Hindcasts and future projections of global inland and coastal nitrogen and phosphorus loads due to finfish aquaculture

A global model is used to calculate feed and nutrient budgets for freshwater and marine omnivorous and carnivorous aquacultural finfish production. The model uses national production data for the period 1970-2010 and the Millennium Ecosystem Assessment scenarios for production and management for 2010-2050. Results indicate that annual nutrient release to the freshwater (1.2 million tonnes of N and 0.1 million tonnes of P in 2010) and marine aquatic environments (0.3 million tonnes of N and 0.05 million tonnes of P) increased less rapidly than fish production, mainly due to improving feed conversion. In the coming five decades, annual nutrient release to freshwater environments may increase to 1.5-2.1 million tonnes of N and 0.1-0.2 million tonnes of P, depending on the production scenario and assumptions on feed conversion and the share of integrated aquacultural production. At present, the global contribution of freshwater aquaculture to nutrient loading of rivers is small. This is the same conclusion reached for the assessment of nutrient export from shellfish aquaculture (Bouwman et al., 2011). However, particularly in Asia, nutrient loading from freshwater fish production and from seaweed and shellfish production is an important factor that should be accounted for when developing models for estimating river nutrient export. Compared to chicken meat and egg production, freshwater aquaculture is a rapidly growing and important cause of the anthropogenic acceleration of the N and P cycles in many parts of the world, and this is especially pronounced in Asia.