Population dynamics of juvenile tiger prawns Penaeus esculentus in south Queensland, Australia

Abstract

A 2 yr study of the prawn population on a south Queensland seagrass bed between September 1988 and September 1990 provided information on the settlement, emigration, growth and mortality of juvenile brown tiger prawns (= shrimp) Penaeus esculentus. Prawns were sampled with a beam trawl at 2 wk intervals. In 1988/89 and 1989/90 respectively, 10 and 9 cohorts of small juveniles (2 to 3 mm carapace length, CL) settled between September and July; peaks in the settlement occurred from September to November and February to March. Carapace length-frequency analysis was used to estimate the rates of growth and mortality of these cohorts. Growth of P esculentus juveniles was strongly influenced by water temperature. Growth rates increased from 0.03 to 2.1 mm CL wk-L with increasing temperature and can be described by the equation: GR = 0.00044e0 31Twhere GR = growth rate (mm CL wk-') and T = water temperature ("C). Weekly instantaneous natural mortality rates were estimated for a maximum of 10 wk after settlement and ranged from M = 0.06 to 0.29, or 5.8 to 25.2 %. Cohorts which settled in the summer (December to February) tended to have higher mortality rates. Overall, the mortality rates were lower than reported for other species of Penaeus and this was attributed to little fish predation due to the low natural density of P esculentus and the lush seagrass cover in t h s area. As the mortality rates appear to be independent of water temperature and relatively low, the production of adult l? esculentusin the Moreton Bay fishery vvlll be strongly influenced by the number and size of cohorts of juveniles settling in the nursery areas and their growth.