Abstract
While environmental performance of cage-based aquaculture is most often monitored through benthic conditions, there may also be requirements that necessitate discrete, pelagic sampling. In the pelagic realm, adequately capturing the spatial and temporal dynamics of interest and attributing causality to aquaculture processes can be extremely challenging. Conditions are seldom ideal, and data adequacy concerns of discrete samples collected at open-water aquaculture sites are not uncommon. Further exploration of these challenges is needed. Herein, we aim to explore considerations for study design, analysis, and data interpretation of discrete pelagic sampling. As examples, we present 2 case studies where limited sampling occurred under conditions of complex pelagic dynamics. A Norwegian case study quantified particle abundance around salmon farms, and aimed to highlight the effects of spatial−temporal variation on sampling design, the need for inclusion of companion parameters, and the benefits of a priori and a posteriori data interpretation strategies. A Canadian case study collected discrete samples to measure ammonium concentrations with continuous current measurements at an Integrated Multi-Trophic Aquaculture (IMTA) farm, to explore issues of complex hydrodynamics, reference site suitability, sampling resolution, data pooling, and post hoc power tests. We further discuss lessons learned and the implications of study design, ambient conditions, physical processes, farm management, statistical analysis, companion parameters, and the potential for confounding effects. Pragmatic consideration of these aspects will ultimately serve to better frame the costs and benefits of discrete pelagic sampling at open-water aquaculture sites.
Highlights
Increased environmental concerns about the release of effluents from open-water finfish culture have prompted monitoring and modelling to assess the potential negative impacts (Holmer et al 2008) and approaches to utilize waste nutrients, such as Integrated Multi-Trophic Aquaculture (IMTA; Chopin et al 2012)
Results of this case study demonstrated that detection of enhanced particle abundance around fish cages may not be solely a function of salmon farm waste, but potentially of local influences and sampling effects
With the current sampling design we were not able to differentiate between farm- and non-farm-related factors, but a priori and a posteriori data interpretation strategies helped to place the right level of confidence in the obtained results
Summary
Increased environmental concerns about the release of effluents from open-water finfish culture have prompted monitoring and modelling to assess the potential negative impacts (Holmer et al 2008) and approaches to utilize waste nutrients, such as Integrated Multi-Trophic Aquaculture (IMTA; Chopin et al 2012). At Site I, vertical profiles of companion parameters, such as temperature and salinity, showed similarity between the farming and reference stations (Fig. 3B,C) This suggests that the water body close to the farm was representative of the surrounding environment, and differences in particle abundance can be attributed to waste release from the farms. The vertical distribution of fish biomass at the time of sampling was unknown, but 15 m could possibly be the depth of maximum biomass according to the farm manager Were this the case, cooler, less saline, particle-rich surface water might be drawn down through the cage, exiting at lower depths. Results among the 3 spatially separated reference stations were consistent for both sites, indicating a homogeneous water mass in the study area This suggests that the observed differences are a result of spatial/temporal hydrodynamic effects rather than induced by geographical variances between reference and farming stations
Published Version
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