Nutrient loading from a sustainably certified aquaculture operation dwarfs annual nutrient inputs from a large multi-use watershed, Lake Yojoa, Honduras

Net-pen aquaculture is a popular and increasingly prevalent method for producing large quantities of low-fat protein in freshwater ecosystems across the tropics. While there are numerable social and economic advantages associated with aquaculture, there are also challenges related to the environmental sustainability of aquaculture. Chief among these risks is excessive nutrient loading which can drive rapid eutrophication in aquatic ecosystems. In this study, we compare the estimated annual nutrient loads from the six principal tributaries that contribute to Lake Yojoa to the estimated nutrient load of a large net-pen Tilapia operation located in the central region of the lake. We estimated that the Tilapia farm was responsible for ~ 86% of nitrogen (N) and ~95% of the phosphorus (P) annual contributions to Lake Yojoa. This disproportionate nutrient loading of both N and P suggests that this single aquaculture operation, more so than changes in nutrients inputs from the watershed, was responsible for the previously documented deterioration of the Lake Yojoa ecosystem. This study shows the potential for net-pen aquaculture to have disproportionately negative impacts on freshwater ecosystems, even when operations meet all standards for the current state-of-the-art sustainability certifications. We suggest shifts in metrics that could improve the impact of the certification process so that best practices can reduce the impact of net-pen aquaculture on freshwater ecosystems and arrive at the intended goal of long-term environmental sustainability.