The use of separator panels and square mesh windows for by-catch reduction in the crustacean trawl fishery off the Algarve (South Portugal)

The utility of oblique separator panels combined with square mesh windows for reducing by-catch (mainly boarfish (Capros aper), blue whiting (Micromesistius poutassou) and horse mackerel (Trachurus trachurus)) was examined in the Algarve crustacean trawl fishery.\ud \ud Three different panel/window mesh size combinations and the window alone were tested. The results suggest that the amount of blue whiting excluded was independent of the use of the separator panel, as well as the mesh sizes of the panel and the square mesh window. Between 67 and 71% of the total catch of this species was excluded. The window mesh size however, significantly affected the escape of boarfish, with the average escape percentage released rising from 10 to 44% as the mesh size increased from 70 to 100 mm.\ud \ud The highest exclusion rates were obtained with the use of a 120 mm separator panel together with a 100 mm square mesh window. Under these conditions, the exclusion of by-catch was maximised while maintaining the catch for the target species(rose shrimp Parapenaeus longirostris, and Norway lobster, Nephrops norvegicus). In hauls where the square mesh window was used alone, only the escape rate of blue whiting was significant (67%), while boarfish escaped in much lower proportions and shrimp above the minimum landing size were lost. Despite the efficiency of these panels as by-catch excluders, their complex design is a major drawback to commercial adoption