FAQ – Fish Migration

Will the Don Sahong project have a fish passage system like the technology being applied at Xayaburi?
Which species occurring around the Khone falls are migratory species?

No. Unlike the artificial concrete fish passage systems being constructed at Xayaburi, the Don Sahong project will improve natural river channels to enhance their existing function as fish passages. After studying the terrain of the Khone Falls area in dry and rainy seasons, the developer has modified several channels and plans to continue further modifications to enhance fish passage.

All fish species in the area migrate upstream/downstream to some degree ??? it???s just a matter of the distance they travel, be it one kilometer or 1,000 kilometers.

How can the developer be sure the modified river channels will be adequate for the numbers and the diverse species that use them?
How can DSHPP expect to provide migration pathways to suit 200 fish species in the region without having detailed knowledge of the ecology of each species?

The seven main channels which cross the falls are each much larger than any fish passage which has been constructed to bypass a dam anywhere, and any one of those channels is large enough to accommodate many species and sizes of fish. Fish which attempt to swim upstream past the falls at present swim into all of the main channels, but at present some fish do not make it through, either because (1) they are caught, especially by fish traps, which are large and numerous, (2) they encounter a waterfall or cascade which is too high or fast for them to pass, or (3) there is insufficient water in the channel at the time. So the main approaches to improve fish passage are to (1) remove fish traps from channels where they are blocking fish migration, (2) flatten waterfalls or cascades or construct channels so that fish can pass around them and (3) enlarge the upstream entrances of channels to increase flow through them, effectively enlarging the size of the channel and attracting more fish into it.

There is no accurate estimate of the number of migrating fish species. What is known is that t all species that migrate through the multiple channels across the Khone Falls are instinctively trying to move to other habitats for spawning, feeding or refuge. The project has now modified three channels, which cross the falls in different places and all now provide alternative pathways for fish species with a range of swimming capabilities. The main channel is Xang Pheuak where ongoing modifications and removal of fish traps will provide better passage than was formerly provided by Sahong Channel. Another channel, Sadam, had no significant natural barriers and the main modification has been to deepen the upstream inlet, thereby increasing the flow and ensuring adequate water for fish migration during the dry season; fish traps, which are barriers to migration, have also been removed. A small side-channel of Phapheng Falls (Sompordan) was recently modified to allow fish passage.

What are the ecologically and economically most important species that migrate?
What if improved passages do not compensate for the damming of Sahong?

All of the fish caught at Khone Falls is eaten or sold by local people, so they are all important, and most fish are migratory to some extent. Most of the common fish are catfishes, carps or loaches, and the importance of individual species varies from year-to-year as they become more or less abundant in response to varying environmental conditions.

Other channels are being modified to improve fish passage success using adaptive management techniques that will ensure that fish can migrate through the area year-round. By taking an adaptive approach to development, any impediments to migration that are detected can be reduced over time.

Many people say it is harder to catch fish than in years past. Why is this?
Isn???t this area full of large fish traps?

The total fish catch may in fact be increasing, but it is being divided among more fishermen, and in particular commercial fishers are increasing their catch and selling to traders to supply distant urban markets. Pressure on the fishery has increased since the 1990s with increasing population, more fishers, more fishing gear and more traders Roads make it easier to sell fish. A 2007 World Bank study found that fishing pressure is the main threat to the trans-boundary fishery between Kratie, Cambodia, and Pakse in Lao PDR. This is especially true between May and July when fish are migrating to breed.

There are several types of large traps, which are considered traditional in this area. But in recent years more traps were built and their average size increased, so in some places they had completely blocked fish migrations. Under the Lao Fisheries Law of 2009 the large traps, which block channels, are illegal, so in May and June of 2016 the responsible Lao agencies removed most of the large traps at Khone Falls.

What is being done to reduce illegal and destructive fishing to enable greater numbers of fish to spawn upstream?
Is the project responsible for poisoning fish?

The Lao Fisheries Law of 2009 made the use of traditional basket-shaped lee traps and luang khang traps illegal because they block fish migrations and in particular target large fish on spawning migrations in the early wet season. With the support of DSHPP, a Don Sahong Fisheries Management Committee has been set up to implement a Don Sahong Fisheries Management Plan. The committee???s top priority is to reduce illegal and destructive fishing. District authorities have removed large traps to make it easier for fish to migrate upstream for breeding. In addition to removing traps, local officials seek to stop the use of explosives, poisons and electro fishing that kill and injure fish and other animals. Local people oppose these methods because they harm fish and benefit only a few greedy fishers.

No. Over the past five years there have been instances where fishermen from Laos and Cambodia have been found using poisons in conservation zones, and some have been arrested. Shops in the area have been selling insecticides and electro fishers. In early 2016, two Cambodians died after eating poisoned fish. None of this is directly related to the project. Apparent increases in destructive fishing in 2016 may be the result of low fish catches generally caused by an extended drought, and pressure from traders to provide commercially valuable fish to export to urban centers distant from Khone Falls. DSHPP actively supports enforcement of the law by the responsible GOL agencies through the Fisheries Management Committee.

Is there a program to monitor fish migration?
What has been learned about fish migration over Khone Falls?

Fisheries monitoring commenced in 2009 and has progressively increased in intensity and sophistication over the past two years. This effort will be sustained throughout the construction phase (2016-2019) as part of an adaptive management strategy that requires monitoring results to assess performance. Thereafter the EIA proposed that monitoring would continue for a further 10 years during the operational phase. This could be extended by the ongoing adaptive management process. As with all instream bioengineering works, the modified channels are being assessed to ensure they are replacing Sahong Channel. DSHPP has committed to carry out additional modifications if needed to ensure successful fish passage. The effectiveness of fish passage is being assessed by comparing the species composition, size-classes and abundance of fish caught downstream of all three channels (Xang Pheuak, Sadam and Sahong) with fish caught upstream of all three channels using appropriate statistical tests. The results will be reviewed by an independent panel and published in an internationally recognized peer-reviewed scientific journal. Trapping of migrating fish and underwater cameras are also used to monitor fish making their way upstream in the dry season.

Prior studies have identified the main migration periods and species and the project???s monitoring has confirmed the same patterns. Fish migrate past the falls for feeding, spawning or refuge. Because water levels are lowest in the dry season, fish migration at that time is the most challenging problem to be addressed by the mitigation measures. DSHPP and critics of the project disagree on whether the mitigation measures are feasible. The Lao Government and the developer believe that because fish attempt to swim through all channels at Khone Falls, removing barriers to their passage will simply enable them to continue on their migrations up alternative channels. Therefore the situation is quite different to that at other dam sites at which artificial concrete fish passages cannot simulate a natural river and do not provide enough water relative to the flow of the river to fully mitigate loss of fish passage via the natural river channel.

What has been done to improve fish passage through the Khone Falls area?
What is involved in mitigation?

The Don Sahong dam will block one of seven main channels. Fish attempt to ascend all of these channels however, waterfalls, rapids and traps may obstruct their way. Sahong Channel was probably one of the best channels for passage but for many years it was obstructed by manmade and natural obstacles. Sadam and Xang Pheuak Channels were also passable over the years. Improvements have now made them more passable. DSHPP has made physical improvements to seven sites on three main channels. Passage will become easier when illegal fishing gear and large traps blocking channels are removed.

In Sadam, Xang Pheuak Noi and Somphordan channels, modifications were made so that more water can flow down them. This is particularly important during the dry season. In Xang Pheuak Noi, Luang Pee Teng, Wai, Nyooi Koong and Luang San, waterfalls were broken down. In Wai, a bypass was created around natural rock obstacles in 2014 and expanded in 2016.

What happens if measures to mitigate fishery impacts are not successful?
How will DSHPP ensure that Sadam has enough water to support fish migration?

DSHPP is very confident the mitigation measures will be successful. DSHPP has set an ambitious target of increasing the success of fish migration across the Khone Falls. This confidence is based on: 1) a detailed understanding of the hydrology and morphology of neighboring natural channels and experience in modifying them to improve fish passage; and, 2) a program to reduce the pressure on fish stocks migrating across the Khone Falls. The sustainability of the fishery resource, particularly its diversity, is currently under threat from overfishing. DSHPP will provide strong support to fishery management agencies to develop and maintain critical migration pathways as conservation zones (capability building) and to better understand fish migration and spawning patterns in the Siphandone region. DSHPP is also actively developing alternative livelihoods and providing training for local people to provide them with alternatives to fishing.

The project is mandated to ensure that future dry season flows in Sadam will either exceed or match existing natural flows. DSHPP has already deepened the upstream inlet of the Sadam channel. If necessary the inlet will be deepened further to ensure the flow will match or exceed a baseline for natural dry season flows.

What design criteria ensure the passages will work for all of them?
Is there evidence to demonstrate these fish passes are working?

The most important design feature is to reduce the gradient at obstructions in other channels to replicate the gradients in Sahong Channel, which was probably the most important fish passage before it was closed in January 2016.

Monitoring results prior to construction show similar dry-season catch rates upstream and downstream in Sahong, Xang Pheuak and Sadam Channels with successful fish passage through each of these channels. Fish could be observed moving through both these channels in the 2015 dry season, and results from the company???s monitoring program to date show similar catch rates downstream and upstream in these channels as in Sahong Channel. In June and July 2016, locally caught fish were in abundance at area markets and prices for many kinds of fish were low, due to the ample supply.

What will DSHPP do if/when the fish that will certainly be attracted to Sahong dam discharge, do not continue upstream on their migration via an alternative channel, and are simply harvested by local fishers?
What is DSHPP doing to investigate whether the new pathways will compensate for the damming of HSH and the loss of that migration path?

Fishing at the outlet of the powerhouse will not be practical or possible for the fishers. This area will be managed by the project to avoid exploitation of any fish accumulation in the area prior to their further upstream movement. Currently fish are attracted to other impassable obstructions (e.g., Phapheng Falls). Local knowledge is that eventually these fish swim back downstream and search for alternative pathways. With monitoring and adaptive management, obstructions will be removed to permit fish passage throughout the period of project operation.

DSHPP will maintain and further develop the fisheries monitoring program, which has been in place since 2009 to test the effectiveness of fish passage.