Estimation of catch rate and mean weight in the exploratory Dissostichus fisheries across Divisions 58.4.1 and 58.4.2 using generalised additive models

The exploratory longline fisheries in Divisions 58.4.1 and 58.4.2 (primarily targeting D. mawsoni) have been operating since 2003. Formal stock assessments have yet to be developed for these fisheries. Analyses of C2 catch rate and mean weight data from 2484 longline hauls conducted between 2003 and 2011 enabled the development of generalised additive mixed models that were then used to make predictions of catch rate and mean weight across fishable depths in both Divisions. Catch rates across the region are low compared to those in other Dissostichus fisheries within the Convention Area, with most locations within fishable depths predicted to have catch rate of less than 100 kg per 1000 hooks. The region around Prydz Bay is predicted have the highest catch rate of D. mawsoni and is also shown to be an important area for pre-adult D. mawsoni. Development of similar models to analyse fishery potential and population structure in other exploratory fisheries is recommended.