Recruitment of Postlarval and Juvenile Brown Shrimp (Penaeus aztecus Ives) from Offshore to Estuarine Waters of the Northwestern Gulf of Mexico

We use relatively rare continental shelf distribution and abundance data for postlarval brown shrimp, Penaeus aztecus Ives, along with marsh postlarval and juvenile data, to investigate recruitment to the Calcasieu River estuary in western Louisiana. Catches of postlarvae peaked in the offshore sampling in February and March, while catches in the marsh peaked in March. Densities of postlarvae collected offshore were greater in the shallowest nearshore depths. For the five years of collections in the marsh, the peak immigration period of late stage postlarvae and juveniles varied from the end of March to mid-May. Highest densities of postlarvae were taken at water temperatures of 12-18 °C for both offshore and marsh plankton collections. We relate the postlarval data and meteorological data on atmospheric cold-front passages, along with field and experimental data from the literature, to hypothesize a behaviorally-mediated transport mechanism for the enhancement of postlarval brown shrimp recruitment. The postulated mechanism utilizes the post-frontal return of southerly winds and northward flowing currents. In this model, postlarvae use cold-front associated changes in water temperature and salinity as environmental cues in combination with a diel activity cycle that puts them in contact with the bottom. This behaviour would facilitate the selection of the appropriate directional flow and could also facilitate the accumulation of postlarvae at the mouths of estuaries.