collected in 1962 and 1963 has been con-i- 

 pleted, and the catch data and related hydro- 

 graphic records are being transposed for 

 automatic data processing and future analysis. 

 In addition, about 500 plankton samples col- 

 lected from January to September 1964 were 

 examined as well as 300 plankton and bottom 

 s amples collected during overwintering studies 

 of postlarval brown shrimp. 



Distribution and Abundance, 

 January-September 1964 



Seasonal distribution of planktonic stages of 

 Penaeus spp. shrimp during the first 9 months 

 of 1964 closely resembled that in 1962 and 

 1963. Between January and April, planktonic 

 stages of Penaeus spp. occurred in three 

 general areas--(l) the waters off Corpus 

 Christi, Tex., (2) between Freeport, Tex., amd 

 Cameron, La., and (3) to the east off Morgan 

 City, La. After April, however, distribution 

 became more widespread, particularly shore- 

 ward of the 27 -m. depth. Catches were rela- 

 tively light xintil May but increased steadily 

 through September. Greater concentrations of 

 planktonic stages occurred at 27 to 46 m. than 

 in either the 7- to 13-nn. or 73- to 110-m. 

 depth zones. In addition, young shrimp were 

 about five tinnes more abundant in Texas 

 waters than in Louisiana waters (fig. 1). 

 Catches were particularly high in the 27-m. 

 zone south of Galveston. Typically, these 

 waters from 27 to 46 m. deep have produced 

 the greatest numbers of larvae each year 

 since 1962. 



As in the past, seasonal differences in catch 

 composition were evident. Postlarval stages 

 made up about 80 percent of the catch between 

 January and April. In the ensuing months, 

 however, the catch included predominantly 

 nauplial and protozoeal stages. Spawning in- 

 tensity, indicated by the percentage of nauplial 

 and protozoeal stages in the catch, was low 

 during January- April but increased slightly in 

 May and Jxine and sharply in August and 

 September. 



The timing of larval abundance varied with 

 depth (fig. 2). Penaeus spp. larvae were 

 abundant between June and September in 7 to 

 13 m. In 27 to 46 m., where most larvae 

 were caught, a small peak in May was followed 

 by a sharp increase in abundance during 

 August and September. Larvae occurred in 

 plankton hauls throughout the 9-month period 

 in 73 to 110 m. but were most abundant during 

 September. 



Overwintering 



Four cruises were made in waters off 

 Galveston between December 1965 auid Feb- 

 ruary 1966 to locate bottom concentrations of 

 postlarval brown shrimp. Samples were col- 

 lected in the water column with the Gulf-V 



50r- 



o 



o 

 a: 

 1 

 o 



2 



3 



150 r- 



73-110 METERS 



125 



50 



25 - 



JAN. 



MAR. 



Figure 2. — Seasonal abundance of Penaeus spp. larvae In 

 Texas and Louisiana waters during the first 9 months 

 of 1964. 



and Clarke-Bumpus plankton nets ^ aind along 

 the substrate by a newly designed bottom 

 sled (fig. 3). Station depths ranged from 5 to 

 37 m. but most sampling was inside 14 m. 



The major purpose of this study was to 

 determine if postlarvae of brown shrimp 

 leave the water column and burrow into the 

 substrate when temperatures fall below 16° C. 

 As expected, relatively cold water tempera- 

 tures (mean, 13.4° C.) prevailed during 

 December-February. In the initial cruises, 

 few postlarvae were taken and most of them 

 were on bottom rather than in the water 

 column. In later cruises, particularly at5-m. 

 stations where the postlarvae appeared to be 

 concentrated, large numbers occurred attem- 

 peratures as low as 10° C. on bottom as well 



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