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dam-l LS: Letter to Bangkok Post about Fish ladders

Bangkok Post, May 29, 2000

Not all fish ladders serve the purpose
While visiting Thailand recently, I was interested to follow the protests at 
Pak Moon dam reported in the Bangkok Post concerning the blockage of fish 
migrations. It seems the ineffective fish ladder has contributed to the 
current level of confrontation between the villagers and officials.

>From the pictures we have since seen of the fish ladder, we see it has been 
designed after fish ladders in North America for strong swimming salmon. 
Unfortunately, the failure of such a fish ladder for species other than 
salmon is not unique to Thailand and similar experiences have been reported 
in other tropical regions (eg. northern Australia, central Africa, South 
America and other parts of Southeast Asia). Fish in tropical rivers often 
have a relatively poor swimming ability and follow different migration 
strategies to salmon.

There have been some important recent advances in fish ladder design for 
tropical rivers and with careful planning, successful passage facilities for 
dams such as Pak Moon can be built. Fish communities in tropical Australia 
have similar features to those in Thailand in terms of their great 
abundance, high species diversity and variation in size and life cycles. New 
fish ladders based on those from North America, but adapted over the last 
decade for tropical fish, have allowed more successful migrations.
Some allow several thousand tropical fish to pass the dam per day. The fish 
ladders now play an important role in allowing fish to reach their spawning 
grounds and for dispersal of young fish. They work because of very slow 
water velocities, a gentle slope and an ability to operate over a range of 
river levels during both the dry season and the wet season. In short, they 
do not require fish to jump.

Sometimes old, ineffective fish ladders can be modified to a more successful 
design without the need for an entirely new structure. However, for fish 
ladders to be effective they also need to incorporate a broader fish 
migration plan with an operational protocol for the dam and its water 
resources.

Opening the sluice gates at Pak Moon dam may or may not allow a greater 
level of fish migration, but this contributes little to resolving similar 
issues at other dams in Thailand.

Clearly, there should be greater emphasis on developing plans to maintain 
the passage of migratory fish at new dams, as well as expanding research 
activities on freshwater fish in Thailand.
The dam is very likely to have a much greater impact on fish than simply 
blocking their migration, but a working fishway would be a first step in 
restoring the ecology of these fish populations and in resolving this 
dispute.

Ivor Stuart and 
Martin Mallen-Cooper 
Fish ladder Biologists 
Australia





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Aviva Imhof
South-East Asia Campaigner
International Rivers Network
1847 Berkeley Way, Berkeley CA 94703 USA
Tel: + 1 510 848 1155 (ext. 312), Fax: + 1 510 848 1008
Email: aviva@irn.org, Web: http://www.irn.org
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