Species composition and timing of penaeid shrimp postlarvae (Decapoda, Penaeidae) in two zones of the Mexican Pacific coast

The species composition and variation in density (postlarvae m−3) of penaeid shrimp postlarvae were surveyed every 14 days in two zones of the Mexican Pacific coast; in the north (Mazatlán, 23°N 106°W) and south (Gulf of Tehuantepec, 15°N 95°W). Sampling coincided with full moon and new moon, and they were carried out with plankton net (0.3 m mouth diameter and 450 μm mesh size). Average sea surface temperature (SST) for 1985-1995 increased from Mazatlán (26.2 ± 0.2°C) to Tehuantepec (28.3 ± 0.5°C). The difference in SST between the coldest and warmest month was 7.8°C in Mazatlán and 3.3°C in Tehuantepec. Four species of penaeid shrimp postlarvae were identified: Litopenaeus vannamei (Boone, 1931), L. stylirostris (Stimpson, 1874), Farfantepenaeus californiensis (Holmes, 1900) and F. brevirostris (Kingsley, 1878). There was a regional variation in the species composition. L. vannamei was abundant at both coasts with 40% and F. californiensis varied from south to north from 45 to 36%; the less representative species were L. stylirostris and F. brevirostris, which varied from south to north from 15 to 24%. The occurrence period near Mazatlán is seven months, and it is year-round in Tehuantepec. This study suggests that warm water and low seasonal SST variability facilitate the presence of the shrimp larvae over a longer period.