Near-Field Depositional Model for Salmon Aquaculture Waste

Abstract

An analytical near-field depositional model for solids wastes (organic matter from waste feed and faeces) from open net pen culture of finfish is presented. The model is based on the premise that the statistics of the depth-averaged currents, which are assumed to be normally distributed, determine the distribution of wastes on the ocean bottom. Using a farm configuration consisting of a single net pen, the model is used in a diagnostic mode to quantitatively examine the effects on the waste depositional field or footprint of the farm that result from changing the depth under the net pens and changing the statistics (standard deviations) of the depth-averaged velocity. The model is also used to examine the changes to the farm footprint that result from orientating a two by four linear grouping of net pens perpendicular to and parallel to the principle current direction. The model was tested on an operating Atlantic salmon farm by comparing the predicted organic matter fluxes from the farm with the vertical fluxes of organic matter measured by sediment traps. Based on a rather limited data set, predicted organic matter fluxes were found to be about four to five times higher than observed sedimentation rates. Further, the model predictions were sensitive to the value used for feed waste. The limitations and uncertainties in the model assumptions, parameterizations and in the methodologies used to validate the model are discussed and recommendations for future research are provided.