Selectivity for barramundi (Lates calcarifer) in the Fly River, Papua New Guinea: Implications for managing gill-net fisheries on protandrous fishes

Fishery-independent catch data from monofilament gill-nets (3.8-15.2 cm stretched mesh) were used to estimate the selectivity of each mesh size for the protandrous species barramundi, Lates calcarifer, in the Fly River region of Western Province, Papua New Guinea. These results were used with a range of life-history parameters to simulate the effects of fishing with meshes of three sizes common to the local fisheries (8.9, 10.2 and 15.2 cm) on (1) number of sexually mature females surviving to maximum age, (2) their total egg production and (3) number of mature males surviving to fertilize these eggs. Catches in most mesh sizes approximated a normal selection curve, and the mean and standard deviation of each curve were linearly related to mesh size. Juvenile and immature barramundi (<38 cm total length) were fully selected by the common mesh sizes used in the coastal subsistence and artisanal fisheries (7.6-10.2 cm) but these mesh sizes caught few sexually mature females. Population simulations showed that the number of females surviving to maximum age and their total egg production increased as mesh size was reduced. Reducing the mesh size to increase adult female escapement may be a better management strategy than increasing mesh sizes to improve recruitment.