The impact of mangroves in small-holder shrimp ponds in south-west Bangladesh on productivity and economic and environmental resilience

Abstract

Aquaculture production in extensive shrimp ponds along mangrove coasts may be influenced by many factors such as pond size, pond management, species diversity of mangroves and aquaculture species used, as well as the position and abundance of mangroves in the ponds. A growing number of studies indicate the potential positive effects of mangrove presence on pond productivity. In this study we aimed to assess the influence of mangrove presence on pond production characteristics as observed in the south-western coastal region of Bangladesh where mangroves grow largely naturally in aquaculture ponds. Using structured interviews we quantified a large number of pond production parameters from mangrove-associated shrimp aquaculture in ponds with a wide range of mangrove coverage (0% - >50%) including total costs, revenues and net profits. The 435 ponds for which data were collected were distributed among 61 villages in four regional clusters. The regions differed significantly in terms of the species present, the total coverage of mangroves, and their position in and around the ponds. Mangrove presence in the ponds correlated strongly with pond productivity and farm profits. Mangrove presence was significantly associated with smaller ponds which had higher input costs and revenue per unit pond area than larger ponds but lower net profitability. Notwithstanding our large sample size, and contrary to our expectations, this study was not able to identify clear profit benefits of the association of mangroves with shrimp ponds. Among various possible explanations, we suggest that, as currently observed in Bangladesh, the presence of mangroves in aquaculture ponds yields little or at most sub-optimal financial benefits. Hence, our results seem to indicate that there is great scope for improving of mangrove-use in shrimp aquaculture. In that, one can expect the largest potential benefit of associating mangroves with shrimp culture in large ponds (“scale benefit”) in which mangroves are presently not being used. The great potential for mangroves to help boost pond productivity and bolster farm economic and environmental resilience clearly remains largely untapped. Our results suggest that further work is needed to help farmers better select appropriate mangrove species, the most suitable locations for planting mangroves and the best percentage of mangrove pond coverage to boost shrimp production. As our cross-sectional study only provides a baseline of mangrove association with shrimp ponds additional, properly controlled experiments following the “Before-after-control-impact (BACI)” design are also needed in order to be able to discern the true causal effects of mangroves on aquaculture production.