Effects of fish trap mesh size on species and size selectivity in the Australian North West Shelf trap fishery

Trap-introduced fishing mortality of juvenile fish was seen as a potential problem in the developing fish trap fishery on the Australian North West Shelf. Line fishermen are concerned that traps are unselective. Research to investigate the reality of the problem and to assess large-mesh traps as a solution found that: 1) Standard 5 x 5 cm mesh traps do catch many small fish; 2) 10 x 10 and 15 x 5 cm mesh traps catch few small fish; 3) Large-mesh traps are less efficient for big fish; 4) The small fish caught tend to be small-bodied species, not juveniles of more valuable large-bodied species; 5) Mesh size appears to have effects on trap efficiency independent of simple escapement through the mesh. Since juvenile mortality is not yet considered a problem, continued use of standard mesh traps is recommended. Future research aimed at identifying nursery areas for valuable species is suggested to enable protective area closures to be used by management.