mekong_cat_featured

The Imperiled giants of the Mekong river.

Largest catfish and largest freshwater fish in the world.Ecologists struggle to understand-and protect-Southeast Asia’s large migratory catfish. 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.

World's largest catfish

Giant catfish, Pangasianodon gigas – Local people – Thailand This Giant Mekong Catfish was caught in Chiang Khong, northern Thailand, on 1 May 2005 by local fishermen. It’s the largest Giant Catfish recorded since 1981. The weight is 292 kg (644lb) CREDIT: (c) WWF /Suthep Kritsanavarin IMAGE No.: 112989

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.

Pangasianodon gigas the Giant Mekong catfish

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.

By  Zeb S. Hogan, Peter B. Moyle, Bernie May, M. Jake Vander Zanden and Ian G. Baird.