SEASONAL OCCURRENCE AND SIZE DISTRIBUTION OF POST LARVAL 

 BROWN AND WHITE SHRIMP NEAR GALVESTON, TEXAS, WITH 

 NOTES ON SPECIES IDENTIFICATION ' 



By KE>fNETH N. Baxter and William C. Renfro% Fishery Biologist, (Research) 

 Bureau of Commercial Fisheries Biological Laboratory, Galveston, Tex. 77552 



Postlarvae of the genus Penaeus were collected at 

 the entrance to Galveston Bay, Tex., over a 4-year period 

 and along Galveston Island's beach during a I-year 

 period. Postlarval brown shrimp, P. aztecus, and white 

 shrimp, P. setiferus, were the predominant penaeids 

 caught. Morphological characters, seasonal size differ- 

 ences, and occurrence of juveniles in adjacent nursery 



ABSTRACT 



areas were used to identify these species. Seasonal 

 occurrence, size distribution, and measures of relative 

 abundance are given for postlarvae of the two species. 

 The uniformity in size of postlarvae from collections 

 along the beach and at the bay entrance indicated 

 that small shrimp do not grow much when they are 

 along the beach. 



Shrimp are the most vahiable marine fishery re- 

 source of the Gulf of Mexico, where commercial 

 landings annually exceed 170 million pounds and 

 are valued at nearly .ffiO million. Many aspects of 

 the biology and early life history of these crustaceans 

 have been examined; however, the factors causing 

 fluctuations in their abundance must be better de- 

 fined before optimum management of the shrimp 

 fishery can be realized. 



The early life histories of commercially important 

 species of the genus Penaeus inhabiting the north- 

 western Gulf of Mexico are similar. Each spawns in 

 offshore waters, where the planktonic larvae hatch 

 after several hours. During ensuing weeks, the 

 larvae pass through a series of metamorphoses and 

 reach near-shore areas as postlarvae. The young 

 shrimp grow rapidly after moving into estuarine 

 nursery areas, and return to offshore waters to com- 

 plete their life cycle. 



As Bearden (1961) has pointed out, the postlarvae 

 that reach inshore waters represent the success of 



' Contribution No. 212, Bureau of Comniercial Fisheries Biologica 

 Laboratory, CJalveston, Tex. 



= Present address: Department of Oceanograpiiy, Orecon State Univer- 

 sity, Corvallis, Greg. 



Note. — .Approved for publication .\pril 28, 1966. 



the spawning season and, after several months of 

 growth, will make up the bulk of the commercial 

 shrimp catch for a given year. Baxter (1963) has 

 shown that .systematic sampling of postlarvae enter- 

 ing the major nursery areas can provide an index 

 that is useful for predicting the subsequent abun- 

 dance of juvenile and adult shrimp on inshore and 

 offshore fishing grounds. 



The objectives of this report are to describe trends 

 in the seasonal abundance and size composition of 

 commercial shrimp postlarvae near Galveston 

 Island, and to evaluate the u.se of seasonal differences 

 in their body lengths as an aid in identifying the 

 various species. Also examined is the question : Do 

 young shrimp use the surf zone as a nursery area? 

 The results of this 4-ycar study form a basis for cur- 

 rent research on the biology and dynamics of the 

 postlarval pha.se of commercial shrimp populations 

 in the Gulf of Mexico. 



SAMPLING PROCEDURE 



Studies of postlarval shiimp began as part of a 

 developing investigation of the life history of penaeid 

 shrimp outlined in detail by Kutkuhn (1963). 

 Knowing that shrimp reach shore as postlarvae and 



FISHERY bulletin: VOLUME 06, NO. 1 



149 



