SBR- Content.pmd - INBO

7 - FisheriesEven though the total yield may in fact be increasing, there are indications of selective over-fishing. 104Species that need more than one year to reproduce are declining quickest. 105 The LMB populationis growing at an average of 1.45 percent per annum, 106 though with the growth rate in Cambodia at2.6 percent and Lao PDR at 2.8 percent, 107 there will be greater pressure on natural aquatic resourcesin years to come.2.7.5 Other impactsRiver modificationRiver modification includes construction of navigation channels, locks and weirs, which alter rivertopography and water flow patterns. Some of the likely impacts on the fishery are typified byinvestigations conducted for the Mekong River Channel Improvement Project (MKRCIP), designedto increase the navigability for shipping in the upper Mekong River, 360 km from the Chineseborder down to Ban Houei Sai in Lao PDR. 108 The MKRCIP plans the removal of assorted sand bars(mid-channel bars, bank-attached bars, tributary-mouth bars, and bedrock bars).Roberts 109 considers that the blasting of rapids, rock bars and islands, the dredging of substrate,construction of ports, and other development, may lead to fish kills in the project zone, but alsothere will be significant international “trans-boundary” implications.DeforestationThere is currently no information available on the impactof deforestation in the highlands on the fisheriesresources of the Mekong Basin. The serious implicationsof removal or conversion of flooded forest on thefloodplains is covered in Section 2.7.3, and within theLMB, the deep pools, which are important dry seasonfish habitats, would be in danger from excessive siltdeposition resulting from increased erosion caused bydeforestation.In general terms, deforestation is associated with increasederosion and instantaneous run-off to streams and rivers.Erosion increases sedimentation, turbidity, totalsuspended solids, and conductivity. High suspended solidloads irritate fish gills and smother fish eggs, preventingoxygen exchange. Increased run-off to rivers alsoincreases nutrient concentrations and nutrient loads inrivers. Deforestation alters water temperature anddecreases the leaf litter available to the aquatic food chain.All the above adversely affect aquatic flora and fauna. 110Conversion of flooded forest to agriculturalland is a threat to fish productionDestructive fishing practicesDestructive fishing practices include the use of fine meshed nets, fishing during spawning seasonsand in dry season refuge areas, and using electricity, poisons and explosives. Fishers use explosives indeep pools and channels in northeast Cambodia during the dry season. 111 This illegal fishing methoddestroys spawning populations, which are sheltering in the deep pools until the next flood pulse. 112117