Strategic development and research actions are needed to realize the Norwegian government’s long-term aim for a predictable and sustainable growth within the aquaculture industry1. Fish farming in Norway is dominated by sea cage farming of salmonid species (Atlantic salmon and rainbow trout). In recent years, the industry has experienced an augmentation in production volumes per farm while the number of farm locations has decreased2. This augmentation of production leads to increased feed use, and subsequently to augmented release of nutrients and organic particles released into the marine environment3,4. These nutrients and organic particles released from aquaculture represent a possible resource for new biomass cultures, but also a risk to the environment and sustainability of the fish production. Thus, improved resource and energy utilization must be investigated in order to transform the wastes into a resource for producing other organisms at other trophic levels with potential for creating high value products5. In Norway, IMTA systems could also be a way to increase seafood production in areas already occupied by/allocated for salmonid aquaculture.
MATERIALS AND METHODS
The data were collected through a desktop study of peer-reviewed and ‘grey’ literature to identify the reported IMTA research and industrial activities and investigate the incentives already in place to develop this technology in order to outline the upscaling potential of each technological approach in Norway.
Various research initiatives, both nationally and internationally, have been addressing IMTA related questions and are contributing to a gradual development of the sector, including the transition from research to commercial scale IMTA systems. In Norway, the IMTA research activities currently focus on increasing the knowledge about new potential aquaculture species and appropriate organism for co-culturing based on their trophic levels and complementary functions in the ecosystem, as well as their economic value or market potential. However, most studies on IMTA have so far been based on experimental designs with limited biomass of extractive species not yet allowing for thorough evaluations of biological and economical pros and cons of implementing salmon based IMTA as a production strategy.
There is still a reluctance to this concept of ecological engineering in Norway reflected by the lack of research on IMTA and development of new technologies for integration of species at lower trophic levels with today’s intensively fed monocultures of fish. At present there is uncertainty about the potential use of bivalves in IMTA, while macroalgae and deposit feeders seems more promising and are the scope for research environments and industry.
Seaweed has demonstrated having a high capacity for absorption and metabolism of inorganic nutrients excreted by fish aquaculture, integrating seaweed cultures in IMTA and seems promising for further upscaling of IMTA in Norway while producing valuable products of marine origin6. However, based on the current production technology, the seaweed value-chain will require extensive innovation and economies of scale to become energy competitive7,8 and to be competitive as a biomass source for the production of fish feed ingredients9. Further research should investigate the predictive environmental impacts of a fully developed seaweed value-chain and account for the emissions and multi-functionality of the system (e.g. lost biomass, impact on biodiversity, ecosystem services).
The particulate excess from salmon aquaculture can also be regarded as a food source for filter feeders in an IMTA system. Whereas feed waste constitutes only 3-5% of the feed distributed, most of the particles originate from feces production. Fish feces has a low nutritional value, but this food source still can support the growth of bivalves such as blue mussels in nutrient limited areas. Thus, to the best of our knowledge it has not been investigated whether running a whole cultivation cycle of mussels or scallops in IMTA with salmon in Norway yields higher bivalve biomass at harvest compared to monoculture production. Nevertheless, collected sludge from production of larger smolts in land-based systems before deployment at sea can be further fed as substrate and utilized by deposit feeders (e.g. polychaetes, sea cucumber) and currently presents one of the new opportunities for developing IMTA in Norway10.
Upscaling of pilot experiments with new sophisticated technological solutions and systems at industrial scale is a prerequisite for the quantification of the potential for bioremediation services and increased biomass production of the low-trophic species in IMTA in Norway. Although the aquaculture regulations are intended to secure a sustainable industry, they have not yet been fully adapted to suit the emerging integrated systems. Norwegian aquaculture activity is thoroughly regulated, and spatial issues related to minimum distance between aquaculture farms, co-location of species at different trophic levels, and zoning strategies has been used as main management tools to control disease transfer. Therefore, restrictions on co-location of multiple species on the same site and the limited environmental, economic and societal pressures and incentives from the industry and the public are important challenges to the develop commercial IMTA in Norway.