Influence of oceanographic processes on the early life stages of the blue shrimp (Litopenaeus stylirostris) in the Upper Gulf of California

The possible relationship between circulation patterns and the recruitment of early stages of penaeid shrimp in the Upper Gulf of California was explored by collecting postlarvae (mesh size 0.505 mm) simultaneously in two locations, one off the coast of Sonora (Golfo de Santa Clara: 31°44′49 N–114°33′12 W) and the other off the Baja California peninsula (San Felipe: 31°11′8.3 N–114°53′13.9 W) during two complete fortnightly cycles (July 12–27, 1995 and June 30–July 16, 1996). Individuals with cephalothoracic length from 0.8 to 3.91 mm without a clear size-increasing pattern were found throughout the sampling period, suggesting continuous recruitment to the area. The circulation in the study area was simulated with a three-dimensional baroclinic model forced with tides and climatological hydrography at the mouth of the Gulf of California, and winds and heat and freshwater fluxes at the sea–air interface. Spawning stock surveys have shown that maximum concentration of mature females is near the coast of Sonora (mainland Mexico). The model predicts surface currents of about 8 cm s−1 and suggests that postlarvae found off the coast of the peninsula may come from a different reproductive unit than those found off the mainland coast. This may explain why postlarvae found in Golfo de Santa Clara (mainland) are larger (and, presumably, older) than those found in San Felipe (Baja California). Possible relationships among circulation patterns, lunar cycle, former Colorado River runoffs and time of spawning are discussed.