about the loss of genetic diversity that
might result from having large numbers of stocked fish overwhelming
the small natural population. Loss of genetic diversity would
further limit the ability of the already-rare catfish to adapt to
changing conditions.
Unfortunately, the program may be doing more harm than good. For
example, in 1999, the largest catch of Mekong giant catfish in
northern Thailand in the last ten years (almost two dozen fish) was
sacrificed to supply eggs and milt for the artificial propagation.
Genetic analysis of the progeny indicated that roughly 95 percent
shared the same two parents. More than 10,000 of these fingerlings
were released in 2001. Although we applaud the Thai government's
desire to rescue the giant catfish from the verge of extinction, the
current method of brood collection and captive breeding seems likely
to erode the genetic diversity remaining in the wild Cambodian
population while also depleting the wild Thai population.
Will the southern population ultimately suffer the same fate as the
one in the north? Perhaps. But we prefer to be more optimistic. Last
year there were several positive steps that may help the Mekong
giant catfish and other threatened freshwater species of the region.
For example, in November the World Conservation Union officially
classified the Mekong giant catfish as critically endangered. This
designation is reserved for Earth's most threatened
species—ones living in only a single location, numbering less
than 50 wild individuals or suffering rapid, dramatic population
decline. Although nobody wants to celebrate that this animal is in
grave danger, the new classification is, in fact, good news for the
giant catfish, because it raises awareness about the necessity for
immediate protection.
Another recent development shows how important it is to get the word
out that this fish is in trouble. Participants in the Mekong
Wetlands Biodiversity Program, an effort of the World Conservation
Union, together with people working for that organization's
Bangkok-based Water and Nature Initiative, recently conducted an
assessment of fish biodiversity, along with a study of the community
fisheries in northern Laos and Thailand. These efforts produced
evidence that the Mekong giant catfish spawns in the area where
rapids were being blasted as part of the Upper Mekong Navigation
Improvement Project, an initiative intended to spur the local
economies. Since publication of these results, plans for blasting
more of the river rapids in Thailand have been postponed. Although
the reasons for that postponement are manifold, one hopes that
icreased awareness of the environmental disruptions the blasting
causes will help to keep the project on hold.
Another recent triumph for the Mekong giant catfish is that one of
us (Hogan) has just completed Samnang and the Giant
Catfish, a children's primer on the ecology and conservation of
aquatic life in the Mekong River. The publisher, a Cambodian
organization called Save Cambodia's Wildlife, is distributing the
book to thousands of youngsters throughout that country. If the big
fish holds on for long enough, perhaps the book will raise awareness
in the next generation of Cambodians about the value of conserving
this and other endangered fish species of the Mekong.
» Post Comment