Reconciling Coulter Counter and laser diffraction particle size analysis for aquaculture monitoring.

The disaggregated inorganic grain size (DIGS) of bottom sediment analyzed with a Coulter Counter (CC) has been used to show that the fraction of sediment deposited in flocs (floc fraction) increased in both the near and far field after the introduction of open cage salmon aquaculture, altering benthic habitat and species composition. As a result, DIGS was identified as a potential indicator of regional environmental changes due to aquaculture. Laser diffraction is an attractive alternative to the CC because of its greater efficiency and larger size range. To determine if a laser diffraction instrument, Beckman-Coulter LS 13 320 (LS), could replace the CC within a Canadian national aquaculture monitoring program, the DIGS of 581 samples from five different regions in eastern Canada were analyzed with an LS and a CC. Results show that the LS could not be used to calculate floc fraction. Instead, % sortable silt and the volume % of inorganic particles < 16 µm were evaluated as alternative proxies for fine sediment properties. LS and CC values for these parameters were correlated, but they were significantly different and the relationship between the instruments was dependent on the area sampled. The LS did not capture variations between areas seen in the CC DIGS data. Where the DIGS from the CC found no sorting in the finest size classes, all the LS samples had similar size distributions characterized by smooth modal peaks. The LS and CC both return values that can be used to monitor changes in the deposition of fine-grained sediment, but the LS cannot determine changes in floc deposition and caution is required if comparing different sedimentary environments.

Relationship between in feed drugs, antibiotics and organic enrichment in marine sediments at Canadian Atlantic salmon aquaculture sites.

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.

Assessing trace-elements as indicators of marine finfish aquaculture across three distinct Canadian coastal regions.

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.