Results of long-term, seasonal 

 sampling for Penaeus postlarvae 

 at Breach Inlet, South Carolina 



Lawrence B. DeLancey 

 James E. Jenkins 

 J. David Whitaker 



South Carolina Wildlife and Marine Resources Department 

 PO Box 12559, Charleston. South Carolina 29412 



Recruitment of postlarvae of com- 

 mercially important penaeid 

 shrimp has been studied in several 

 areas in the southeastern United 

 States, e.g. on the Atlantic coast 

 (Bearden, 1961; Williams and 

 Deubler, 1968; Williams, 1969; 

 Allen et al., 1980) and the Gulf of 

 Mexico (Baxter, 1963; George, 1962; 

 Loesch, 1965; Christmas et al., 

 1966; Baxter and Renfro, 1967; 

 Caillouet et al., 1968, 1970; Ford 

 and St. Amant, 1971). Findings 

 from these studies indicate that 

 postlarvae are generally concen- 

 trated near oceanic inlets, different 

 species are abundant at different 

 times of the year, ingress through 

 inlets into estuarine nursery areas 

 is often influenced by factors such 

 as tide and time of day, and corre- 

 lations between number of post- 

 larvae and subsequent commercial 

 landings is often poor. 



In South Carolina most pub- 

 lished studies have examined post- 

 larval recruitment over a one- to 

 two-year period (Bearden, 1961; 

 Olmi, 1986; Wenner and Beatty, 

 1993). Long-term sampling was 

 conducted by Lunz 1 at several 

 coastal sites in South Carolina in 

 an effort to predict subsequent com- 

 mercial harvest. As an extension of 

 this work, long-term, seasonal sam- 

 pling was conducted at a single site 

 near Charleston, South Carolina, to 

 determine relative abundance and 

 timing of recruitment of Penaeus 



postlarvae. This study is part of a 

 continuing effort to relate postlar- 

 val abundance to subsequent land- 

 ings and to evaluate spawning suc- 

 cess of parental stocks. 



Materials and methods 



Samples were collected with a 1-m 

 diameter, 500-um mesh plankton 

 net fitted with a flowmeter at 

 Breach Inlet, South Carolina (be- 

 tween Sullivan's Island and the Isle 

 of Palms), from January 1975 to 

 August 1992 (Fig. 1). Breach Inlet 

 is an oceanic inlet with high veloc- 

 ity tidal currents (up to 150 cm/sec 

 flow). The tides in South Carolina 

 are semidiurnal and have an aver- 

 age range of tidal height of approxi- 

 mately 2 m between mean low wa- 

 ter and mean high water. Breach 

 Inlet was chosen as a site for in- 

 tensive monitoring of recruitment 

 because of its accessibility (boats 

 are not required for sampling and 

 it can be sampled in inclement 

 weather). Preliminary studies have 

 shown that postlarvae can be col- 

 lected in consistently high numbers 

 (several hundred per sample) at 

 Breach Inlet, and catches are com- 

 parable to collections made in other 

 estuaries in South Carolina (J. 

 Whitaker, unpubl. data). 



The net was deployed from a 

 bridge over the inlet and fished near 

 the bottom (approx. 10 m depth) for 



two one-hour periods during day- 

 light flood tides. Prior to 1978, 

 paired samples were taken twice 

 weekly (approximately 30 minutes 

 elapsed between samples). This ef- 

 fort was greatly reduced when 

 abundance of postlarval brown 

 shrimp, Penaeus aztecus, could not 

 be correlated with commercial 

 landings. After 1977, regular sam- 

 pling involved collecting two un- 

 paired samples per tide at one or 

 two week intervals from late Janu- 

 ary to early August. Hydrographic 

 information, including water tem- 

 perature and salinity, were also col- 

 lected during sampling (Table 1). 



In addition to bottom daylight 

 samples, consecutive samples were 

 taken over a full tidal cycle during 

 day and night (two surface and two 

 bottom samples per tide) in some 

 years during periods of high abun- 

 dance to examine possible influ- 

 ences of tide, time of day, and loca- 

 tion of the net on postlarval catch 

 rates. Consecutive samples of P. 

 aztecus were collected on 12-13 

 March 1975, 26-27 February and 

 30-31 March 1976, 17-18 March 

 1977, 24-25 February and 10-11 

 March 1983, 2-3 March and 2-3 

 April 1985, and 21 February and 

 3-4 March 1986 (flood tide only in 

 1986). Consecutive samples for P. 

 setiferus were collected on 9-10 

 June and 16-17 July 1975, 27-28 

 May and 28-29 June 1976, 9-10 

 June 1983, and 29-30 May 1989 

 (flood tide only in 1989). 



Plankton samples were pre- 

 served in 10% buffered formalin- 

 seawater and sorted in the labora- 

 tory. Postlarvae were sorted to spe- 

 cies in most instances by using 

 characteristics identified by Pear- 

 son (1939), Williams (1959), and 



Contribution 335 of the South Carolina Ma- 

 rine Resources Center. 

 1 Lunz, G. R. 1965. Annual report 1963-64, 



Bears Bluff Laboratories. Contrib. Bears 



Bluff Lab. No. 41. 10 p. 



Manuscript accepted 6 January 1994. 

 Fishery Bulletin 92:633-640 ( 1994). 



633 



