Predicted Nutrient Enrichment by Salmon Aquaculture and Potential for Effects in Cobscook Bay, Maine

Abstract

Salmon aquaculture has been a prominent feature of Cobscook Bay since the late 1980s, providing jobs in an economically depressed area of the State of Maine. Rearing finfish in moored floating pens is not without environmental consequences, however, with waste feed, feces, and dissolved nutrients discharged directly to surrounding waters. Near-field benthic effects have been well studied in Cobscook Bay, but far-field effects of nutrient enrichment from salmon aquaculture have not. Via two independent indirect methods, this paper estimates the amount of nitrogen and phosphorus discharged by salmon farms in Cobscook Bay. Results suggest that between 1995 and 1996, during the Cobscook Bay research program, salmon aquaculture contributed an annual load of about 360 metric tons of nitrogen and 85 metric tons phosphorus to Cobscook Bay. Compared to the already high nutrient flux from sources outside Cobscook Bay, we conclude it is unlikely the incremental contribution from aquaculture is measurably enhancing planktonic primary production. However, we acknowledge the need for further study on benthic macroalgae.