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

Abstract

This paper presents field experiment results of using a new technology to harvest copepods (Calanus sp.) in the ocean by bubble upwelling. Two largo-scale bubble rafts, a 21 m2 and a flexible 75 m2 bubble raft with tow parallel and perpendicular sparger elements, respectively, were field tested in areas with high, upper 25-m water column Calanus densities. Measured bubble-driven upwelling velocities (Vup) at different air flows (Q) and depths (z0), found Vup-(f21 under stratified marine conditions, in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column, as much as 1416% integrated over the upper 2·m, with the best results for the tow-transverse raft, which also was tested under unstratified seas. Bubble trawl perfonnance aJso was related to 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