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The presence of in-feed anti-sea lice drugs and their relationship with organic enrichment is poorly understood in sediment surrounding salmon farms. Using data from an aquaculture monitoring program (2018–2020), we describe this relationship at ten sites in four Canadian provinces. Three anti-sea lice pesticides (lufenuron, teflubenzuron, emamectin benzoate and metabolite desmethyl emamectin benzoate), and one antibiotic (oxytetracycline) were detected. Concentrations were often below limits of quantification. Values are also lower than those reported in other aquaculture salmon-producing countries. Highest concentrations, along with organic enrichment, were observed ~200 m of cages with lower concentrations detected up to 1.5 km away. Most samples had at least two drugs present: 75.2 % (British Columbia), 91.4 % (Newfoundland), and 54.8 % (New Brunswick/Nova Scotia) highlighting the potential for cumulative effects. Emamectin benzoate and oxytetracycline were detected four and three years respectively after last known treatments, demonstrating the need for research on overall persistence of compounds. [Display omitted] • Sediment data collected through an aquaculture monitoring program were used. • Three anti-sea lice drugs and one antibiotic were detected at ten salmon sites. • The highest concentrations and organic enrichment were observed within 200 m of cages. • Most sediment samples had at least two drugs present. • There is a significant patchiness in drug presence and organic matter enrichment. [ABSTRACT FROM AUTHOR]

Abstract: Aquaculture structures may function in a manner analogous to artificial reefs, in that they provide a complex three-dimensional habitat for marine organisms and/or modify the surrounding environment. Further, aquaculture structures may increase the productivity of fish and macroinvertebrates similarly to natural complex habitats, such as seagrass beds. This research tested the general hypothesis that suspended bivalve culture increases the abundance and productivity of fish and macroinvertebrates. The study was done at two mussel farms in the Magdalen Islands, eastern Canada. Fish and macroinvertebrates were sampled in different areas within farms sites and in adjacent natural vegetated and unvegetated habitats. The instantaneous growth rates of winter flounder (Pseudopleuronectes americanus), sand shrimp (Crangon septemspinosa) and the rock crab (Cancer irroratus) were estimated using physiological indicators (RNA/DNA ratios). The results demonstrated that mussel sites are not equivalent to natural structurally complex seagrass beds with respect to fish and macroinvertebrate assemblages. Several species were abundant in mussel farms, including winter flounder and rock crab. This work, however, provided little evidence to suggest that there was greater productivity of these fish and macroinvertebrates at mussel farms, as growth rates were usually equivalent in different habitats. This study, to our knowledge, is the first attempt to determine changes in productivity brought about by aquaculture. As future development of mussel aquaculture increases in many regions around the world, the methods presented here will provide baseline information on the abundance and productivity of fish and macroinvertebrates associated with aquaculture sites. [Copyright &y& Elsevier]

Several trace-elements have been identified as indicators of finfish aquaculture organic enrichment. In this study, sediment sampling at finfish farms was completed as part of an Aquaculture Monitoring Program in three distinct Canadian regions. Despite diverse datasets, multivariate analyses show a consistent clustering of known direct (Cu and Zn) and indirect (Cd, Mo and U) tracers of aquaculture activities with sediment organic matter (OM) and/or total dissolved sulfides concentrations. OM content was also a predictor of Cu, Zn, Mo and U concentrations according to decision tree analyses. Distance from cages did not emerge as a strong driver of differences among sampling points; however, a tendency towards negative associations is clear especially for Zn. Enriched stations as determined after geochemical normalization were mostly localized within 150 m of net-pens. Selected trace-elements (in particular Zn) can be useful indicators of aquaculture organic enrichment in different ecosystems and valuable tools for monitoring programs. • Sediment sampling at finfish farms was completed in three distinct Canadian regions. • Multivariate analyses show a clustering of Cu, Zn, Cd, Mo and U with sediment organic matter and/or total dissolved sulfides. • Organic matter content is a predictor of Cu, Zn, Mo and U concentrations as per decision tree analyses. • Enriched stations in selected trace-metals were localized within 150 m of net-pens. • Selected trace-elements (in particular Zn) are useful indicators of aquaculture organic enrichment. [ABSTRACT FROM AUTHOR]