Environmental impacts of salmon cage aquaculture resulting from deposition of organic-richparticulate matter to the sea bottom have been thought to be a function of the local environmentalconditions and management practices. However, testing of these suppositions have been limited by(1) widely varying monitoring methods employed, and (2) lack of data comparability resulting fromthe absence of standardized national monitoring schemes.In order to determine the sensitivity of different monitoring methods in detecting benthicenvironmental effects, a comparative analysis was undertaken of four methods commonly employedin Norway that vary in cost and expertise required: (1) visual diver surveys, (2) faunal analysis, (3)sediment chemistry, and (4) Sediment Profile Imagery (SPI). Results indicate that all methods agreedin the common ‘‘impact zone’’ under and immediately next to the cages. However, each of themethods differed in their sensitivity in detecting more subtle effects at greater distances from thecages.Data from 168 environmental survey samples located at various distances from workingNorwegian salmon cage farms collected using similar methodology between 1996 and 1998 wereanalyzed to determine the relationship between environmental variables, management regimes, andlevels of environmental impact. Total organic carbon (TOC) levels in sediments were significantlyhigher immediately adjacent to cages compared to reference sites, and approximately 32% of thesamples under the cages showed significant degradation. At intermediate distances (50-100 m),influences from fish farming are not clearly detected by TOC analysis. Further, while neither depthnor current speed alone are good predictors for environmental management, the results suggest recovery of sites by periodic abandonment (or fallowing) is one of the best management tools forsustainable salmon farming in cold-water environments.
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