Population structure of Thenus orientalis and T. indicus (Decapoda: Scyllaridae) in northeastern Australia

Abstract

[Extract] Bay lobsters of the genus Thenus are a valuable component of the incidental catch of the penaeid trawl fisheries of northern Australia. The 2 species present, Thenus indicus Leach, 1815 and Thenus orientalis (Lund, 1793), have mutually exclusive distributions. For each species, relative abundance, size and sex composition were measured monthly and related to physical characteristics including temperature, salinity, depth and sediment type. Both species populations were characterised by contagious distributions. Mean density of T. indicus was 1.78 (±0.15) lobsters ha⁻¹, while that of T. orientalis was 2.02(±0.13). In both populations, depth and sediment type were significantly correlated with abundance. T. indicus was most abundant in depths of 10-30 m and where sediments were characterised by a preponderance of find sands and silt. In contrast, T. orientalis was most abundant in 1.00 mm particle size. In both species, mean size varied significantly thorughout the year as a function of growth and recruitment. Male and female T. indicus were equally abundant, while male T. orientalis were significantly more abundant than females.