Initial Tests of a Flexible Grate for Size Selection of Trawl Caught Fish

The fish size selection and handling features of a trawl-mounted flexible grate were tested. The grate was constructed of fiberglass rods and neoprene strips to be flexible enough to bend around a net reel, but rigid enough to maintain consistent, long, rectangular openings for fish size selection during trawling. A 244 cm × 140 cm grate, installed in the extension section of a bottom trawl, was tested for size selection of walleye pollock (Theragra chalcogramma) in the Bering Sea by means of a small mesh auxiliary net that collected escapees. A grate with 44 mm spacing had an L₅₀, the length at which 50% of the fish escaped, of 37 cm and a selection range estimated at 10 cm. Few fish longer than 44 cm escaped, corresponding to pollock with head widths equal to the 44 mm bar spacing. The grate was easily deployed and retrieved from a net reel, without any special gear handling procedures required. In-situ video observations using infrared illumination confirmed that the panel and collection net assumed their correct configurations and that escaping pollock passed easily through the grate.