POPULATION-DYNAMICS OF JUVENILE TIGER PRAWNS PENAEUS-ESCULENTUS IN SOUTH QUEENSLAND, AUSTRALIA

A 2 yr study of the prawn population on a south Queensland seagrass be d between September 1988 and September 1990 provided information on th e 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 b etween September and July; peaks in the settlement occurred from Septe mber to November and February to March, Carapace length-frequency anal ysis was used to estimate the rates of growth and mortality of these c ohorts. Growth of P. esculentus juveniles was strongly influenced by w ater temperature. Growth rates increased from 0.03 to 2.1 mm CL wk(-1) with increasing temperature and can be described by the equation: GR = 0.00044e(0.317) where GR = growth rate (mm CL wk(-1)) and T = water temperature (degrees 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 summ er (December to February) tended to have higher mortality rates. Overa ll, the mortality rates were lower than reported for other species of Penaeus and this was attributed to little fish predation due to the lo w natural density of P. esculentus and the lush seagrass cover in this area. As the mortality rates appear to be independent of water temper ature and relatively low, the production of adult P. esculentus in the Moreton Bay fishery will be strongly influenced by the number and siz e of cohorts of juveniles settling in the nursery areas and their grow th.