HIGH RESOLUTION MEASURES OF CURRENT FLOWS AROUND SALMON CAGES TO GUIDE THE PLACEMENT OF EXTRACTIVE SPECIES FOR INTEGRATED MULTI-TROPHIC AQUACULTURE  

In the Bay of Fundy, Canada, Integrated Multi-Trophic Aquaculture (IMTA) is currently operating at a small number of commercial Atlantic salmon farms. IMTA practices aim to culture species from various trophic levels, for partial recapture of different nutrient waste streams, to augment nutritional inputs for co-cultured extractive species (non-fed). Considerable research has investigated candidate species for IMTA, some of which include blue mussels, kelps and green sea urchins. Where IMTA is practiced at commercial salmon farms, cage configurations are typically reflective of the initial salmon cage layout. Consequently, placement of extractive species may be a function of space availability and not necessarily located to optimize nutrient capture. The objective of this study is to determine if near-field flows can be used to guide the placement of extractive species on IMTA farms.

Near-field current flows around Atlantic salmon cages were measured by a towed Acoustic Doppler Current Profiler (ADCP, River Ray). Farms were surveyed during ebb and flood tide, with data binned in 1 m depths. Contour plots were created at multiple depths to visualize flow within a farm lease area. Results to date suggest that near the surface, finfish cages can dampen flow speeds under certain configurations and environmental conditions. However, as depth increased, apparent effects from cages were diminished and flow typically became more uniform. Overall, flows within and between farms are highly variable, suggesting flow-fields are predominantly a function of local topography, tidal influences, environmental conditions and number and arrangement of cages. We explore how these results may influence delivery potential and effective IMTA design.