Comparative recruitment of the banana prawn, Penaeus merguiensis, in five estuaries of the south-eastern Gulf of Carpentaria, Australia

Recruitment patterns of postlarvae immigrating into mangrove nursery areas of five major estuaries around the south-eastern Gulf of Carpentaria, as well as juveniles emigrating offshore into coastal waters, were compared for the banana prawn, Penaeus merguiensis, from September 1978 to March 1979.. Although considerable variability was observed among rivers, some basic recruitment patterns were discernible. Recruitment of postlarvae tended to follow a 28-day cycle with increased immigration on alternate spring tides. Variability between rivers in the number of resident juvenile prawns at any one sampling time resulted mainly from differences in the relative magnitude of postlarval settlement from these monthly cohorts. After the first heavy rainfall of the monsoon season, the lower reaches of rivers with !xger catchment areas a!! ran fresh, setthg up a physica! barrier to further past larval immigration. In contrast, post larval immigration continued throughout the study period in the river with the smallest catchment. There was a trend for more successful immigration earlier in the more northern rivers. Offshore emigration was influenced by rainfall, tide height and number of resident juvenile prawns at the time of emigration. The relative importance of these three factors differed among rivers, depending on the timing of rainfall in relation to the timing of juvenile population changes and the degree of flooding. These local differences in the timing of emigration of juveniles could be detected in the abundance and size of adolescent prawns in the offshore coastal area of the south-eastern Gulf which in turn influenced the size composition of prawns available to the commercial fishery.