MEPS 135:43-55 (1996)  -  doi:10.3354/meps135043

We studied the 2-weekly, seasonal and annual variation in abundance of postlarval and juvenile Penaeussemisulcatus on a seagrass and an algal bed in the Embley River, Australia, from September 1986 to May 1992. The climate in this region is dominated by the wet and dry seasons, which lead to clear seasonal patterns of salinity, temperature and mean sea level in the estuaries. Similarly, catches of postlarvae entering the estuary and of postlarvae and juveniles in the estuary showed strong seasonal variation; they were highest just before and during the wet season, from September to April each year. Catch rates often had a bimodal distribution each year, but the relative size of each recruitment peak varied considerably between years. Long-term sampling over several years is clearly necessary to identify seasonal patterns in abundance and the range of variation in these patterns for juvenile penaeids. Total catches also varied substantially between years. The bimodal juvenile catch distribution suggests that recruitment to the offshore adult fishery should occur over 2 periods during the year. This is in contrast to previous work on adult P.semisulcatus in the Gulf of Carpentaria, which found only 1 period of recruitment and has important implications for the management of the fishery. Using multiple regression analysis, the most significant factor in determining the abundance of juvenile P.semisulcatus in the estuary was the number of benthic postlarvae that settled on the seagrass and algal beds. Rainfall was the most important environmental variable in the postlarval catch models. Increased rainfall was associated with a lower catch of postlarvae at the seagrass and algal sites but its major influence was through reducing the amount of algal habitat during the wet season. The mean sea level, or the amount of time that the seagrass bed was exposed, was also significant in the regression models for benthic postlarval and juvenile catches; increased exposure of the seagrass bed was associated with decreased catches of P.semisulcatus. However, because the proportion of juvenile catch variation explained by environmental variables was low, it is unlikely that predictive models of adult catches can be developed based on environmental factors acting on the estuarine stages of the life cycle of this species.

Penaeid . Postlarvae . Juvenile . Environment . Season . Annual variation . Seagrass . Algae