Sediment type as a factor in the distribution of commercial prawn species in the western Gulf of Carpentaria, Australia

Abstract

The relationship between sediment type and the distribution of the commercial prawn species of the western Gulf of Carpentaria was examined. The distribution of sediments was described on the basis of the mud content while the spatial distributions of the adult populations of all the commercial species were described from the results of trawl surveys. The main species caught were the tiger prawns Penaeus esculentus and P. semisulcatus, the endeavour prawns Metapenaeus endeavouri and M. ensis, and king prawns P. latisulcatus and P. longistylus, the banana prawn P. merguiensis, and the coral prawn Solenocera australiana. The individual species were caught in varying depth ranges and, in order to assess the influence of sediment type on the spatial distributions, a stepwise multiple regression analysis was carried out in which variation due to depth was considered before that due to percentage mud. Although depth generally accounted for most of the variation in catch-per-unit-effort (CPUE), percentage mud was also found to be a significant factor for all species except P. Merguiensis. Three species, P. semisulcatus, M. ensis and S. australiana, showed a preference for sediments with a high mud content while the abundances of P. esculentus, M. endeavouri and P. latisulcatus were each negatively correlated with percentage mud. P. longistylus showed a strong depth-mud interaction, being largely found on sediments of 40-60% mud in depths of 40-50 m. P. merguiensis was found in depths <20 m but, because the trawl stations in this depth range were all high in mud content, there was no significant correlation with sediment type. The distribution of the CPUE of all the commercial species combined was relatively even and showed no correlation with sediment type (either percentage mud or percentage organic carbon) and only 13% of the variation could be explained by a preferred depth range. Unlike the adults, juveniles were largely confined to shallow inshore waters (<20 m). Tagging experiments carried out on the major commercial species, P. esculentus and P. semisulcatus, in common inshore nursery grounds demonstrated the preferences for different sediment types; P. semisulcatus recaptures were mainly in areas with the finest sediments (>75% mud) whereas those of P. esculentus were associated with coarser sediments (50-75% mud).