Search

International audience; Environmental sustainability of aquaculture is a complex issue involving effects at local (e.g. benthic deterioration), regional (e.g. eutrophication) and global (e.g. catches for feed production) scales as a consequence of farming operations (e.g. waste emissions) and industrial processes involved in the product value chain. Integrating these effects using a holistic and multi-scale framework is essential to assess the environmental sustainability of innovative production systems such as Integrated Multi-Trophic Aquaculture (IMTA), in which organisms of different trophic levels are co-cultured on the same farm to minimize aquaculture waste. The environmental performances of theoretical production scenarios of red drum (Sciaenops ocellatus) sea cage monoculture and an open-water IMTA co-culturing of red drum and sea cucumber (Holothuria scabra) were assessed with mathematical models at local and global scales. First, the particulate waste bioremediation potential of sea cucumber production was estimated using an individual-based bioenergetic model. Second, environmental impacts of the monoculture and the IMTA systems were estimated and compared using life cycle assessment (LCA), calculated per kg of edible protein and t of product, including uncertainty analysis. Given the current limits to stocking density observed for sea cucumbers, its co-culture in sea cages suspended beneath finfish nets may decrease slightly (by 0.73%) farm net particulate waste load and benthic impact. The monoculture and IMTA showed little difference in impact because of the large difference in production scales of finfish and sea cucumber species. Removing 100% of finfish feces particulate waste requires cultivating sea cucumber at scale similar to that of finfish (1.3 kg of sea cucumber per kg of finfish). Nonetheless, LCA showed trends in IMTA performance: lower eutrophication impact and net primary production use but higher cumulative energy demand and climate change impacts, generating an impact transfer between categories. Intensification of sea cucumber culture could increase local and global environmental benefits, but further research is necessary to design rearing units that can optimize production and/or bioremediation and that can be practically integrated into existing finfish monoculture units. The methodology defined here can be a powerful tool to predict the magnitude of environmental benefits that can be expected from new and complex production systems and to show potential impact transfer between spatial scales. We recommend applying it to other IMTA systems and species associations and including socio-economic criteria to fully assess the sustainability of future seafood production systems.

Robust and accurate prediction of fish farm waste is a first and crucial step in managing the cause–effect chain that leads to local environmental impacts of aquaculture. Since aquatic production is diversifying with new fish species and extending to new areas for which data can be scarce, it is important to develop parsimonious approaches with fewer data requirements and less scientific complexity. We developed the Farm productIon and Nutrient emiSsions (FINS) model, which simulates fish farm operation and estimates fish biomass, feed inputs, and waste emissions from sea cages using simple modeling approaches and a variety of data sources. We applied FINS to red drum (Sciaenops ocellatus) culture in Mayotte by collecting relevant input data (growth, digestibility) from experimental trials. Three explorative farming scenarios—small, medium, and large—were defined from field survey data to examine and compare emissions of a range of potential commercial culture conditions and production scales (23, 299, and 2079 t year−1, respectively). Comparison of the three scenarios showed that waste emissions per ton of fish harvested during routine operations, and thus environmental impacts, were higher for longer culture cycles (medium farm) because of lower feed conversion efficiency. The FINS model is a simple alternative tool to assess and compare environmental impacts of different farming systems and practices for new aquaculture species and regions. It provides important drivers to assess local environmental impacts of fish farms and can therefore facilitate the process of licensing new farming systems for decision-makers.