Species- and size-selectivity of SURF-BRD trawl

This study describes species- and size-selectivity of SURF (System of Unwan ts Ramp-way Filter)-BRD, which was developed to avoid by-catch of juvenile fishes smaller than marketable size and small crabs of no-commercial value in a shrimp beam trawl. The SURF-BRD comprised of two square-mesh panels (F P, front panel and RP, rear one of 40 mm mesh bar) and two escape-vents, an d was installed on the bottom part of the net-mouth. Eleven tows with escap e-vent cover-nets for catching escapees from the vent were conducted under three panel conditions: 5 tows with the FP and RP; at 4 tows, rear cover (R C) of the same mesh size as the codend was attached over the RP to avoid an imals passing through the RP; 2 tows without the FP to examine the role of FP on selectivity of the device. The results of proportions caught in the c odend to the total by species and by animal size indicated three routes of the animals to the codend: 1) swimming above the BRD without encountering t he FP; 2) encountering the FP once and retained by it; and 3) passing throu gh the FP and also through the RP. The RP needs to have enough small mesh l ike the RC, to lead animals out of the net through the escape-vent after pa ssing through the FP. The SURF-BRD allowed some juvenile fishes and small c rabs to escape from the net, while catching small shrimp of the main target species at night.