Technical and economical feasibility of integrated salmon and kelp production system

The purpose of this study was to evaluate the technical and economical feasibility of Laminaria saccharina culture near asalmon netpen farm. A computer model was developed to make this assessment. The availability of ammonia nitrogen from the netpens and its diffusion into the kelp were included in the model. Laminaria production is based on nitrogen availability, light and water temperature. Light intensity, including its availability and attenuation, was incorporated into a submodel. This submodel could be used to manage the light intensity on a kelp farm (i.e. by changing the depth of kelp ropes). Based on model predictions, a Laminaria farm containing 10 60m ropes on each end of a salmon netpen farm is technically feasible and is fertilized by the salmon farm. A yearly production of 1600kg of kelp (dry basis) and a net profit of $20,000 are expected by this size of farm (selling price = $35 per kg dry mass). Kelp production on multiple salmon farms or with more kelp ropes could increase the overall net revenue of the owner. Larger-sized kelp farms may, however, need artificial fertilizer. The average rate of light radiation for good kelp growth should not exceed 100 µE m⁻² s⁻¹ and should not be less than 30 µE m⁻² s⁻¹. Light intensity for different depths and attenuation coefficients can be predicted by the light submodel, and thisinformation can be used as a kelp farm management tool. Light availability depends on the season of the year and water condition. By using this submodel, the optimum depth of a kelp raft for growth can be determined. A 47% reduction in light intensity is observed when light travels from a depth of 2 to 7 m (attenuation coefficient = 0.1 m⁻¹). A set of experiments was conducted at the Department of Fisheries and Oceans facilities (July-August 1991) to examine Laminaria growth at different salmon-effluent nitrogen concentrations and to validate the Laminaria growth model. The experiment was a model of an actual kelp farm near a netpen (i.e.similar water velocity and tidal effects). The model was validated for ammonia nitrogen concentrations of less than 5 AM. A direct relationship between growth rate, and ammonia nitrogen and nitrate availability was found. For a combined nitrogen concentration of ammonia nitrogen and nitrate of 9.7 µM, a specific growth rate of 9% d⁻¹ was obtained. A second set of experiments was conducted to measure the oxygen consumption rate of the kelp. The results were used in the computer model to determine if kelp farms would cause an oxygen deficit for fish in the netpens at night. The consumption rate was found to be 0.024 mg 0₂ g kelp⁻¹ h⁻¹. This result was used in the model to compare oxygen availability versus oxygen consumption rate. The results from the model were used to show that for a 10x 60 m rope kelp farm, oxygen consumption at night was less than 1%of the oxygen available to the fish in the netpens. Therefore, oxygen consumption at night by a 10 x 60 m rope farm would not cause significant oxygen depletion for fish.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat