entirely of cropped filaments of blue-green algae 

 and such diatoms as ordinarily in the natural habi- 

 tat would have been found adhei-ent to them.'" 



Studies by Zein-Eldin (1964) emphasized the 

 importance of an abundance of food during the 

 postlarval-juvenile period in the life of the shrimp 

 and indicated the ultimate value of the estuarine 

 waters in providing the vast amount of food re- 

 quired for the rapid gro^vth of the shrimp before 

 it returned to the sea. 



SUBSTRATE 



P. setiferus inshore live mostly on muddy or 

 peaty bottoms that have large quantities of decay- 

 ing organic matter or vegetation for protection. 

 Occasionally they occur on bottoms of sand or clay 

 (Williams, 1955a, 1955b). Laboratory experiments 

 by Williams (1958) indicated that the young 

 white shrimp prefer softer substrates than do the 

 young pink or brown shrimps. 



Adult white shrimp are most abundant in off- 

 shore waters on soft muddy and silt bottoms. They 

 also live on bottoms of clay or sand with frag- 

 ments of shells (Springer and Bullis, 1954: Hilde- 

 brand, 1954, 1955). 



P. setiferus burrows in the bottom but appar- 

 ently not as regularly as do the brown or pink 

 shrimps. Williams (1958) observed that it leaves 

 the long antennae lying on the surface of the bot- 

 tom, whereas the other two shrimps often bury 

 their antennae (which are shorter than those of 

 the white shrimp). 



DIEL CYCLE 



Although P. setiferus has been thought to be a 

 diurnal species, Williams (1958) found that in the 

 laboratory it is also active at night. Fislung for 

 white shrimp, inshore as well as offshore, is usually 

 carried out during the day, but some successful 

 catches are made at night. Joyce (1965) considered 

 white shrimp to be diurnal, but stated that in cer- 

 tain inshore localities during the summer, sample 

 catches at night equaled or even exceeded those 

 made during the day. He suggested that migration 

 could have been a factor in the abundance of 

 shrimp in these instances. 



MOVEMENTS 



Most scientists believe that favorable currents 

 transport the larvae and early postlarvae toward 

 inshore waters. 



Many studies have been made on the movements 



of the postlarvae of white shrimp. As stated earlier, 

 shrimp reach the nui-sery grounds as jxtstlarvae, 

 6 to 7 mm. long (Weymouth et al., 1933 ; Anderson, 

 King, and Lindner, 1949 ; Bearden, 1961 ; Baxter 

 and Eenfro, 1967). There they adopt a bentliic 

 existence (Anderson, King, and Lindner, 1949; 

 Williams, 1955a) either immediately or, as indi- 

 cated by Joyce (1965), after having traveled some 

 distance inland. Williams (1955a) also stated that 

 postlarvae, as well as juveniles, are able to move 

 many miles before finding a suitable nursery area. 

 In the northern Gulf of Mexico they arrive in 

 coastal waters from May to November (Christmas 

 et al, 1966; Baxter and Renfro, 1967). According 

 to Baxter and Eenfro (1967), peak postlarval im- 

 migration into Galveston Bay, Tex., occurs in the 

 summer. In South Carolina (Bearden, 1961) and in 

 North Carolina (Williams. 1955a) postlarvae 

 begin to arrive in early June, and the period of in- 

 flux extends throughout the summer to mid- 

 August or September. Postlarval abundance ap- 

 pears to show two peaks in the area, one in early 

 June and the other in mid-August. 



In the nurse ly grounds, the size of juveniles 

 often shows a gradient ; the smaller individuals are 

 farther inland. "WHiite shrimp may be found in 

 rivers as far from the coast as about 160 km. 

 (Burkenroad, 1934) and 210 km. (Joyce, 1965) — 

 farther than the brown or pink shrimps. Shrimp 

 grow rapidly, and as they grow they move back 

 to water nearer the sea and shrimp return to the 

 sea when they have attained a modal length be- 

 tween 100 and 120 mm. t.l. (Weymouth et al., 1933 ; 

 Gunter, 1950; Lindner and Anderson, 1956). The 

 seaward migration takes place from spring 

 through summer and early winter. In some areas 

 two migrations are typical, one in spring and the 

 other at the onset of winter. The first seems to be 

 undertaken by shrimp hatched late in the previous 

 spawning season, and the second migration is by 

 shrimp spawned early in spring. Lindner and 

 Anderson (1956) and Joyce (1965) believe that 

 the stage of maturation of the gonads is the main 

 determinant of tliis migration, although fall and 

 winter temperatures also influence it. 



Adult shrimp may migrate long distances par- 

 allel to the shoreline. On the Atlantic Coast, the 

 tagging experiments by Lindner and Anderson 

 (1956) indicated that white shrimp move south 

 during the fall and early winter and northward in 

 late winter and early spring. The longest migra- 

 tion recorded was made by a shrimp that moved 



4S4 



U.S. FISH AND WILDLIFE SERVICE 



