periods of least abundance. Joyce (1965) con- 

 cluded that in northeast Florida juveniles first ap- 

 pear in the nursei-y grounds in early May, or prob- 

 ably earlier; their niunber increases considerably 

 in June to reach a maximum in July. In August, 

 as subadults, they migrate toward the sea, few re- 

 main in September and October, and almost none 

 from November to March. In North Carolina, Wil- 

 liams (1955a, 1959) found juveniles from mid- 

 April throughout the summer [to November, ac- 

 cording to a graph in his 1955a publication] ; peak 

 abimdanc« was in the first half of May. The in- 

 formation above strongly suggests that in the 

 brackish waters of North Carolina to northeast 

 Florida juveniles appear in large numbers in 

 April, reach a peak of abundance during the iDeriod 

 May through July, and their numbei's decline from 

 August through October. 



Brown shrimp leave inshore waters at different 

 sizes. Copel and (1965) reported that brown shrimp 

 move out to sea at 70 to 80 mm. t.l. Sampling by 

 Joyce ( 1965) , in turn, indicated that brown shrimp 

 emigrate offshore at an average size 100 to 105 

 mm. t.l. Recently, Trent (1967) reported that the 

 length of shrimp leaving the estuaries ranges from 

 60 to 130 mm. t.l., and that the size of those mov- 

 ing out of Galveston Bay, Tex., in 1966 increased 

 as the season of emigration progressed. 



Evidence is strong that shrimp migrate from in- 

 shore waters to sea during ebb tides. Copeland 

 (1965) reported peak abundance of shrimp leav- 

 ing through Aransas Pass, Tex., inlet on the ebb 

 tide and usually during the full moon. 



Information on migrations of brown shrimp 

 after tliey leave estuaries is rather meager. Mark- 

 recapture experiments by Klima (1964) indicated 

 that in Texas most individuals moved i>aral]el to 

 the coast and remained within 48 km. of the release 

 site in waters 16 to 30 fm. deep. In Texas and 

 Louisiana, a large proportion of the marked small 

 shrimp were reco\-ered also within 48 km. of the 

 release area. One individual, however, was caught 

 about 314 km. away, the longest distance known to 

 have been traveled by a brown shrimp. Studies by 

 Klima and Benigno (1965) suggested that along 

 the Mississippi Coast shrimp did not move great 

 distances from the release site, at least during the 

 summer ; the most rapid migration observed was at 

 a rate of 4.32 km. per day. These experiments, as 

 well as a previous one by Inglis (1960), also indi- 

 cate that at least part of the annually recruited 

 population in the northern Gulf moves from east 



to west. There are also indications that brown, 

 like white shrimp, migi-ate southward along the 

 northeast coast of Mexico, from late summer 

 through winter. This movement was first suggested 

 by Gunter (1962c), who pointed out that the 

 average monthly production from Texas waters 

 suggested a southward drift, and later Klima and 

 Benigno (1965) found that some of the shrimp 

 marked off Port. Aransas, Tex., in August moved 

 south; one individual traveled 104 km. in a south- 

 erly direction. 



Along the Atlantic Coast of the United States 

 some brown shrimp move northward during the 

 summer, apparently from the northernmost 

 spawning grounds off North Carolma. In the lower 

 portion of Chesajjeake Bay juveniles and subadults 

 are caught during summer and fall; information 

 gathered from different laboratories suggests that 

 only occasionally do brown shrimp move farther 

 north along the coast. Such a movement seems to 

 have taken place during the sampling reported 

 by Burkenroad (1939) in Delaware Bay and south- 

 ern New Jersey. Brown shrimp were first taken at 

 the end of August (minimum of 13 mm. c.l. in 

 males and 17 mm. c.l. in females), and they were 

 no longer there at the end of October. Because no 

 small juveniles were collected through the sam- 

 pling period and because 2 months before shrimp 

 arrived the water had reached higher tempera- 

 tures than were registered when they were pre- 

 sumably leaving the area, Burkenroad con- 

 cluded that juveniles had migrated from southern 

 waters where spawning and larval development 

 occurred. Small individuals have l^een caught as 

 far north as southern Martha's Vineyard, Mass., 

 but the small numter of records strongly sug- 

 gests that only rarely do stragglers reach that M 

 latitude. As a result of their mark-recapture 1 

 experiment in North Carolina, McCoy and Brown 

 (1967) stated that brown shrimp lea^nng Beaufort 

 Inlet moved southward from June through Octo- 

 ber. The record migration was about 241 km. in 

 5 weeks. 



EFFECTS OF TEMPERATURE 



Temperature greatly influences survival and 

 growth of brown shrimp. Laboratory experiments 

 by Zein-Eldin and Aldrich (1965) indicated that 

 postlarvae can tolerate wide fluctuations in tem- 

 perature and salinities, but are adversely affect«d 

 by extreme temperatures. Postlarvae survived tem- 

 peratures from 11° C. to 30° C, at salinities of 21 



544 



U.S. FISH AND WILDLIFE SERVICE 



