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
The Guinness Book of World Records lists the Mekong giant
catfish as Earth's largest freshwater fish. This species
(Pangasianodon gigas), which grows as fast as a bull
and looks a bit like a refrigerator, can measure 3 meters in length
and weigh up to 300 kilograms. Called the "king of fish"
in Cambodia, "buffalo fish" in Thailand and Laos, and
"blubber fish" in Vietnam, this catfish is well known
throughout Southeast Asia. Only the caviar-producing sturgeon,
goliath catfish of the Amazon and a few species of poorly understood
freshwater sting rays rival the Mekong giant catfish in size. In
Europe, the Wels catfish (Silurus glanis) reportedly once
grew to a monstrous 5 meters in length, but today a 2-meter specimen
is considered remarkable.
A century ago, the range of the Mekong giant catfish spanned the
entire length of the river and its tributaries from Vietnam to
southern China. But in the 1930s and '40s, this species began
disappearing, first from the segment of the Mekong that flows
between Thailand and Laos and later upstream, in northern Laos.
During recent times, the status of P. gigas has become
extremely precarious. For example, in Chiang Khong (northern
Thailand) and across the river in the Houay Xai district (Laos), the
1990 haul included just 69 of these fish. The catch from this
stretch of river has fallen considerably since then, and over the
past three years local fishers have not reported a single one.
Noting this absence and similar patterns unfolding elsewhere, we
estimate that the total number of these giant catfish has decreased
by 90 percent or so during the past two decades.
Efforts to save this fish from extinction will hinge on many
factors—including how well biologists understand the migratory
behavior of these animals. Using a variety of approaches, we have
endeavored to provide such knowledge. Here we relate how we became
involved in this effort and where that journey of discovery has
taken us.
The King (of Fish) and I
In 1996, one of us (Hogan) received a Fulbright scholarship for
graduate study at Chiang Mai University in Thailand. During his year
in Chiang Mai, he met another of the authors (Baird, a geographer
and fisheries biologist then working in southern Laos with the Lao
Community Fisheries and Dolphin Protection Project), who suggested
to Hogan that he focus his graduate research on the threats to
various fishes of the Mekong ecosystem.
At the time, this river was gaining recognition as the most
important natural resource in the region, because it provides up to
two million tons of food (both animal and plant) for rural people
each year and because only the Amazon and the Congo can boast a
greater diversity of freshwater species. But the Mekong also faced
new threats. Just a year or so earlier, the Mekong River Commission,
a body created by the four countries bordering the lower Mekong
(Vietnam, Cambodia, Laos and Thailand), coordinated a study to
consider building 12 hydroelectric generating stations. According to
plans, the dams would stand, on average, about 35 meters high. The
slack water behind many of these enormous concrete constructions
would stretch for roughly 100 kilometers upstream, representing, in
total, more than half of the length of the Mekong River along the
span of the slated projects. It was obvious that these dams would
have serious environmental consequences. The Commission found, for
example, that
[a]ll of the proposed dams will block fish migration. This
one impact alone may cause the wholesale decline in the fishery
throughout the lower Mekong River. Blocking migration cuts out a
critical link in the biological chain of migrating species. While it
is possible that some species may find alternative spawning and
rearing areas, there is no data to support such a possibility. It is
not known how far certain species migrate [or] whether stocks can
continue … to function between dams, because stocks and their
migration patterns have not been identified.
The urgent need for even this basic knowledge prompted Hogan to
begin searching for ways to chart fish movements through the Mekong
river system, an effort that would end up engaging all of us in one
way or another.
Hogan began by learning the Thai language. Then, with a small grant
from the Wildlife Conservation Society, he traveled to towns along
the Thai section of the river to record the species for sale at
local fish markets. During this time, he narrowed his focus to the
dozen or so Mekong catfish species in the family Pangasiidae, which
were relatively common, important commercially and interesting
ecologically. What is more, the installation of dams was thought to
pose a particular threat to these fish, given their highly migratory
behavior, adaptation to the natural variation in river flow, and
sensitivity to water quality and temperature.
What he found generally supported what was already known about
Asia's pangasiid catfish: They are seasonal spawners, grouping
together in May, June and July to breed at the beginning of the
rainy season. Catches of Mekong catfish peak at this time, when most
of the fish apparently migrate in schools up the Thai-Lao segment of
the river.
Hogan couldn't describe specific migratory patterns just by
inspecting the offerings in fish markets, but these surveys were
nevertheless valuable. While traveling from town to town, he had a
chance to learn about the fisheries firsthand and to chart the
distribution in space and time of various species of Pangasiidae
from the border between Isan, Thailand, and Champasak Pro-vince,
Laos, in the south to the Golden Triangle region in the north.
He noted, for example, that the Mekong giant catfish and the
slightly less gargantuan "dog eating" catfish
(Pangasius sanitwongsei) appeared in the northern
section of the river between Thailand and Laos in April, May and
June. Smaller species, including the mouse-faced catfish
(Helicophagus waandersii), the snail-eating catfish
(Pangasius conchophilus) and the whiskered catfish
(Pangasius macronema), inhabited the middle stretches
of the river and represented the majority of the catch in this area
between April and June. Surprisingly, one species commonly found in
markets, the river catfish (Pangasius hypophthalmus),
turned out to come from fish-farming operations, not (as Hogan had
first been led to believe) from the river. Wild examples of this
fish are, in fact, very rare in Thai portions of the Mekong. Perhaps
most interesting was the presence of large (meter-long) silver-toned
catfish (Pangasius krempfi) in many fishmongers' stalls.
Why were silver-toned catfish a surprise? A few years before Hogan
arrived in Thailand, Baird had reported that this species could be
found in the South China Sea and also in southern Laos. Baird
surmised that this migratory catfish might be anadromous,
traveling from the marine waters of the South China Sea up the
Mekong through Vietnam and Cambodia and into Laos, where they
presumably spawned. His basic theory, along with Hogan's later
observation of this species in Nong Khai, Thailand (about 1,600
kilometers upstream of the Mekong Delta), provided impetus for a
study of the silver-toned catfish that could better document its
travels. We (Hogan and Baird) began by carefully examining, of all
things, small structures in its ears.
Hogan realized that this curious tactic might reveal migratory
patterns after a chance meeting with Robert Kinzie and Richard
Radtke of the University of Hawaii at Manoa. These investigators
studied the migratory behavior of a different kind of fish, gobies,
using a novel technique—analysis of strontium:calcium ratios
in otoliths ("ear stones"). These small, hard
deposits are found in the heads of all bony fish. Otoliths can be
used to tell how old a specimen is, because they are built up of
distinct layers that are deposited annually. Radtke and Kinzie found
that otoliths can also indicate events that take place as the
animals mature. In particular, the ratio of strontium to calcium in
an otolith records whether the fish had been living in salt water or
fresh water, because strontium concentrations in the ocean are one
to two orders of magnitude greater than in rivers or streams.
Listening to the Stones
With Radtke's offer of help, Hogan and Baird decided to use otoliths
to test whether silver-toned catfish caught far inland had migrated
up from the sea. The base of operation for this study was Hang
Khone, a small village of about 45 families where Baird had been
conducting community-based research on Mekong fisheries since 1991.
This tiny enclave is located in the southernmost province of Laos,
at the edge of Khone Falls, the Mekong's only mainstream waterfall,
and a stone's throw from Cambodia. There, Hogan collected 36
specimens of silver-toned catfish for otolith analysis.
Hogan, Radtke and Baird found that the otoliths contained
significant amounts of strontium—clear evidence that these
fish had lived in salt water. Conversely, the analyses did not turn
up elevated strontium concentrations in related species. These
results helped bring the migratory pattern of this catfish into
clearer focus. Baird had already documented silver-toned catfish
living in the ocean from January through April. And Sophie
Lenormand, a French graduate student working with the Asian Catfish
Project in Vietnam, had determined that adults of this species move
upstream of the estuarine zone in February or March. Higher yet on
the river, in southern Laos, Baird had seen just adults weighing
more than a kilogram or so—and only from May to October. It
thus seems likely that in February and March the silver-toned
catfish move from the sea into the river to spawn, reaching the
Khone Falls, 719 kilometers upstream, in May and June, which is when
the residents of Ban Hang Khone net 98 percent of their yearly haul
of this fish.
This investigation kept Hogan well occupied through his year as a
Fulbright student, but his interest in Mekong catfish did not end
there. Hogan moved back to the United States in 1997 to begin study
for a Ph.D. at the University of California, Davis, under the
direction of another one of us (Moyle). A few years into Hogan's
studies at Davis, Jake Vander Zanden joined Moyle's research group
on a postdoctoral fellowship sponsored by The Nature Conservancy.
Vander Zanden's specialty was stable isotope analysis, specifically
the measurement of carbon and nitrogen isotopes, which can help to
delineate food webs and energy flows in aquatic systems.
So it was quite natural that three of us (Hogan, Moyle and Vander
Zanden) decided to use stable isotopes to fill out the story pieced
together from the earlier otolith study of silver-toned catfish. We
figured that such an analysis could readily tell us whether this big
fish fattens up while at sea. And indeed, our results indicated that
the flesh of this fish has an isotopic signature that reflects
growth in a marine environment, something not seen in other related
species of catfish.
Taken together, our analysis of catch data, strontium in otoliths
and stable isotopes in muscle tissues provided ample evidence that
the silver-toned catfish migrates long distances between fresh and
salt water—the first documented case of anadromy in a Mekong
River species. That is, we had fully confirmed the notion that this
species was a Mekong "salmon," as Baird and Tyson Roberts
of the Smithsonian Tropical Research Institute had dubbed it in
1995. Despite this success, it was clear early on that these
chemical and isotopic methods wouldn't work to investigate the
migratory habits of other species of Mekong catfish, which, as far
as we knew, remain in fresh water throughout their lives. The
inability of these techniques to chart such movements prompted Hogan
to explore an entirely different avenue of investigation, one that
he had earlier rejected as being too expensive and
difficult—following some fish around.
Tag Team
At the time, fisheries biologists in the Mekong region were
suggesting that fish migrate between the Mekong River and Tonle Sap
Lake, the largest inland lake in Southeast Asia, which connects to
the Mekong through a river also named Tonle Sap. In the dry season
(November to February), this remarkable lake covers about 2,500
square kilometers. At the height of the rainy season (August), the
lake area expands fourfold, and the maximum depth increases from 4
meters to 10. Life around the lake, including that of the local
people, is uniquely adapted to this annual cycle. Fish use the
flooded habitat to feed and to grow. The variety of landscapes,
including inundated forests and fields, ephemeral streams and small
satellite lakes, provides habitat for more than 100 kinds of fish
and many more species of birds, reptiles and amphibians.
Every year at the end of the rainy season, the flow of the Tonle Sap
River changes direction from north to south as the water begins to
drain from the flooded forests and plains into the Mekong. With this
outflow come millions of fish. (Residents take advantage this annual
movement by fixing all manner of traps and nets in the lake and
river to snare the migrating fish.) We wanted to determine where
exactly these animals swim: Do they exit the Tonle Sap River and
enter the Mekong? If so, where do they then travel? That is, do they
move upstream or downstream? How far do they go?
Underwater biotelemetry (fitting fish with acoustic or radio
transmitters) seemed a good way to answer these questions.
Biotelemetry systems have often been used to study fish migrations,
to locate spawning and feeding grounds and to describe important
seasonal habitat. But this high-tech strategy had never before been
applied to chart fish migrations within the Mekong River basin,
because most fisheries biologists believed that such tagging would
not be fruitful in a river system so large and complex. Thankfully,
Hogan was able to obtain support from the World Wildlife Fund to try
this approach as well as the more common form of
tagging—attaching plastic markers to fish.
For this study, Hogan and coworkers from the Cambodian Department of
Fisheries collected live fish from a "bagnet" fishery
located in the lower part of the Tonle Sap River near Phnom Penh.
This particular fishery contains about 60 individual nets, each 120
meters long and 25 meters in diameter at the mouth. The first row of
four side-by-side nets is located just outside the city, and the
final phalanx is located some 35 kilometers to the north. This
operation, like many other fisheries in the Tonle Sap River, runs
from October to March, the period when water flows out of the great
lake and into the Mekong and adjacent Bassac River.
Between November 6 and December 1, 2001, Hogan and his Cambodian
colleagues outfitted two Mekong giant catfish and 11 river catfish
with acoustic transmitters and plastic tags labeled "Please
return to the Department of Fisheries." On the evening of
December 9, the hydrophone we were trailing from our survey boat
picked up signals from one of the tagged river catfish. We were
cruising the Mekong, 20 kilometers upstream of its confluence with
the Tonle Sap and Bassac rivers. This acoustic contact indicated
that the fish had moved out of the Tonle Sap River and on up the
Mekong. Although we never actually saw the fish, we were able to
identify it (a 17-kilogram specimen we had tagged on the last day of
November) using the unique pattern of beats programmed into its transmitter.
Two months later, this same fish gobbled up the baited hook of a
local fisher approximately 300 kilometers upstream from Phnom Penh,
which meant that it had traveled nearly 5 kilometers per day.
Fishers have since recaptured several other tagged specimens in this
same area (we learn about such catches promptly, because we provide
a small reward for the return of our tags), suggesting that this
migration route—from the Tonle Sap Lake, down the Tonle Sap
River and on up the Mekong—is typical of river catfish.
Adult river catfish move into deep water areas of the Mekong River
to survive the dry season. They then migrate upstream and spawn with
the onset of the first heavy rains in May and June. Young fish float
downstream with the rising water, eventually finding their way into
inundated areas during the rainy season. These temporary wetlands,
such as the flooded forest of the Tonle Sap Lake, act as rainy
season nurseries for young fish of many other species as well.
Caveat Emptor
While Hogan was tagging fish in the Tonle Sap River, he was becoming
increasingly concerned about the plight of the giant catfish.
Populations were clearly in a nosedive, yet this species continued
to be caught, and there didn't seem to be any readily available
means of regulating the fishery. Then in 1999 he and Nicolaas van
Zalinge (head of the Mekong River Commission's Freshwater Capture
Fisheries Program in Cambodia) hatched an idea: Why not buy any live
specimens caught and release them? In Cambodia, fishermen capture
giant catfish essentially by accident—as "bycatch"
in the local bagnet fishery. These fish sell for very little: about
fifty cents a kilogram. In Thailand, this species was in greater
demand and thus was more expensive. A large fish there could fetch
as much as $4,000. Although purchasing live Mekong giant catfish
from local fishers clearly wasn't a long-term solution, starting a
buy-and-release program seemed better than doing nothing.
The fishers were happy enough with our scheme, because we reimbursed
them for the fish at market price. This approach was attractive to
us, too, for a reason that went beyond just saving the few
individuals that were caught: By purchasing, tagging and releasing
giant catfish, we had a chance—albeit a very small
one—to document any link that might exist between the
specimens found upstream in Thailand and those found downstream in Cambodia.
Hogan figured that it would be straightforward to mark any live
specimens caught with labeled plastic tags and then release the fish
back into the river. Because he had developed contacts in both
Thailand and Cambodia and was thus able to monitor both fisheries,
he'd soon know when one of these marked fish was recaptured. And,
obviously, if a fish tagged in Cambodia showed itself in Thailand,
or vice versa, he'd have concrete evidence that these fish moved
between the two locations (and past the proposed dam sites).
The study of migratory connectivity between these two populations
was not just of academic interest. Indeed, developments taking place
at the time made it seem especially important to understand what the
catfish were doing: The upstream section of the river posed several
threats to this species, the most obvious being the continued
fishing in Chiang Khong, Thailand, where catches of the giant
catfish were shrinking dramatically. Would a decline in the numbers
of giant catfish upstream carry over to the downstream population?
To address such concerns, we needed to know whether the two stocks
intermingled. But suppose no "northern" fish turned up
down south (or vice versa)—would this finding, or rather lack
of finding, mean that these two populations lived in isolation or
merely that all of the tagged fish had been lucky enough to escape
recapture? Knowing that the results of the tagging program might be
ambiguous, Hogan joined the Genomics Variation Laboratory at the
University of California, Davis, where with the help of another one
of the authors (May) he developed genetic markers to study the
Pangasiidae. Using tissue samples from the upstream and downstream
stocks of the giant catfish, Hogan and May hoped to be able to
determine whether these two populations mix.
In 2000, Hogan traveled to northern Thailand to observe the giant
catfish fishery in Chiang Khong. His intent was to buy, tag and
release the giant catfish captured there, as well as to obtain
tissue samples. It was mid-April, the hottest time of the year. So
Hogan found a small, well-shaded guesthouse and checked himself in
for the month. Fishing records showed that most giant catfish were
caught at about this time—and that the season for them was
getting shorter each year. In 1992, for example, the season began
with a catch on April 26 and lasted until June 9. In 1999, the
season started on May 6 and finished just two weeks later. So for a
month, Hogan waited on the patio of his guesthouse, walked down the
street three times a day for a plate of fried rice, read books and
worked on his laptop. But the locals caught none of the big fish.
As it turned out, 1999 was the last year that the catch of giant
catfish in Chiang Khong could be termed a "fishery." After
failing to locate any of these fish in 2000, Hogan returned there in
2001 and again in 2003, yet he never saw a specimen. During his last
trip, Hogan spent a month interviewing local fishers about their
practices and the catch of giant catfish. Everywhere the story was
grim. In one village, locals said that the giant catfish had
disappeared in 1960. In another community, they reported netting the
last one 20 years ago. In Chiang Khong, the giant catfish held out
only through 1999. Taken together, these accounts all pointed to the
same conclusion—that the Mekong giant catfish was all but gone
from northern Thailand.
Fortunately, downstream in Cambodia at least some giant catfish
remained. And the Cambodian Department of Fisheries was eager to
conserve its catfish stocks. So Hogan, with financing from the
University of California and the National Geographic Conservation
Trust, started a program to buy and release the giant catfish that
survived capture, beginning in 2000. In all, he and colleagues in
the Cambodian Department of Fisheries have purchased 21 adult giant
catfish—about 80 percent of the total reported
catch—letting them slip back into the Tonle Sap River. (They
are confident that they hear about most captures of giant catfish,
both because news of these events travels quickly on the river and
because their project has garnered enough publicity that most
fishers know to contact them.) Hogan and his Cambodian counterparts
do the same with 10 other vulnerable species, including the giant
carp (Catlocarpio siamensis), the giant sting ray
(Himantura chaophraya) and the river catfish. In all,
they have bought, tagged, and released approximately 5,000 fish.
But with no giant catfish to examine from the Thai sections of the
Mekong, Hogan had no way to verify whether the tagged
"Cambodian" fish migrate upstream, and he, Moyle and May
had no way to compare genetic makeup between the two populations, if
indeed there still is an upstream population worth talking about.
Despite this setback, we don't consider the investigation a total
washout—far from it. Our genetics work has proved valuable for
other reasons. For one, our results can be used to study the
genetics of other catfish species. And the genetic markers that we
developed also allowed us to examine the diversity of stocks bred in
captivity and to anticipate the effect of release of hatchery-raised
fish into the wild.
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.
Action Plans
Although much remains to be learned about the ecology of the
migratory catfish inhabiting the Mekong, enough good science is now
available to forge a strategy for the sustainable management of
these inland fisheries. This broad survey of the problem isn't the
place to detail prescriptions for better fisheries management, but
we can at least outline what would be involved.
First, maintaining the connectivity between spawning grounds and
nursing areas is absolutely critical, in part because many seasonal
fisheries are based on the catch of migratory fish. It is important
to avoid what happened on the Mun River, the Mekong's largest
tributary in Thailand, where a dam blocked the upstream migration of
many fish, especially catfish, most of which cannot navigate the
ladder constructed to allow them to climb over this obstruction. Not
surprisingly, the local catch of migratory species plummeted after
construction of the dam. The resultant political fallout has been
widespread and long lasting: Fishers protested, and eventually
occupied, the dam site in 2000, and in 2001 the ongoing opposition
prompted the government to consider removing the dam. In the end,
authorities decided to operate the dam at reduced capacity (opening
the massive flood gates for four months of the year), in hopes of
bolstering stocks of migratory fish.
If the Mun River Dam is any indication, planners should be cautious
about proposals for mainstream dams on the Mekong River, recognizing
that no workable design yet exists to mitigate the harm these dams
bring to migratory fish. Dams would also alter the natural variation
in river flow, which is critical to maintain, because the behavior
of migratory fish (and the people who depend on them for a
livelihood) is closely tied to these seasonal changes.
Because the central governments have only limited presence in the
rural areas where the fishing takes place, management of this
natural resource must begin at the local level. But with fish
migrating between Vietnam, Thailand, Laos and Cambodia, action at
the local, or even the national level, is not sufficient. The
fisheries of the Mekong need to be managed as a transboundary
resource. And the authorities drafting the regulations need to be
aware that in a mixed-species fishery such as this, slowly maturing
species are especially vulnerable to over-exploitation—and
thus to extinction. That is, regulations that are able to maintain
the total catch in a multi-species fishery can nonetheless lead to
severe declines among vulnerable groups, most notably large-bodied,
migratory fish.
Ultimately, the preservation of such species must be considered not
only as a matter of fisheries management but also as a conservation
issue. The growing list of threatened migratory fish (P. gigas,
P. sanitwongsei, P. hypophthalmus, P. jullieni, C.
siamensis) demonstrates the need for precautionary actions to
aid their conservation and for greater efforts to assess their status.
One option that acknowledges the shortcomings of typical approaches
to fisheries management would be to pursue an idea recently
championed by Harvard entomologist E. O. Wilson: conservation
concessions. Adopting this tactic on the Mekong River would blend
something similar to what can now be found on land in several places
(including Guyana, Suriname, Bolivia, Peru and the Congo) with the
situation in various marine protected areas. The idea is to purchase
the right to fish commercially in a specified area but not to
exercise it. These "fishing rights" would then become
nonfishing rights: the power to halt large-scale commercial fishing
in certain areas in favor of small-scale subsistence
fishers—and fish. Some people living along the Mekong already
use a similar tactic on a small scale, forbidding fishing in reaches
of the river adjacent to their villages.
This strategy offers a direct method to protect these natural
resources for the long term. If carried out effectively,
conservation concessions have the potential to boost fisheries
production elsewhere, by increasing the spawning stock while at the
same time providing revenue to the governments that issue them, new
jobs for fisheries officials (to enforce regulations within the
concessions) and opportunities for community participation in their
management. Such concessions could either be established with
revenues from ecotourism or with funds from organizations such as
the Asian Development Bank or the Global Environment Facility, which
are both currently involved in large-scale projects in the Mekong
River basin.
Whether or not such conservation concessions are quickly
established, a complete moratorium on the catch of Mekong giant
catfish, including those caught incidentally, is urgently needed.
The remaining population simply cannot support a fishery at this
time. What is more, the ban needs to extend to wild fish caught for
artificial breeding. The Thai Department of Fisheries should breed
existing captive stocks to supply the commercial aquaculture sector.
The captive stocks should also be used to develop a breeding program
that produces greater genetic diversity in the fish that are to be
introduced into the wild. Even if this strategy fails, effective
conservation measures in Cambodia may allow the wild population
there to bounce back, and this "downstream" stock might
then replenish other stretches of the river.
It's obvious that in some spots, notably in China and along some
tributaries, the river ecosystem is deteriorating rapidly. But when
considering the Mekong River as a whole, there is still ample reason
to be optimistic. So far, the main channel of the Mekong river has
not been dammed below China. This waterway remains relatively
unpolluted, and fishers here and on many of the tributaries are
still able to capture phenomenal quantities—some 16 percent of
the world's total freshwater catch. The countries of the lower
Mekong (Thailand, Laos, Cambodia and Vietnam) have shown resolve to
work together for the sustainable development of their shared
aquatic resources. Perhaps they can accomplish something that we
have largely failed to do in North America: develop truly
sustainable fisheries while protecting local biodiversity.
Bibliography
- Hogan, Z. S., and B. P. May. 2002. Twenty-seven new
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