376 



Abstract— We measured growth and 

 movements of individually marked 

 free-ranging juvenile white shrimp 

 [Litopenaeus setiferus) in tidal creek 

 subsystems of the Duplin River, 

 Sapelo Island. Georgia. Over a period 

 of two years, 15.974 juvenile shrimp 

 (40-80 mm TL) were marked inter- 

 nally with uniquely coded microwire 

 tags and released in the shallow upper 

 reaches of four salt marsh tidal creeks. 

 Subsequent samples were taken every 

 3-6 days from channel segments 

 arranged at 200-m intervals along 

 transects extending from the upper to 

 lower reach of each tidal creek. These 

 collections included 201,384 juvenile 

 shrimp, of which 184 were marked 

 recaptures. Recaptured shrimp were at 

 large an average of 3-4 weeks (range: 

 2-99 days) and were recovered a mean 

 distance of <0.4 km from where they 

 were initially marked. Mean residence 

 times in the creek subsystems ranged 

 from 15.2 to 25.5 days and were esti- 

 mated from exponential decay func- 

 tions describing the proportions of 

 marked individuals recaptured with 

 increasing days at large. Residence 

 time was not significantly correlated 

 with creek length (Pearson = -0.316, 

 P= 0.684 I, but there was suggestive 

 evidence of positive associations with 

 either intertidal (Pearson r = 0.867, 

 P=0.133) or subtidal (Pearson /-=0.946, 

 P=0.054) drainage area. Daily mean 

 specific growth rates averaged 

 0.009 to 0.013 among creeks; mean 

 absolute growth rates ranged from 

 0.56-0.84 mm/d, and were lower than 

 those previously reported for juvenile 

 penaeids in estuaries of the southeast- 

 ern United States. Mean individual 

 growth rates were not significantly 

 different between years (/-test, P>0.30) 

 but varied significantly during the 

 season, tending to be greater in July 

 than November. Growth rates were 

 size-dependent, and temporal changes 

 in size distributions rather than tem- 

 poral variation in physical environ- 

 mental factors may have accounted for 

 seasonal differences in growth. Growth 

 rates differed between creeks in 1999 

 U-test, P<0.015), but not in 1998 (r-test, 

 P>0.5). We suggest that spatial varia- 

 tion in landscape structure associated 

 with access to intertidal resources may 

 have accounted for this apparent inter- 

 annual difference in growth response. 



Manuscript approved for publication 

 30 September 2003 by Scientific Editor. 



Manuscript received 20 January 2004 

 at NMFS Scientific Publications Office. 



Fish. Bull. 102:376-388(20011. 



Individual growth rates and movement of 

 juvenile white shrimp (Litopenaeus setiferus) 

 in a tidal marsh nursery* 



Stacey Webb 



Florida Department of Environmental Protection 



Water Quality Standards and Special Proiects Program 



2600 Blair Stone Road, M.S. 3560 



Tallahassee, Floida 32399 



E-mail address: stacey fekervcudep state. fl. us 



Ronald T. Kneib 



UGA Marine Institute 

 Sapelo Island, Georgia 31327 



In 2001, shrimp became the most popu- 

 lar seafood in the United States when 

 per capita consumption (1.54 kg) sur- 

 passed that of canned tuna (1.32 kg) 

 for the first time in recorded history 

 (NOAA 1 ). Although 77% of the catch 

 is from the Gulf of Mexico, commercial 

 fisheries in Atlantic coastal states of 

 the southeastern United States also 

 depend heavily on penaeid shrimp pop- 

 ulations. Of the three most common 

 estuarine-dependent penaeid species 

 (Litopenaeus setiferus, Farfantepenaeus 

 aztecus, and F. duorarum) 2 harvested 

 in the South Atlantic Bight, white 

 shrimp Litopenaeus setiferus domi- 

 nate, comprising >70% of the catch in 

 the region (North Carolina to the east 

 coast of Florida) and 75-87% in South 

 Carolina and Georgia (NMFS :I ). 



Concerns over the possibility of de- 

 pleting the resource as early as the 

 1930s led to intensive studies of the 

 life cycle (Lindner and Anderson, 1956; 

 Williams, 1984). The white shrimp has 

 an annual life cycle that can be divid- 

 ed into offshore (oceanic) and inshore 

 (estuarine) phases. Adults spawn in 

 Atlantic waters in spring and the post- 

 larvae migrate into estuaries, aided by 

 flood tides and wind-generated currents 

 (Lindner and Anderson, 1956; Wenner 

 et al., 1998). Postlarvae penetrate into 

 the shallow upper reaches of the nurs- 

 ery habitat where juveniles achieve a 

 substantial portion of their adult body 

 mass before moving into deeper creeks, 

 rivers, and sounds where they approach 

 maturity and emigrate seaward to 



spawning areas (Muncy, 1984; Wil- 

 liams, 1984). 



Given the commercial importance 

 and early interest in this species, sur- 

 prisingly little research has focused on 

 the juvenile stages within tidal marsh 

 nursery habitats ( Minello and Zimmer- 

 man, 1985; Zein-Eldin and Renaud. 

 1986; Knudsen et al., 1996; McTigue 

 and Zimmerman, 1998). Seasonal mi- 

 grations and ontogenetic movements 

 of white shrimp between coastal ocean 

 spawning grounds and estuarine nurs- 

 eries are well known ( Dall et al.. 1990 1. 

 as are the sometimes extensive migra- 

 tions of adult shrimp along the Atlantic 

 coast, primarily to the south during 

 fall and early winter, and northward in 

 late winter and early spring (Lindner 

 and Anderson, 1956; Shipman, 1983). 

 Within the estuary, juvenile white 



■Contribution 921 of the Univerisity of 

 Georgia Marine Institute, Sapelo Island, 

 GA. 



1 NOAA (National Oceanic and Atmo- 

 spheric Administration. 2002. Shrim 

 p overtakes canned tuna as top U.S. sea- 

 food. Website: http://www.noaanews. 

 noaa.gov/stories/s970.htm. I Accessed: 

 28 August 2002.] 



- These species were all previously included 

 in the genus Penaeus, but the subgenera 

 were elevated to genera by Perez-Farfante 

 and Kensley (1997). 



:! NMFS (National Marine Fisheries 

 Service). 2002. Unpubl. data. Web- 

 site: http://www.st.nmfs.gov/stl/commer- 

 cial/index.html. lAccessed 29 August 

 2002.1 



