Exploitation of nutrients from Salmon aquaculture, EXPLOIT

To increase our knowledge about the potential for IMTA in Norway the main objectives of EXPLOIT were to: (I) Quantify spatial and temporal dynamics of the supply and availability of dissolved inorganic and particulate organic nutrient released from salmon farms in open coastal and sheltered fjord environments, (II) Characterise net accumulation of farm-derived dissolved nutrients and investigate the potential of seaweed growth in IMTA under Norwegian coastal conditions, (III) Quantify the assimilation capacity of farm-derived organic waste particulates by mussels and scallops in IMTA under Norwegian coastal conditions, (IV) Use mathematical modelling to estimate the potential for IMTA under Norwegian coastal conditions, and (V) Improve stakeholder perception of cage aquaculture. The project was led by SINTEF Fisheries and Aquaculture with Institute of Marine Research, NTNU Department of Biology and Department of Sociology and Political Science, Bedford Institute of Oceanography, Yellow Sea Fisheries Research Institute and Bellona as partners. Three field campaigns were conducted during the course of one production cycle at an open coastal farming location (Flåtegrunnen, Florø) in a coastal area in Western Norway. The spatial magnitude of fish effluent dispersion was limited; enhanced ammonia concentrations were only detected up to 100m down-current of the fish cages, and enhancement of fine particulate wastes were absent. Short-term temporal variability in ammonia concentrations was significant: the estimated level of impact varied up to 2 times from day to day (daily), and concentration besides cages were 3.5 times higher in the evening compared to the morning (diurnal). Finally, it was confirmed that large waste particles settle quickly to the seafloor (vertical transport), and dispersion of large particles is therefore limited to a few hundred meters from the farm: organic benthic deposition was more than 7 times higher at 100m from the last fish cage, at 200m sedimentation was double and at 400m similar to the references. An IMTA experiment was conducted at Flåtegrunnen in Western Norway from February to September 2013. Seaweeds, blue mussels and scallops were kept at 100 and 200 m distance and at two reference stations 1000 m away from the salmon farm (3000 ton standing stock in September)Tracer fatty acids in the digestive gland of blue mussels and scallops indicated that the supply of farm-derived wastes was limited to a distance of up to 100m down-current of the fish cages. Although the intensive salmon farming in Norway take place within low seston (oligotrophic) environments, the presence of a consistent and significantly elevated supply of waste particles to help enhance bivalve co-culture was not supported by the results. The majority of large particulates settle within a few hundred meters of the farm. Despite that fatty acid results demonstrates fish waste uptake in direct proximity of the farm, absence of enhanced supply of fine waste particles and waste capture efficiency estimates argue against a strong biomitigation potential of bivalves in IMTA. Although EXPLOIT did not investigate the biomitigation potential of deposit feeders, this seems to have potential for farm scale IMTA. Seaweeds grew significantly faster at 100m than at 200m and 1000m away from the fish cages. The model simulations indicated that for a salmon farm producing 5000 t a year, the kelp DIN extraction capacity was about 0.5 % of the effluent per hectare of kelp culture area. However mass balance approaches at regional scale seems promising for seaweed-fish IMTA interactions. Further simulation results indicated that while, generally, the largest effluent rates from fish farms come in late summer/early autumn, the greatest uptake capacity by kelps happens in spring. Thus there is a seasonal mismatch between effluent and extraction rates, partly determined by physiological processes in kelp. From a regional perspective the mass balance perspective and kelp biomass production potential is great. Thus for inorganic extractive species (kelps) in a farm scale IMTA system the bioremediation potential is relatively low, but the biomass production potential is high. Salmon farms in Norway contribute to good economy, but also introduce political, social and environmental challenges for the coastal communities where they are located. To improve coastal zone management, local governments frequently include stakeholders in the decision making process. IMTA as a production strategy creates new challenges for government (aquaculture policy), society (use of natural resources), and business (unproven economic benefits). However, there are opportunities for society if IMTA brings new sources of seafood and improved environmental status, and business opportunities through improved public perception.

The production of salmon and trout in Norway was 1,016,586 tonnes in 2009, with a use of 1,172,584 tonnes of fish feed (FHL, 2010). A considerable amount of the feed used is released to the surrounding waters, as respiratory products, faeces and uneaten f eed. There is an increasing concern regarding negative environmental impacts associated with this nutrient load, and one of the major challenges for the sustainable development of salmonid mariculture is therefore to minimize waste discharges that potenti ally lead to degradation of the marine environment. Integrated Multi-Trophic Aquaculture (IMTA) aims at reducing environmental effects and at the same time increasing the value of the produce. This can be done by cultivating extractive and filter feeding species at lower trophic levels in close vicinity to the fish farms. By combining field and laboratory studies with model development and socio-economic considerations SINTEF, NTNU and IMR intend to make a broad approach to investigate the potential for IMTA in Norway. In the project, critical hydrodynamic, chemical and biological variables will be monitored. Cultivation experiments in the trophic chain of salmon aquaculture, seaweeds and blue mussel will be performed at exposed (ACE, Bjugn) and sheltere d locations. 3D hydrodynamic and biological models will be used to tie together the gathered data and to evaluate the full scale potential of IMTA at ACE. The project will contribute siginificantly to improving the sustainability of the intensive fish fa rming industry. The project will provide new insights into the dynamics of IMTA, suggest practices for IMTA in Norway, and also suggest how ITMA may contribute to improve the public perception of cage aquaculture.