Impacts of Irrigation Development on Capture Fisheries in the Rice-Based Farming Systems of Southern Laos

Abstract

"Fish populations inhabiting the rivers, streams, natural wetlands and paddy fields of rice-based farming systems support capture fisheries of major importance to local livelihoods. Water resources development for irrigation has the potential to impact significantly on these fisheries by modifying habitats and their connectivity, as well as patterns of exploitation. We conducted a field survey to establish the impacts of small to medium sized weir and dam irrigation schemes on local fisheries in the rice-based farming systems of southern Laos. The survey was replicated at the irrigation scheme level. Impacted sites were paired with non-impacted controls within the same watershed. Weir schemes were associated with a significant decline in households and per-area catches which as not fully explained by a concomitant change in fishing effort. Dam schemes caused no significant overall decline in catches, but a very significant re-distribution of catches and effort into the newly created reservoirs. In both weir and dam schemes, changes catch were largely explained by changes in fishing effort. No significant impacts on fish species richness were detected. Small-to-medium sized irrigation schemes have only moderate impacts on local fisheries in rice-based farming systems. Net impacts of weirs may be more pronounced than impacts of dams. Rather than being fundamentally degraded as often assumed, fish populations and the fisheries they support can remain productive and diverse within irrigated rice systems. Protecting and enhancing wild fish stocks in such systems is likely to generate social and ecological benefits."