Species composition and distribution of commercial penaeid prawn catches in the Gulf of Carpentaria, Australia, in relation to depth and sediment type

To describe the distribution of the commercial penaeid species caught in the Gulf of Carpentaria, species composition data were drawn from studies conducted in the gulf between 1977 and 1992, supplemented with data from commercial catches monitored by fishers trained in species identification. The catch is made up of eight species in four commercial species groups. Three species account for most of the catch: the banana prawn Penaeus merguiensis (about 41%) and the tiger prawns P. esculentus (24%) and P. semisulcatus (23%). Three others, the endeavour prawns Metapenaeus endeavouri (8%) and M. ensis (3%) and the king prawn P. latisulcatus (1%), are found in commercial quantities but usually as incidental components of catches. Two species, the black tiger prawn, P. monodon, and the red-spot king prawn, P. longistylus, are caught only occasionally. At a fine spatial scale (six-nautical-mile grids), each species group was found to consist largely of just one species, and the ratio of one species to another within a species group were relatively stable over time. By using these ratios in combination with fishers' logbook data, it was possible to refine annual catch statistics for the gulf to the level of species rather than, as in the past, just to species group. The spatial distributions of individual species were found to be related to depth and/or sediment type. Catches of P. merguiensis were mainly from the eastern and southern gulf, and in waters shallower than 20 m, but were not associated with any particular sediment type. The brown tiger prawn, P. esculentus, was most abundant in the southern gulf and shallower parts of the western gulf (< 35 m deep). The sediments in these areas were sand or muddy sand. In contrast, the grooved tiger prawn, P. semisulcatus, was most abundant in the north-eastern gulf and the deeper parts of the western gulf (>35 m deep) where sediments were mud or sandy mud. The blue-tailed endeavour prawn, M. endeavouri, was the most widespread of the species in the gulf, but, like P. esculentus, it was most abundant in the south-eastern gulf and shallower parts of the western gulf, where sediments were either sand or muddy sand. The red endeavour prawn, M. ensis, was more limited in its distribution, with highest abundance in the north-eastern gulf and in the deeper parts of the western gulf (35-45 m). Here, the sediments were more than 60% mud.