Selectivity of penaeid trap nets used in south eastern Australia

Abstract

Two experiments were done to estimate the selectivity of commercial and modified trap-net configurations in New South Wales (NSW), southeastern Australia. In the first experiment, a commercial trap net made entirely from 25 mm mesh and designed for use in shallow water was alternatively fished with a fine-meshed (9.5 mm netting) trap net (used as a control). In the second experiment, two trap-net configurations designed for use in deeper water and comprising the same anterior section (made from 25 mm mesh), but with different bunts made from (i) the conventional 25 mm mesh and (ii) 31 mm mesh were alternately fished against the control. Both of the conventional trap nets (comprising 25 mm mesh throughout) had low amounts of bycatch and similarly selected eastern king Penaeus plebejus, greasyback Metapenaeus bennettae and school prawns Metapenaeus macleayi across narrow selection ranges (< 3.4 mm) and at 50% retention lengths (between 18.53 and 21.50 mm) that were larger than the average commercially-accepted sizes (15-17 mm CL). Analyses of the selectivities and relative efficiencies of the trap-net configurations comprising the 25 and 31 mm bunts showed no benefit, in terms of maintaining prawn catches and reducing unwanted bycatch, associated with increasing mesh size in these gears. The utility of trap nets for selectively harvesting penaeids is discussed. We conclude that this type of fishing gear appears to have few deleterious impacts.