Factors affecting the distribution of commercially exploited penaeid prawns (shrimp) (Decapod:Penaeidae) across the northern Great Barrier Reef, Australia

In the far northern Great Barrier Reef, Australia, the spatial distribution of commercially important penaeid prawns (shrimp) can be coarsely differentiated by a combination of three factors; water depth, mud content of the sediment, and seafloor rugosity. Penaeus esculentus (brown tiger prawn) was associated with high mud content sediments of the inshore reef lagoon. Melicertus longistylus (red spot king prawn) was associated with the coralline sand sediments of the reef–shoal matrix, and Metapenaeus endeavouri (true endeavour prawn) straddled both sediment and bottom types but was concentrated over the inshore mud to mud–sand sediments. Melicertus latisulcatus (western king prawn) occurred in small numbers concentrated on pockets of terrigenous silica sand, close to the shoreline. Apart from these silica sand pockets, cross-shelf surficial sediment were dominated by the sand fraction (>0.063 mm particle size), high in CaCO3 (>80%) and were mainly biogenic in origin, except for a band of terrigenous muddy sediment close to the coast. Seafloor topography followed similar zonation with the highest complexity in the reef–shoal matrix (rugosity index 11.24, fractal dimension D = 1.052), grading back to a flat mud–sand plain (rugosity index 3.88, fractal dimension D = 1.005) in the inner reef lagoon close to shore. Multi-dimensional Scaling (MDS) analysis indicated an “offshore” grouping of species that was associated with low mud and high rugosity, and an “inshore” grouping that tended towards the opposite combination. The currently accepted regression model for the distribution of penaeids in the Gulf of Carpentaria was modified to reflect this dual effect of the sediment and three-dimensional complexity of reef-associated habitats. The new model significantly improved the amount of variation explained in biomass estimates for P. esculentus, Melicertus longistylus, and Metapenaeus endeavouri, but not for Melicertus latisulcatus.