Field demonstration of a novel towed, area bubble-plume zooplankton (Calanus sp.) harvester

This paper presents the field testing of a new technology to harvest marine copepods (Calanus sp.) by bubble-induced upwelling. Two large-scale bubble rafts, a 21m2 and a flexible 75m2 bubble raft with tow-parallel and tow-perpendicular sparger elements, respectively, were tested in the sea with high Calanus densities in the upper 25 m. Bubble-driven upwelling velocities (Vup) measured with different air flows (Q) and source depths (z0), gave Vup ∼Q0.27 with stratified water, and were in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column: up to 1416%, with the best results for the transverse sparger raft, which also was tested with weak stratification. Bubble trawl performance also was affected by the stratification, with the highest enhancement for the lowest stratification. Catch species analysis showed reduced bycatch. Thus, this new harvesting technology showed a potential to develop an economically robust, environmentally benign, and sustainable fishery on a renewable resource at lower trophic levels in the food web, within the context of ecosystem-based management.