Trammel net and gill net selectivity for Lithognathus mormyrus (L., 1758), Diplodus annularis (L., 1758) and Mullus barbatus (L., 1758) in the Adriatic and Ligurian seas

Abstract

The selectivity of a traditional trammel net, a monofilament trammel net and a gill net for Lithognathus mormyrus (striped sea-bream), Diplodus annularis (annular sea-bream) and Mullus barbatus (red mullet) was investigated in two coastal areas (central Adriatic sea and southern Ligurian sea). Three mesh sizes were tested for each set net: 45, 70 and 90 mm (stretched-mesh size). Selectivity was assessed by the indirect Sechin model based on the measurement of maximum body girth and head girth. The 45-mm mesh size was the most efficient for all the target species irrespective of net type. The catches obtained with the 90-mm meshes were always very low as were the catches of D. annularis and M. barbatus with the 70-mm mesh. Although most fishes of the three target species were caught by gilling and/or wedging, with all gears a number of individuals were also caught by virtue of the tangled and/or pocket effects. Their proportion, lowest and generally negligible in the gill net, higher in the monofilament and highest in the standard trammel net, caused a progressive widening of size-catch ranges, confirming the low selectivity of trammel nets. The 45-mm mesh appears to be the most suitable for the exploitation of the target species because it caught the highest number of specimens while it largely spared the juveniles.