No effects of ground-gear diameter on the performance of a south-eastern Australian fish trawl

As part of attempts at improving the selectivity of south-eastern Australian fish trawls, the effects of ground-gear disc diameter on trawl engineering and catching performances were investigated. Three conventional disc di-ameters (100 mm or 4 in., 178 mm or 7 in. and 254 mm or 10 in.) at the centre third of the ground gear were alternated during 12 days of conventional fishing. There were no significant effects of ground-gear configuration on otter-board spread or the headline height of the trawl. Rather, significant influences were limited to depth affecting positive and negative relationships with otter-board spread and headline height, and speed over the ground evoking a positive effect on otter-board spread. Catches of four retained species (bigeye ocean perch, Helicolenus barathri, pink ling, Genypterus blacodes, ocean leather jacket, Nelusetta ayraud, and tiger flathead, Platycephalus richardsoni) and two discards (smooth whiptail, Malacocephalus laevis and falseband whiptail, Coelorinchus maurofasciatus) and the sizes of three of these species, were not significantly different among ground gears. The results imply minimal benefit in varying conventional ground-gear configurations for reducing un-wanted catches.