Systems dynamics approach to understanding the impacts of aquaculture closure policies on environmental pressures and fishermen households' incomes in Danjiangkou Reservoir, China

There is a practical demand to explore the trade-offs between environmental conservation and sustainable fishery development due to the increasing implementation of aquaculture closure policies in inland waters. The aim of this paper is to understand the impacts of four closure policy scenarios on aquaculture scale, solid wastes, nutrient yields and household incomes with respect to the Middle Line of the South-to-North Water Diversion Project, Danjiangkou Reservoir, using a systems dynamics approach. The results show that decreasing the aquaculture farmland area is beneficial for reducing the loadings of wastes and nutrients into the water column overall. However, such closures are likely to cause a livelihood dilemma for households depending on aquaculture income from the remaining farmsite operations, as new alternative livelihood options are uncertain. Comparatively, the closure intensity of a policy scenario (scenario 2) in which a 2% occupancy rate is maintained for net-cages in half of the existing aquaculture farmsites provides the optimum outcome by supporting a benefits rebound over a relatively short time period. With further improvements, this policy scenario could lead to lower waste and nutrition loads while preventing an irredeemable decline of fishermen households' livelihoods. Moreover, the long-range trends of aquaculture scales, waste production and nutrition discharges and incomes for each type of household engaged in aquaculture (small, medium and large scales) are highly heterogeneous. Therefore, when implementing the closure intensity prescribed in policy scenario 2, local authorities should help provide type-specific pathways for aquaculture development and diverse alternatives for sustainable livelihoods with considering some win-win strategies.