Effects of Change in Catchability on Sampling of Juvenile and Adolescent Banana Prawns, Penaeus merguiensis de Man

Abstract

To provide the information necessary for optimizing sampling strategies, the effects of tidal, diurnal, lunar and seasonal cycles on the catchability of juvenile and adolescent banana prawns, P. merguiensis, were examined in the Norman River and in the inshore coastal zone of the Gulf of Carpentaria. A major part of the large variability in catches in both environments was attributable to marked tidal periodicity in catchability. In the river, large catches of juvenile P. merguiensis were taken only at or near the time of low water during both the neap and spring tide periods. Smaller prawns (< 12 mm carapace length) tended to be even more restricted to the time of low water than were larger prawns. This phase shift in catchability of larger prawns was particularly evident in the offshore sampling where large catches of adolescent prawns were made only at high water. Both the number and size of prawns caught also varied considerably with water depth. The reasons for the marked differences in catchability throughout a tidal cycle are not clear, but it is obvious that sampling can be restricted in time, thus providing much more consistent data with a minimum of effort.