Finfish aquaculture results in the production of particulate waste products that include uneaten feed and faeces. The impact of these wastes on the suspended particle field at 4 open-water fish farms in Canada was studied using high-resolution in situ particle sensors. Within-pen sampling at a sablefish Anoplopoma fimbria farm in British Columbia provided some evidence of the release of low levels (mean effect < 0.2 mg l −1 ) of waste feed near the surface (1−3 m depth), but no waste signal was detectable in surface waters outside this farm. Enhancement of the particle field was also not apparent in surface waters (0.5−2 m depth) within the boundaries of an Atlantic salmon Salmo salar farm in the Bay of Fundy. However, data collected outside 2 adjacent farms indicated periodic, low-level particle enhancement (significant mean effect of <1.0 mg l −1 ; p < 0.001) near the surface immediately down-current from the net-pens. Despite the large sample numbers obtained, consistent detection of waste particle enhancement was confounded by the apparently small effect size and natural seston patchiness. These results suggest that any farm-induced effect on the surrounding particle field at the study sites would be highly localized and episodic. Consequently, the potential for enhanced production by co-cultured bivalve filter-feeders at these integrated multi-trophic aquaculture farms is limited by available space close to net-pens and the periodic availability of low levels of suspended particulate fish wastes.

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The organic enrichment of surficial sediments has a known effect on benthic faunal communities due largely to oxygen depletion and sulfide toxicity. Total dissolved sulfide (free S=HS+HS+S) concentrations in sediments are widely measured as a practical indicator of community effects. However, the standard ion selective electrode (ISE) method for free S analysis can provide biased results owing to the inclusion of non-toxic mineral sulfides and the oxidation and volatilization of free S. A rapid field protocol was developed that alleviates these problems while also providing data on dissolved oxygen concentrations. Sediments collected near salmon aquaculture pens over cohesive and permeable substrates were analysed using the standard and new protocols. The results confirm previous conclusions of artifacts with the standard ISE method, while the dual indicator approach more accurately describes the stages, spatial extent and magnitude of sediment geochemical alterations affecting benthic communities.