or some inherent character difference. An 

 experiment tested two of these factors-- 

 c rowdmg and container size. For test con- 

 tainers we used beakers of three sizes--l, 2, 

 and 4 liters. Four population densities were 

 tested at each capacity-- 1, 5, 10, and 20 

 shrimp. The experimental period was 28 days 

 at a temperature of 26° C. and salinity of 

 2 3 p.p.t. At the end of 28 days all animals 

 were weighed and measured. Population size 

 had little effect on growth for a given 

 volume of water. Growth increased, how- 

 ever, as beaker size increased, except for 

 beakers with one animal. Best growth was 

 in the 4-liter beaker with five animals. 

 These shrimp had an average growth rate 

 of 1.11 mm. per day during the 28-day test 

 period. 



In the past we have grown shrimp in either 

 4- or 45-liter aquaria. We suspected that 

 growth rate of postlarval shrimp reared in the 

 two sizes of aquaria was different even when 

 the number of animals per volume of water 

 was the same. To test this possibility, we held 

 postlarval brown shrimp from the same popu- 

 lation in the two tanks for 1 month at 25° C. and 

 31° C. Animals in the large tanks were ob- 

 viously larger within 2 weeks at both tempera- 

 tures. At the end of the experiment, shrimp in 

 both sizes of aquaria at the higher temperature 

 and in the large aquarium at the lower tem- 

 perature were roughly the same size. Animals 

 in the small aquaria at the lower temperature 

 were considerably smaller than any of the 



others. In view of these annbiguous results we 

 need to repeat the experiment. 



A number of laboratory-hatched postlarval 

 pink shrimp, brown shrimp, and seabobs were 

 supplied by the Larval Shrimp Identification 

 and Culture Project. Growth rates of these 

 laboratory-reared shrimp during 28 days at 

 constant temperatures were very similar to 

 that of natural animals collected from the surf. 



At the request of the Shrimp Dynamics 

 Program, we tested the survival of postlarval 

 brown shrinnp exposed to low temperatures. 

 This information is needed as a guide in field 

 sampling for abundance of postlarvae arriving 

 in the nursery area after the coldest part of 

 winter. Two studies were made covering the 

 same temperature range (2° to 8° C.). Post- 

 larval shrimp in the first experiment were 

 collected from 11° C. water Eind exposed up to 

 72 hours to these temperatures (a control 

 group was kept at 18° C.). Shrimp in the second 

 study were collected from 21° C. water. No 

 postlarvae in either experiment survived 24 

 hours of exposure to 2° C. 



Survival was lower at both 4° and 6° C. in the 

 second experiment than at 5° C. in the first. 

 This difference may be the effect of natural 

 acclimation of the first group of shrimp 

 to cooler water prior to study in the labora- 

 tory. Survival at 8° suid 18° C. was almost 

 100 percent for 72 hours in both experi- 

 ments. 



George W. Griffith, Project Leader 



GULF OCEANOGRAPHY PROGRAAA 



A program was initiated in 1965 to describe 

 the ocesuiographic environment of the Gulf of 

 Mexico. The funds provided were modest but 

 sufficient to allow some compilation of his- 

 torical data. The purposes of the program are 

 to: (1) define the water masses and subunits, 

 and their variations; (2) enumerate those 

 atmospheric amd oceanographic factors that 

 produce variations and modifications of the 

 waters; (3) determine the range of the varia- 

 tions and modifications in time and space; and 

 (4) combine these evaluations into practical 

 techniques of forecasting oceanographic condi- 

 tions in the fishing waters of the Gulf of 

 Mexico. 



THE AIR OVER THE GULF 



An examination of the atmospheric climate 

 over the Gulf was begun to learn the long- 

 period, ocean-atmosphere response. Although 



significant water-temperature data are not yet 

 available from the Gulf and Caribbean Sea, a 

 degree of correlation can be realized through 

 data from the North Atlantic Ocean. This study 

 is coordinated with a program at the See- 

 wetteramt, Deutscher Wetterdienst (German 

 Weather Service), in Hamburg, Germany, 

 whereby detailed evaluations are made of the 

 water temperatures and their anomalies in 

 the North Atlantic Ocean. The North Atlantic 

 ocean-atmospheric link is becoming clearer, 

 but the links in the Caribbean, Gulf, and 

 between these areas and the Atlantic are 

 extremely ill defined. 



A distinct cooling trend in the northern 

 Gulf began in 1958. This "deterioration" con- 

 tinued through 1964, and during these 6 years 

 mean annual temperatures were as much as 

 2.5° C. below normal (at Mobile in 1958; at 

 New Orleans in 1964). This cool period is the 

 longest experienced in the northern Gulf since 

 1906 when a 9-year "cold spell" ended. 



33 



