Investigating Integrated Multi-Trophic Aquaculture at different spatial sales

Abstract

Integrated Multi-Trophic Aquaculture is being promoted as one of the solutions for the sustainable growth of Aquaculture in the coming years. Open water IMTA endeavours to efficiently use the wastes originating from fin-fish cage farming as a feed source for extractive organisms, alleviating potential environmental impacts. IMTA is a relatively vague term, characterised by a variety of system designs, species combinations and services provided, constituting it complex and multidisciplinary. Regardless the positive suggestions of proof of concept through conceptual desk-based modelling studies, lab-based feeding experiments and in-situ small scale experimental sites. IMTA in the West is not being promoted into formal legislation as a mean for the strategic sustainable growth of aquaculture. Since IMTA is a spatial issue, there is a considerable lack of understanding in terms of planning and setting up and IMTA site In order to achieve this, the aims of this thesis was to create a holistic view on IMTAs main challenges, opportunities and limitation presented in each spatial scale, taking into account the effect of the variability of the natural environment along with the different requirements of the extractive organisms in terms of biology and rearing design. The results of this PhD study suggest that not all regions nor all farm sites are suitable for IMTA and even when a farm is suitable, suitability varies among combination of species chosen. Considering a farm is suitable for IMTA, there are variations in terms of where the IMTA extractive species could be located within the farms waste footprint originating from its biological and stocking density limitations, influencing the bioremediation efficiency of the system. Following the modelling of bioremediation of IMTA, there needs to be a demonstrated in-situ trophic connection between the fed species and extractive species through the use of biological tracers which efficacy varying depending the type of extractive organism targeted. In the case of dissolved inorganic waste, a more suitable approach would be to assess IMTA nutrient budgets at regional waterbody scale (RIMTA). However, each sub-region within the water-body will vary in terms of species produced and biomass of the species produced divided into nutrient source and sinks. Consideration of the hydrodynamic conditions of each subregion could aid on planning activities within a water-body scale to mitigate potential pelagic impacts, offering an integrated ecological management approach.