Marine finfish and suspended shellfish aquaculture : water quality interactions and the potential for integrated aquaculture

Abstract

The objective of this study was to quantitatively document the culture performance and tissue quality of commercially important deepwater shellfish species (i. e., Pacific oyster, Crassostrea gigas; and Japanese scallop, Patinopecten yessoensis) cultured adjacent to marine finfish aquaculture operations, and to determine (from a production viability and seafood safety perspective) whether integrated finfish-shellfish Multi- Trophic Aquaculture (MTA), or polyculture, is a viable option for the aquaculture industry of temperate regions. Two study sites were employed for this research, one comprising an Atlantic salmon production facility and the other a Pacific salmonf arm. A 2-year assessment program for these sites detailed: (i) oceanographic and physiographicc haracteristics;( ii) organic waste flux, composition and dispersion; (iii) shellfish uptake and contaminant persistence; and (iv) shellfish culture performance. Organic waste flux ranged from 17.11 g/m2/day to 18.35 g/m2/day at the study sites. Phosphorus, calcium, carbon, zinc, cadmium, and strontium were waste constituents that were found at elevated levels at the farm sites with significant declines in concentrations with distance downstream (maximum effect to 100-115 meters). A mass balancee stimation suggested that 85.1% of the organic material (feed) entering the cage was used for fish growth/respiration, 6.8% was lost as settlable solids to the seafloor, and the remaining 8.1% was retained in the water column and a fraction that could affect non-target species (e. g., polyculture candidates) either directly or indirectly. A similar mass balance evaluation for trace metal and chernotherepeutic constituents indicated that 12.9% of the zinc, and an estimated 98.6% of the oxytetracycline contained in feed (during treatment), was released to the water column for potential uptake by co-cultured shellfish. The shellfish monitoring component of this study revealed that trace metal constituents of the feed did become available to the shellfish, although the quantifiable accumulation of trace metals in these non-target species occurred only in close proximity to the cage system and only for the tested scallops (Patinopectin yessoensis). Uptake rates of OTC by shellfish ranged from 0.056 - 0.100 ug/g/day with an associated clearance rate of 0.016 - 0.109 ug/g/day for the respective treatment periods. The comparison of uptake-clearance dynamics suggested asignificant seasonal component to these processes. The physical and biological processes affecting contaminant uptake and clearance rates were identified as important considerations in the management of a proposed integrated-MTA system. A simple Probable Effects Duration (PED) model was developed on the basis of Uptake-Clearance-Persistence plots, illustrating the basis upon which temporal effects of water quality deterioration could be managed in such a system. Shellfish growth was neither impeded nor enhanced as a result of being cultured directly within the influences of a salmon aquaculture facility. An organoleptic test demonstrated that shellfish palatability was not negatively impacted as a consequence of culture proximity to a finfish aquaculture facility. Results of this research suggested that two options are available for developing MTA in coastal temperate waters, i. e., an integrated MTA system and/or an adjacent MTA system. A wide range of MTA social, technical and economic benefits were identified and discussed as a result of this research. It was concluded that the development of a balanced MTA could add measurable environmental benefits to existing aquaculture systemss, setting the stage for future production efficiencies and growth. Given a proper regulatory framework, including seafood (MTA products) and environmental quality surveillanc, the potential water quality impacts on the shellfish component of a finfish-shellfish MTA (identified in this research initiative), and the associated risks over seafood safety, could be effectively managed to support this aquaculture evolution.