458 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



MISS. I ALA. GA 



"oe.LE,. \\ 



n lFlorida)/-— 



, . ^ ly^ — y\ST MARKS* 



NEW ORLEANS^^I^, * -^ ^^l.^-^^ 



r ' > -" SEPT.- MAR. 



CORPUS (/? '-ALL YEAR 



CMRISTlff^^N SEPT -DEC. 



'■SEPT-DEC. 



»,ATA»oRos GULF OF MEXICO 



SOTO LA MARINA 



Figure 70. — Small shrimp (up to 13 cm.) movements of 

 marked individuals. 



Figure 71. — Large shrimp (13 cm. and larger) spring 

 movements of marked individuals. 



PORT LAVACA 



?'GALVESTON,_ i 1 ? 



CORPUS _w/^ ~^ 



CHRisTiiT* SEPT -DEC. >^0C 



MISS. I ALA, (I GA 



UOBlLEp 



florida]/--- 



iST, MARKS, 



> "^ SEPT.- DEC. 



BROWNSVILLE 



GULF OF MEXICO 



*< Jtampico 



Figure 72. — Large shrimp (13 cm. and larger) fall and 

 winter movements of marked individuals. 



August or September spawning, both in Louisiana 

 and in Central Texas. The shrimp from the first 

 successful spawning have left the estuarine 

 nursery grounds by midwinter. The young from 

 the second successful spawning generally remain 

 during winter in the estuarine waters and the 

 immediately adjacent inner littoral waters. 



The growth of the shrimp is quite rapid during 

 the warm months of the year. From the time of 

 hatching until they reach a length of about 120 

 mm. the shrimp apparently increase at a rate that 

 averages more than a millimeter each day. This 

 rapid rate continues until about the end of October 

 when growth stops or almost stops, apparently 

 as a result of temperature changes. From about 

 the end of October until the end of February or of 

 March, depending upon the locality, there is 

 little or no growth. In the spring, as the water 

 temperature increases, the shrimp again resume 

 their rapid growth. 



From central Texas south there is a definite 

 possibility of migration. In the spring, based 

 upon specimens marked in Mexico, there is a 

 northward movement of shrimp. By inference, 

 and from the time of the first successful spawning, 

 but not based upon marked specimens, it appears 

 highly probable that shrimp from the central 

 and southern part of Texas may move south to 

 the coast of Mexico during the fall and early 

 winter, probably comparable to the movement 

 along the South Atlantic coast of the United 

 States. 



In the northern portion of the Gulf of Mexico 

 the wanderings of the shrimp can better be de- 

 scribed as movements rather than as migrations 

 (figs. 71, 72). The young gradually move from the 

 estuarine waters to those of the Gulf. Once in the 

 Gulf they appear to mill about like grazing cattle. 

 However, as the temperatures drop during winter 

 the shrimp tend to move a little farther offshore, 

 and as the waters warm in the spring they tend 

 to move back closer toward shore. 



The movements of the shrimp are associated 

 with spawning and with temperature. The normal 

 spawning movement is offshore. During winter, 

 in some localities, the movement becomes coast- 

 wise because of temperature gradients. Along 

 the northern part of the Gulf of Mexico, warmer 

 winter waters which the shrimp seek are generally 

 found in a belt between the 5- and 30-fathom lines. 



