Gillnet size selectivity of shark and ray species from Queensland, Australia

Gillnets are size-selective fishing gears commonly used by industrial and small-scale fishers, so understanding selectivity can aid fisheries management by identifying suitable mesh sizes to optimize catches of target species while reducing bycatch. Few size selectivity parameters have been estimated for sharks, with even fewer for rays. Size selection parameters were estimated for seven species of sharks and two species of rays from the Queensland East Coast Inshore Finfish Fishery (ECIFF). Size frequency data from a fishery observer program on ECIFF vessels was used to fit a standard size selection model. Mesh size independent parameters, theta(1) and theta(2), were estimated for each species to define selectivity curves for different mesh sizes for each species. Parameter values were compared with previous studies that used the same method. Estimates of theta(1) were similar among species within the same genus, such as Carcharhinus, Rhizoprionodon, and Sphyrna. Anoxypristis cuspidata had the largest theta(1) and theta(2) values, likely because of its toothed rostrum that affected catchability in gillnets. Our findings can be used for the ECIFF and other gillnet fisheries to aid in mesh size recommendations and risk mitigation.