Evaluating the Functional Trophic Level of the Global Aquaculture Sector

Abstract

Previous studies have characterized the average trophic level of aquatic animals in culture at national, regional or global scales. All of these prior analyses, however, have assumed that the trophic level of an animal in culture is identical to when feeding in the wild. While reasonable for filter feeding organisms, it may poorly represent the diets of farmed aquatic organisms. For these, an estimate of the animal’s functional trophic level is necessary. Building on previously unpublished work, this study pieces together the functional trophic level of all animals in culture globally from 1970 to 2013. The model combines country- and species- specific production data as reported by the Food and Agriculture Organization of the United Nations, with published data on the fraction of a cultured specie’s growth that is feed-based, the composition of that feed, and estimates of the trophic level of marine inputs to aquafeeds throughout the period of analysis. Results not only provide insight into which species in culture deviate most from their natural or wild trophic levels but also allow the examination of the relative dependencies and trajectories of aggregate dependence on terrestrial primary production via crop-based inputs and marine primary production based on fishery-sourced inputs. Results show that as the global aquaculture sector continues to increase in production it is reducing its dependency on marine-derived aquafeed components, which are rapidly being replaced by plant-based alternatives. This leads to the conclusion that the global aquaculture sector has recently seen a decrease in its energy consumption and has the potential to sustainably expand and contribute to global food security.