Net selectivity for Barramundi (Lates calcarifer)

Abstract

Log-linear modelling of two fisheries-independent barramundi catch and effort datasets (2000-2006 research survey data and 1981-1984 research survey data) from the east coast of Queensland provided estimates of selectivity of barramundi for seven mesh sizes from 101.6 mm to 203.2 mm. These estimates provide a basis for assessing the sensitivity of barramundi production model (SHASSAM) to selectivity. The two datasets were best fitted by different selection curves with a gamma selection curve providing the best fit to the 2000-2006 barramundi catch data and a lognormal selection curve for the 1891-1984 dataset. The difference in the optimum length of capture across the range of mesh sizes between these two selection curves ranged from 20 to 40 mm. However, the optimum lengths of capture for are substantially larger than reported previously for gillnet selectivity of barramundi in Fly River (Milton et al.1998). A thorough investigation of net selectivity characteristics for barramundi would require rigorous experimental design to account for factors other than mesh size including hanging ratio, filament gauge and fishing intensity and to assess entangling effects. Additional investigation is also required to investigate the relationship between contact selection and population selection to ensure appropriate catch size structure adjustment for stock assessment.