On the modeling of waste deposition around deep aquaculture sites in Newfoundland / by Andry W. Ratsimandresy, Dounia Hamoutene, Brent Law, Vanessa Oldford, Flora Salvo, Aaron Bennett.: Fs97-6/3745E-PDF

"Finfish aquaculture in Newfoundland includes a grow out phase in open-net cages often set up in deep fjord-like sites. With the expansion of the industry and the concern for environmental impact, two coastal steep and deep sites located in the same bay were studied in order to analyze the deposition associated with the farming activity. Ocean currents at various depths were measured for seven months at one location close to each farming site. These currents together with weekly feeding data were used to force the deposition model DEPOMOD which computed the dispersion and deposition of waste from the farms. The modeled performance was assessed by comparing computed waste deposition to direct deposition measurement obtained from programmable sediment traps and to seafloor video observations. Our analysis of the model output shows that deposition can take place at a distance greater than 500 m away from the cage array; however, the location of the deposition would vary depending on the vertical resolution of the ocean current data used to force the model, thus leading to a variation in the site footprint. Our findings show that DEPOMOD has important limitations in reproducing the observed waste deposition at the coastal deep environment where finfish farms are located in Newfoundland and in explaining the benthic survey observations. Consideration of resuspension in the model run can also generate larger footprints. For instance, in the present study, less than 2 % of the recorded current speeds were over the resuspension threshold; however, the amount of deposition happening outside of a 1000 x 1000 m² domain changed from 6 % to 60 % of the total expected deposition between the DEPOMOD run without resuspension and that with resuspension, neither of the case runs explained the observed deposition"--Abstract, page vii.

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