| Summary: | Farm based monitoring has shown copper concentrations in sediments under salmon farms in the Huonand DEntrecasteaux Channel are elevated relative to background conditions as a result of long-term useof copper-based antifoulants. This study was undertaken as a collaboration between researchers at theInstitute for Marine and Antarctic Studies (University of Tasmania) and CSIRO, and with the cooperationof the Tasmanian Salmon farming industry to determine whether these copper concentrations have anymajor or long-term impacts on the local ecology or sediment function and to identify the remediationpotential of these sediments and what, if any, management strategies could be used to enhance recovery.Noting that in this instance recovery was assessed as either i) a marked decline in copper over time(recovery in progress) or ii) return to background/ baseline copper concentrations (total recovery).Conditions were assessed over the short-term (12 months, this study) at sites selected for high copperloads, as well as over the longer-term (> 5 years, incorporating the results of previous farm-basedassessments) at sites where the copper concentration history was well-known. Changes in backgroundconcentrations were assessed by reviewing copper data from both the farm assessments and a range ofprevious studies in the region, and integrating broader environmental data on prevailing conditions andexposure. Finally, targeted sedimentation studies provided data on deposition and accumulation rates thatcould be used to provide longer-term projections for recovery.A specific concern at the start of this study was that ongoing farming, even without the use of antifoulantnets, could increase the risk of toxicity in sediments where copper concentrations were elevated; theresults of this study clearly identify that this is not the case. The results indicate that the risk of seriousadverse impacts on sediment processes from current copper contamination levels is relatively low; largelybecause most of the copper occurs as paint flakes and cant be easily taken up by benthic organisms.Copper can exist in a variety of forms in the sediments, with some being more toxic than others. Theconcentrations of relevant forms of copper were assessed, and the associated sediment conditionsdetermined. Whilst antifoulant usage was shown to be the primary source of elevated copperconcentrations within farms, local environmental conditions and certain farming practices can have asignificant influence on copper accumulation and impact levels throughout the system. Consequently, itwas possible to make operational management recommendations that will reduce the potential for impactsinto the future. The study also recommends refined regulatory guidelines that should provide betterprotection with respect to chronic ecotoxicological impacts.
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