The efficiency of sieve-panels for bycatch separation in Nephrops trawls

This study investigated the efficiency of a sieve-panel concept, intended to separate bycatch species from Nephrops (Norway lobster) in a trawl gear via mechanical and behavioural means. Four different designs of varying panel mesh size or inclination were tested in experimental fishing. For each design, the length-dependent sieving efficiency, defined as the fraction of Nephrops or fish passing through the panel to the lower codend, was estimated. The sieving efficiency for Nephrops increased from ~17% to ~71% as mesh size increased, and decreased with increasing carapace length, but did so less as panel inclination and mesh size increased. The sieving efficiency for roundfish was low, as intended, while the efficiency for flatfish decreased with fish size. Although results are promising, the sieving efficiency for the largest, most valuable Nephrops remained too low. Therefore, further improvements are necessary before the concept is acceptable to the commercial fishing fleet.