south from near Beaufort. N.C., where it was 

 tagged, to the east coast of Florida, coveiing a dis- 

 tance of about 580 km. in 95 days. The longest 

 northward migration was made by a shrimi^ that 

 moved from south of Cape Kennedy, Fla., north to 

 the coast of South Carolina, a distance of about 

 419 km. in 168 days. 



McCoy and Brown (1967) also reported that 

 some shrimjD migrate southward from North Car- 

 olina. The greatest distance known to have been 

 traveled by the animals they released was 555 km. ; 

 two individuals were recaptured off St. Augustine, 

 Fla. That all of the North Carolina population 

 does not leave the area during the winter, how- 

 ever, is attested by the limited white shrimp fishery 

 off' Cape Fear during the coldest months of the 

 year (Williams, 1955a). 



The limited infonnation gathered by Lindner 

 and Anderson (1956) through tagging in the 

 northeastern Gulf indicated that during the fall 

 and winter white shrimp tend to move into deeper 

 water and toward the mouth of the Mississippi 

 River. The population from the northwestern 

 Gulf, west of the Mississippi River to central 

 Texas, also exhibits only offshore and inshore 

 movements associated with temperature changes 

 and spawning. The marine shelf off the mouth of 

 the Mississippi River seems to be a natural barrier 

 because this area was not crossed apparently in 

 either direction. 



Along the coast from south-central Texas to 

 northern Mexico, white shrimp seem to move south- 

 ward during the fall and early winter and north- 

 ward in the spring. These coastwise movements 

 compare with those observed for white shrimp on 

 the Atlantic Coast and were first documented by 

 Lindner and Anderson (1956) and later by Gunter 

 (1962c), who leased his conclusions on e\-idence 

 that catches of white shrimp increased during the 

 winter southward along the Coast. 



EFFECTS OF TEMPERATURE 



As stated earlier, spawning seems to be greatly 

 influenced l)y temperature, which by its sudden 

 changes apparently initiates and later tenninates 

 the o\T.ilation. Temple and Fischer (1967) foimd 

 that along the coast of Texas white shrimp larvae 

 were present from May through September and 

 that a close correlation appears to exist between 

 temperature and al)undance of larvae. 



The rate of growth is directly related to tem- 

 perature, for it reaches its maximum during the 



warmer months, becomes very slow or negligible 

 during winter, and resumes or increases with the 

 advent of higher temperatures in late winter or 

 early spring. 



Laboratory experiments by Zein-Eldin and Grif- 

 fith (1965) indicated that temperature affected the 

 growth and molting of i^ostlarvae. Animals tested 

 at 18°, 25°, and 32° C, at a salinity of 25 p.p.t., 

 showed that molting frequency and growth in- 

 creased with temperature, although the increase 

 in total length per molt was independent of tem- 

 perature. This finding suggests that temperature 

 influences growth through a change in molting rate 

 but has no effect on the increase in size per molting. 

 Their studies indicated further that, at a given 

 salinity, postlarval white shrimp are more sensi- 

 tive to low temperatures than are postlarval brown 

 shrimp, but that, conversely, white shrimp post- 

 larvae can better withstand high temperatures. 

 Another experiment by Zein-Eldin (1966) con- 

 firmed this result. 



Lindner and Anderson (1956) gathered evidence 

 that white shrimp moved from shallow to deeper 

 water during cold periods and that the smaller 

 shrimp returned to shallower water when the tem- 

 perature of the water increased. 



There is also some information on how extremes 

 of temperature affect white shrimp. Lunz (1956) 

 reported that P. setifcnis. 51 to 95 mm. t.l., had sur- 

 vived 36° C. in a pond in South Carolina. Reports 

 of mortality of white shrimp during cold waves 

 have been given by Gunter (1941), Gunter and 

 Hildebrand (1951), Lunz (1958), and Joyce 

 ( 1965) , all of whom have found white shrimp dead 

 after near freezing (4° and 4.5° C.) or freezing 

 temperatures. Joyce found shrimps in a state of 

 decay, which suggested that they had died during 

 the first days of freezing temperatures. Sudden 

 changes of temperature often may Ije responsible 

 for the mortality of the shrimp rather than the 

 temperature itself, although both the rate of 

 change and the duration of high or low tempera- 

 tures doubtlessly affect mortality. 



EFFECTS OF SALINITY 



Conclusions about the influence of salinity on 

 the life and distribution of white shrimp inshoi'e 

 vary widely. High concentrations of young indi- 

 viduals in low-salinity waters (less than 10 p.p.t.) 

 have been reported by a number of authors — 

 Gunter (1950), Gunter and Shell (1958), Gunter 

 (1961a), Gunter et al. (1964), and H. Loesch (in 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEVS 



48.5 



