Rigid and flexible separator panels in trawls that reduce the by-catch of small fish in the Clarence River prawn-trawl fishery, Australia

Two experiments were done in the Clarence River prawn-trawl fishery that compared catches and by-catches from conventional trawls with those from modified trawls containing rigid and flexible separator panels. The modifications included (1) a soft separator panel, the 'blubber-chute' (used commercially by fishers to exclude jellyfish), (2) the standard Nordmore grid, containing a guiding panel, and (3) a modified Nordmore grid that had no guiding panel but included a flexible cover of mesh lying semi-attached over the escape exit. In the first experiment, simultaneous paired comparisons among these designs and their controls showed that although all three modified trawls significantly reduced the by-catch of small fish by between 75% and 90%, the standard Nordmore grid was the only design that did not significantly reduce catches of prawns. In the second experiment, which compared this standard grid with the control during a period of flooding when the by-catch of non-target species was quite high, the standard grid significantly reduced the by-catch of juvenile bream (Acanthopagrus australis) (by 67%) with no significant reduction in catches of prawns. The potential for the Nordmore grid to alleviate deleterious effects of prawn trawling in estuaries is discussed