| Summary: | Salmon aquaculture is a controversial industry in British Columbia (BC). First Nations in BC have expressed concerns about possible contamination of traditionally harvested foods by waste from salmon farms. Trace elements are released from farms via waste feed and feces, as well as leaching from netpens and antifouling paints. In addition to elemental analysis, farm waste can also be traced using stable isotopes of nitrogen and carbon. Due to the use in salmon feed of protein and oil derived from pelagic marine fish, farm waste is typically enriched in heavier isotopes of nitrogen and carbon when compared to marine particulate organic matter. in partnership with First Nations from Ahousaht, BC, I investigated these effects by determining the concentrations of three metals and one metalloid in salmon feed, sediment and Manila clams Venerupis philippinarum from six sites in Clayoquot Sound, on the west coast of Vancouver Island, BC. Samples were collected from three sites near salmon farms and three reference sites in four different months spanning the traditional clam harvesting season. The results suggested that salmon feed continues to be a source of trace elements in the marine environment; however, salmon farms did not appear to be elevating concentrations in nearby clam tissue and sediment. Different environmental conditions between sites may have exerted a greater influence on elemental concentrations than farm-derived elements. Contrary to findings in earlier studies, the nitrogen signature of salmon feed was not enriched relative to marine particulate organic matter and was not a useful tracer of farm waste. This may have resulted from the reformulation of salmon feed to include greater quantities of protein and oil from terrestrial rather than marine sources. Due to the importance of Manila clams in First Nations' diets, the high density of salmon farms in the study area, the likelihood of ongoing feed reformulation, and the propensity for contaminants to accumulate over time, ongoing monitoring of ...
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