Seasonal distribution and relative abundance of planktonic stage shrimp (Penaeus spp.) in the Northwestern Gulf of Mexico, 1961.

Planktonic stages of shrimp (Penaeus spp.) were sampled systematically in the Gulf of Mexico near Galveston, Tex., during January-December 1961. The Gulf-V plankton net was used every 3 weeks at stations established at water depths of 14, 27, 46, and 82 m. The study area encompassed about 20,725 km2. Trends in seasonal abundance of larvae varied with depth. At 14-m stations a unimodal trend was observed, and peak abundance was during May to September. In deeper waters a bimodal trend was apparent; peak abundance extended from late summer through fall. At all depths, trends in larval abundance increased as bottom water temperatures increased. Postlarvae were taken in plankton tows during January to April but were most abundant during August to December. Distinct shifts in the areal distribution of larvae and postlarvae were apparent. During January to March, larvae were restricted to water deeper than 14 m and shallower than 82 m whereas postlarvae occurred in all depths. This situation was generally reversed in April to August, when larvae were at all depths, but the distribution of postlarvae was restricted. In September to December, distribution patterns of larvae and postlarvae were generally similar. On the basis of this study and laboratory experiments on larval development and postlarval growth rates as affected by temperature, support is given to the premise that brown shrimp larvae or postlarvae, or both, overwinter in waters over the Continental Shelf.