Science Advisory Report 2008/001
Potential Technologies for Closed-containment Saltwater Salmon Aquaculture
- Closed-containment is a term used to describe a range of technologies that attempt to restrict and control interactions between farmed fish and the external aquatic environment with the goal of minimizing impacts and creating greater control over factors in aquaculture production.
- In principle, technologies are available to restrict and control interactions but they must be evaluated in relation to their costs in terms of environmental impact mitigation, capital investment and operational parameters, all of which may be site specific.
- A review of over 40 closed-containment systems from around the world found that none was producing exclusively adult Atlantic salmon and that many previous attempts to do so had failed. Reasons for failure were numerous and were often interrelated. These reasons included but were not limited to mechanical breakdown, poor fish performance, management failure, declines in market price and inadequate financing.
- Five types of production systems were described and examined: (a) conventional net pen; (b) floating, closed-confinement systems with rigid walls; (c) floating, closed-confinement systems with flexible walls; (d) land-based flow-through system; and, (e) a land-based reuse system.
- The engineering challenges associated with various designs of floating closed-containment systems were modeled. Those constructed of rigid material and anchored to the bottom represent a particular challenge in terms of the tidal currents and wave heights that are typical of exposed areas, which may mean that site selection for those types of structures may be limited by these two oceanographic factors. Possible engineering solutions may exist in the field of ship construction and hull forms. Land-based, solid-wall, recirculation and reuse technologies known as Recirculating Aquaculture Systems (RAS) exist and are used for the culture of high-value fish species that can be reared in fresh, brackish and/or salt water. This technology also shows promise for the rearing of salmon in fresh or brackish water due to the great potential for reducing energy costs associated with the pumping of sea water. In addition, the greatly reduced water requirements with RAS may permit the added expense of disinfecting of influent and/or effluent water in order to reduce pathogen transmission. However, a critical evaluation of the potential for rearing Atlantic salmon in fresh/brackish water is required.
- A set of water quality parameters for the successful and healthy rearing of Atlantic salmon has been identified based on the available scientific literature. However, whether the available technologies can adequately meet these standards in salt water with fish 5 kg or greater still needs to be evaluated. The standards themselves need to be validated in practice.
- There needs to be further work to assess the animal welfare aspects of rearing salmon at densities higher than currently practiced.
- Changes to the husbandry environment involving closed-containment technologies, including increases in fish densities and hydraulic retention times, could increase the risk of pathogen exposure and horizontal transmission, relative to current systems. Disease risk assessments and quantitative monitoring of pathogen movement into, within and released from closed systems are required in order to identify critical control points. This information would then be used to more accurately deploy additional procedures and technologies aimed at reducing pathogen movements and disease risk.
- The environmental impacts associated with net pen aquaculture and closed-containment alternatives must be fully assessed to provide a framework for evaluating the environmental performance of the various systems in order to provide advice to governments regarding their support for potential technology development and research.
- A collegial group of interested parties with a wide range in expertise and opinions has been established during the CSAS process. This group should be utilized and consulted on future considerations related to the complex question of closed-containment technologies for aquaculture.
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