Mekong dam bad news for fish

There are plans to build dams in the Mekong River.
This could be bad news for a type of fish that lives in the river.

Like many other types of fish, the Mekong giant catfish travels great distances to breed in special places in the river.

Dams will get in the way of the fishes’ journeys to these special places.

If they cannot reach them, they will no longer breed properly

Catfish is raised in cages in Chau Doc Town, southern An Giang Province. Damming the main stream of the lower Mekong River will represent a significant new threat to the survival of the Mekong giant catfish, one of the world's largest and rarest freshwater fishes. - VNA/VNS Photo Huy Hung

Catfish is raised in cages in Chau Doc Town, southern An Giang Province. Damming the main stream of the lower Mekong River will represent a significant new threat to the survival of the Mekong giant catfish, one of the world's largest and rarest freshwater fishes. - VNA/VNS Photo Huy Hung

BANGKOK (VNS)— Damming the mainstream of the lower Mekong River will represent a significant new threat to the survival of the Mekong giant catfish, one of the world’s largest and rarest freshwater fishes, according to a new study commissioned by the World Wide Fund for Nature.

The study sheds new light on the status of this elusive species, including data on its numbers, distribution, threats, and measures needed to prevent its disappearance.

While the exact population size is unknown, there could be as few as a couple of hundred adult Mekong giant catfish left.

According to the study, the Xayaburi dam in northern Laos will prove an impassable barrier for the migratory giant catfish — which reach up to three metres in length and weigh as much as 300kg – and risks sending the species to extinction.

“A fish the size of a Mekong giant catfish simply will not be able to swim across a large barrier like a dam to reach its spawning grounds upstream,” said the study’s author and associate research professor at the University of Nevada in the US, Dr Zeb Hogan.

“These river titans need large, uninterrupted stretches of water to migrate, and specific water quality and flow conditions to move through their life cycles of spawning, eating, and breeding.”

Numbers are already in steep decline due to overfishing, habitat destruction, and dams along the Mekong’s tributaries.

In the Mun River, the largest tributary, a dam already blocks the migration of the creature and has isolated the Mun River from the remainder of the Mekong river basin.

The study claims that the controversial Xayaburi dam could disrupt and even block spawning, and increase mortality if the fish pass through dam turbines.

“It is likely the Mekong giant catfish use the stretch of river of the Xayaburi dam as a migration corridor, with adult fish likely passing through this area on their migration from floodplain rearing areas to upstream spawning sites,” Hogan said.

Regional countries agreed at a Mekong River Commission meeting in 2011 to delay a decision on building the Xayaburi dam pending further studies on its environmental impacts.

Puyry, the Finnish firm advising Laos on the US$3.5-billion dam construction, argues that “fish passages” can be built to enable fish to get past the dam’s turbines and swim up and down the river. But this claim has never been successfully put into practice.

“You cannot expect fish ladders to work without understanding your target species, their swimming capabilities,and the water current that will attract these fish toward the pass entrance,” Dr Eric Baran of the World Fish Centre said.

Research is still needed to ensure mitigation efforts will work.”

Mekong giant catfish were once widely distributed through the Mekong river basin, possibly as far as Myanmar and south-western China, and were relatively abundant until the early 1900s.

Their numbers have since plummeted and the species is now limited to the Mekong and its tributaries in Cambodia, Laos and Thailand.

Catch figures also offer sobering evidence of the decline, with numbers dropping from thousands of fish in the late 1880s, to dozens in the 1990s, and only a few in recent times.

Despite laws being in place in Thailand, Laos, and Cambodia to regulate its fishing — with a ban in Thailand and Cambodia — the species is still fished illegally and caught accidentally in fisheries targeting other species.

“Catches should be monitored to ensure that Mekong giant catfish are not being illegally targeted by fishers,” Hogan said.

Incidental catch should also be monitored since it is the only source of information about the distribution, life history, and abundance of this river giant.”

The study identifies key measures to prevent the fish’s disappearance, like immediate efforts to safeguard migratory corridors and critical habitat, and increased international cooperation since the species occurs in an international river and crosses country borders to complete its life cycle.

“The Mekong giant catfish symbolises the ecological integrity of the Mekong River because the species is so vulnerable to fishing pressure and changes in the river environment,” Dr. Lifeng Li, director of the WWF’s Global Freshwater Programme, said. — VNS

GLOSSARY

Damming the mainstream of the lower Mekong River will represent a significant new threat to the survival of the Mekong giant catfish, one of the world’s largest and rarest freshwater fishes, according to a new study commissioned by the World Wide Fund for Nature.

In this case, the mainstream means the main river of many rivers. The Mekong, in its lower areas, which are the areas closer to where it goes into the sea, splits into many different rivers. One of them is larger than the others and it is the mainstream.

If the Worldwide Fund for Nature commissions a new study, it asks someone to do it for them.

The study sheds new light on the status of this elusive species, including data on its numbers, distribution, threats, and measures needed to prevent its disappearance.

Something that is elusive is not seen very often.

A species of plant or animal is a type of plant or animal.

Data is information that is collected.

According to the study, the Xayaburi dam in northern Laos will prove an impassable barrier for the migratory giant catfish — which reach up to three metres in length and weigh as much as 300kg – and risks sending the species to extinction.

The fish cannot pass the barrier. It is therefore impassable.

Fish, birds or animals that are migratory move from one place to another to survive at different times of the year.

An animal or plant that is extinct is gone forever.

“A fish the size of a Mekong giant catfish simply will not be able to swim across a large barrier like a dam to reach its spawning grounds upstream,” said the study’s author and associate research professor at the University of Nevada in the US, Dr Zeb Hogan.

A fish’s spawning grounds is the area where it releases its eggs in order to breed.

“These river titans need large, uninterrupted stretches of water to migrate, and specific water quality and flow conditions to move through their life cycles of spawning, eating, and breeding.”

Titans are living things that are very big and strong.

Numbers are already in steep decline due to overfishing, habitat destruction, and dams along the Mekong’s tributaries.

If there is a decline in the numbers of fish, it means there are fewer than there were beforehand.

The habitat of a plant or animal is a place where things that it needs, such as food and shelter, are available. People talk about habitat destruction when such places no longer have such good conditions.

A tributary is a river that flows into a bigger river.

In the Mun River, the largest tributary, a dam already blocks the migration of the creature and has isolated the Mun River from the remainder of the Mekong river basin.

To be isolated means to be cut off from others.

The remainder of the Mekong River basin means the rest of the Mekong River basin.

A river basin is the entire area from which water drains into a certain river. The basin of the Mekong River covers an area of almost 800000 square kilometres. It includes six countries: China, Myanmar, Laos, Thailand, Cambodia and Viet Nam.

The study claims that the controversial Xayaburi dam could disrupt and even block spawning, and increase mortality if the fish pass through dam turbines.

If something is controversial, people think very strongly about it and with different views.

If something is disrupted, it is interrupted by a problem.

Turbines in a dam are huge round things that the water spins around at great speed in order to create energy, which is captured to make electricity.

“It is likely the Mekong giant catfish use the stretch of river of the Xayaburi dam as a migration corridor, with adult fish likely passing through this area on their migration from floodplain rearing areas to upstream spawning sites,” Hogan said.

A migration corridor is a route taken by creatures that migrate from one place to another.

Rearing areas for fish are places where young fish grow larger. Sometimes they are on flat areas where the rivers flow over when they are in flood. These areas are floodplains.

Regional countries agreed at a Mekong River Commission meeting in 2011 to delay a decision on building the Xayaburi dam pending further studies on its environmental impacts.

If something is regional it is to do with a region. In this case the region is south-east Asia.

If something is pending, a decision about it has not yet been made.

Environment impacts are the ways in which something affects an environment.

Puyry, the Finnish firm advising Laos on the US$3.5-billion dam construction, argues that “fish passages” can be built to enable fish to get past the dam’s turbines and swim up and down the river.

To enable something means to make it possible.

“You cannot expect fish ladders to work without understanding your target species, their swimming capabilities, and the water current that will attract these fish toward the pass entrance,” Dr Eric Baran of the World Fish Centre said.

The fish’s capabilities are what it is able to do. Its swimming capabilities are therefore how well it is able to swim.

Research is still needed to ensure mitigation efforts will work.”

Research is work done to find out more about something.

Mitigation efforts, in this case, means things that will make it easier for the fish. To ensure them, means to make sure they happen.

Mekong giant catfish were once widely distributed through the Mekong river basin, possibly as far as Myanmar and south-western China, and were relatively abundant until the early 1900s.

When wild animals, or plants are distributed over a certain area, it means they may be found living naturally in that area.

If something is relatively abundant, it means there are many of them. However, it is only many compared with other catfish, or other fish in the Mekong, not many compared with other types of fish of which there are many.

Their numbers have since plummeted and the species is now limited to the Mekong and its tributaries in Cambodia, Laos and Thailand.

If the numbers of something plummet they drop down very suddenly and to a very small number.

Catch figures also offer sobering evidence of the decline, with numbers dropping from thousands of fish in the late 1880s, to dozens in the 1990s, and only a few in recent times.

Evidence means proof. Sobering evidence is proof of something that may give someone a bit of a shock.

Despite laws being in place in Thailand, Laos, and Cambodia to regulate its fishing — with a ban in Thailand and Cambodia — the species is still fished illegally and caught accidentally in fisheries targeting other species.

To regulate something means to have more laws around it.

“Catches should be monitored to ensure that Mekong giant catfish are not being illegally targeted by fishers,” Hogan said.

If something is monitored it is watched carefully.

Incidental catch should also be monitored since it is the only source of information about the distribution, life history, and abundance of this river giant.”

Incidental catches involving catfish happen when fishermen fish hoping to catch other types of fish but also catch some catfish.

The study identifies key measures to prevent the fish’s disappearance, like immediate efforts to safeguard migratory corridors and critical habitat, and increased international cooperation since the species occurs in an international river and crosses country borders to complete its life cycle.

The life cycle of a creature is its journey from one form to another between being born, or hatching from an egg, to producing babies to death.

“The Mekong giant catfish symbolises the ecological integrity of the Mekong River because the species is so vulnerable to fishing pressure and changes in the river environment,” Dr. Lifeng Li, director of the WWF’s Global Freshwater Programme, said.

By having ecological integrity, the Mekong River can be trusted as being a balanced environment where plants and creatures have a chance at surviving.

If something is vulnerable it can easily be harmed.

WORKSHEET

Match the two parts of these sentences:

1. The Mekong giant catfish ….

2. Puyry is a ….

3. The University of Nevada is …

4. Part of Myanmar falls into …

5. “Fish passages” make it possible for …

a. …. a firm from Finland.

b. … now lives only in the tributaries of the Mekong River in Cambodia, Laos and Thailand;

c. … fish to get past turbines and swim up and down the river.

d. … in the United States.

e. … the Mekong River Basin.

ANSWERS:

1-b; 2-a; 3-d; 4 -e; 5-c.

Sponsored links
comments powered by Disqus