The construction of a hydropower plant at Don Sahong channel in Siphandone area will not stop fish from migrating up and down as the fish can use other channels, according to scientists.

The Mekong River splits into several channels in the southern province of Champassak, creating thousands of islands in the Siphandone area.

Scientists tag fish before releasing them so as they can understand how they migrate.

The scientists are tagging and releasing fish as part of a broad research programme to better understand how fish migrate upstream across the Khone falls in the far south of Laos.

They say their research this year demonstrates that in the dry and early wet seasons fish can migrate successfully through channels other than the Hou Sahong, which is proposed as the site of a hydropower project.

The work of project biologists shows that environmental activists are wrong when they claim that the Hou Sahong is the only channel suitable for year round migration across the Khone falls.

According to Dr Peter Hawkins, senior environmental manager of the Don Sahong Hydropower Project, the fish-tagging study is designed to evaluate the performance of channel modifications to improve migration pathways in the Xang Pheuak and Sadam channels.

The fish species targeted for tagging are those that move upstream to cross the Khone Falls. There is an important dry-season migration of small fish like Pa soi from December to March each year, and then a second wave of migrations by bigger fish which are moving upstream to spawn in the early wet season.

???The local fishers know very well that the early wet season upstream migration is their best chance to catch large quantities of fish, and they build elaborate wooden traps in the main channels that cross the falls to intercept these migrants. Unfortunately, many of the fish they catch are just about ready to spawn??? said Dr Hawkins, an expert in environmental management.

Through the month of June, Project staff sat with the trap owners on their l ee and luangkhang traps overnight, so they could select suitable fish just as they were caught. Each fish was then weighed measured and tagged with a barbed yellow plastic marker and released back into the river. Great care was taken in handling each fish so that the tagging process did not affect their behaviour upon release and their re-catchability. The entire tagging operation is over in less than 5 minutes, and at the peak of the run , more than 100 fish were tagged in one night in the Sahong and Xang Pheuak channels.

In order for the programme to provide useful data, tagged fish must be recaptured and tags must be returned. A similar tag study in the Mekong in Cambodia achieved a 15 percent return rate, because fishers knew about the tagging programme and also knew they would receive a reward if they returned a tag.

This study, which started in January 2014, asked fishers who caught tagged fish to return the tag along with information on the location and the date of the catch, for a reward of 20,000 kip, plus the chance to win the 2 million kip prize in a lucky draw that will be held in October this year.

???Recapturing tagged fish shows unequivocally their movements since capture,??? said Dr Hawkins. The evidence we have so far, validates information from local fishers and verifies that fish can indeed migrate through channels other than Hou Sahong, he said.

???The main requirement for success of the fish-tagging research is achieving a high rate of recapture and return of the tags,??? he said. By gauging the proportion of tagged to untagged fish in recaptures, project staff are able to estimate of the number of fish in an area.

By Times Reporters
(Latest Update August 09, 2014)