Department of Marine Science and Technology, Tokyo University of Fisheries, Tokyo 108-8477, Japan
The SURF-BRD is comprised of two panels (front panel with large mesh and rear panel with small mesh) and two side escape-vents for fish escapement. Only fish that pass through the front panel can escape from the side escape-vent and hence the BRD has size selectivity of the front-panel mesh size for fish encountering it. To ensure size selectivity in the improved BRD trawl, the selvedge ropes to which the ends of the front-panel headline were attached was installed at the center of the belly, which is 1.5 times higher than the prototype BRD trawl. This study examined four factors (buoyancy of floats on the BRD headline, the angle of rear panel, the volume of catch, and towing speed) affecting the height of the BRD and the trawl using a 1/10-scale model in a circulating water tank. The BRD height was strongly affected by the towing speed and the buoyancy of the floats with its relationship to the configuration of the whole trawl net. At the towing speed of two knots with catch in the cod-end up to 40kgw, the BRD trawl with the BRD headline floats of 6.5kgw buoyancy and the rear panel installed at the angle of 45 degrees can keep the BRD height about 1.0 meter.