Catching characteristics of four fish-trap types on the North West Shelf of Australia

Commercial catch rates for the North West Shelf trap fishery, at up to 10 kg trap-' h-', are considerably greater than those reported for similar trap fisheries elsewhere. Two fish-trapping experiments were conducted off Lowendal Island (north-western Australia) to study the catch rates of four trap types (0-, S- and Z-shaped and rotational) and two bait types (pilchard, Sardinops neopilchardus, and emperor, Lethrznus choerorynchus) over various soak times (ranging from 1 to 24 h). Total catches varied significantly with soak time. Catches increased rapidly for the first 3 h, levelled off, and then decreased steadily to 16 h; there was a slight increase at 24 h. The species composition of the catch did not vary significantly with soak time. There was no significant difference in catch rates between trap types. The traps did not appear to cause fish to die by being confined in the traps for extended periods. A fairly large amount of suitable bait (about 4 kg) was necessary for effective trapping of fish. The catch rates of the pilchard bait were significantly higher than those of the emperor bait. Over extended soak times (more than 3 h), pilchard bait was lost at a rate of about 6% h-'. >.:hereas there was no detectable loss of emperor bait.