Probarbus jullieni and Probarbus labeamajor: the management andconservation of two of the largest fish species in the Mekong River insouthern Laos

摘要

1. Probarbus jullieni and Probarbus labeamajor are two of the largest carps in the Mekong River Basin, each reaching a maximum weight of about 70 kg. P. jullieni is listed in Appendix 1 of the Convention on the International Trade in Endangered Species, and both are listed on the IUCN Red List of Threatened Species, the first as "endangered" and the second as "data deficient". 2. Six years of quantitative monitoring of a large- meshed gill net fishery for Probarbus just below the Khone Falls in Khong district, Champasak province, in southern Laos shows that 78% of the overall catch is comprised of Probarbus, with P. jullieni making up 65% of landings. 3. Over the 6-year period catches of Probarbus declined significantly. However, catch-per-unit effort statistics do not indicate that the fishery is in decline, although fishers are convinced that real stock reductions are a large part of the reason for catch declines and decreases in fishing effort. 4. A number of ecological and social factors are affecting the number and quality of gill nets in use, the length of fishing seasons, and gill net efficiency, making it difficult to compare catch-per-unit effort between years. 5. There has been a shift from using large-meshed gill nets for catching Probarbus to targeting smaller species using gill nets with smaller mesh-sizes. This is an example of the "fishing down" of a Mekong fish community, in which large long-lived species are the first to be affected by heavy fishing pressure.