A comparison of fish bycatch communities between areas open and closed to prawn trawling in an Australian tropical fishery

Abstract

Abstract The bycatch fish community was compared between areas open and closed to prawn trawling in Australia's Northern Prawn Fishery to investigate the impacts of the fishery. Two regions of a large (∼6648 km2) closure were compared, with three areas in each region, one closed to trawling (Closed) and two open to trawling, one near the closure (Near) and one farther from the closure (Far). Sampling was undertaken both day and night. The two regions and two times were analysed separately using both multivariate and univariate analyses to examine changes in overall community structure and differences in individual species. Overall the results were equivocal with respect to the impact of trawling. The multivariate and univariate analyses showed that in both regions, during both day and night, the bycatch fish community of the Far open area differed from the Near and Closed areas, while the latter were similar. This at least partly reflected differences in depth and sediment. For individual species, most showed no significant difference between the areas open and closed to trawling. Of the significant results there was no consistent tendency for species to be more likely to occur inside the closure or be at a higher density or larger size within the closure. Benthic and demersal species, those more susceptible to capture by prawn trawls, were not consistently less likely to occur or at a lower biomass in the open areas. The lack of a strong contrast in the fish community between the open and closed areas is probably due to the comparatively low effort in the fishery, the highly aggregated nature of the trawling and the fact the fishery does not target the bycatch species. These factors may reduce the potential impact of trawling on the fish bycatch.