Improving the performance of a generic fisheye as a secondary bycatch reduction device in a south-eastern Australian penaeid-trawl fishery

The utility of a generic device (termed a 'fisheye') and its simple modification for cumulatively reducing bycatch in penaeid trawls was assessed during two experiments in a south-eastern Australian fishery. In the first experiment, conventional trawls (with no fisheye) were compared to simultaneously towed, identical trawls installed with a typical fisheye (termed 'mesh fisheye') comprising an open triangular frame terminating in a semi-elliptical vertical opening (350 x 150 mm) in the top of the trawl extension at 1.1 m anterior to the codend drawstring. Trawls with the mesh fisheye maintained catches of penaeids (mostly school prawns, Metapenaeus macleayi) but retained significantly less total bycatch (by 39 %) and fewer unwanted southern herring, Her-klotsichthys castelnaui (by 60 %) and tailor, Pomatomus saltatrix (by 52 %). During the second experiment, trawls with the mesh fisheye were simultaneously compared to those with a modified design comprising a solid panel of aluminium in the lower half of the triangular frame (termed the 'solid fisheye'). The solid fisheye excluded significantly more bycatch (by 52 %) and small southern herring (by 47 %), and also the numbers of several other species, including mulloway (by 38-41 %) without affecting penaeid catches. The improved performance of the solid fisheye was attributed to its greater anterior displacement of water and posterior area of lower perceived flow for fish. The results and simplicity of the fisheye modification support not only its regional use, but also testing in other national and international fisheries.