Estimating gill-net selectivity for five species caught in the South East Fishery, Australia

Abstract

A formal approach to estimating selectivity patterns that allows for variability additional to Poisson sampling variability is outlined. This approach, which involves assuming that the catch of fish by a particular size of gill-net in a given size-class is distributed according to a negative binomial distribution, is applied to data for five of the species caught by experimental gill-nets in Australia’s South East Fishery. The data for two of these species (blue warehou and dogfish) are not compatible with the conventional assumption that the size of fish corresponding to maximum selectivity is linearly proportional to mesh size. Selectivity and population size-structure are found to depend on depth and habitat type for some of the species. It is necessary therefore to target future experiments to depth zones/habitat types in which the bulk of the catch is taken to estimate selectivity patterns for use in stock assessments.