NOTE DeLancey et al.: Seasonal sampling of Penaeus postlarvae 



637 



(Williams and Deubler, 1968; Matthews et al., 1991 ). 

 Olmi ( 1986) in addition to collecting more P. aztecus 

 at night, also collected the majority of P. setiferus 

 postlarvae at night in a tidal creek in South Caro- 

 lina. These findings are in agreement with similar 

 studies in the Gulf of Mexico, where P. setiferus was 

 found to be more abundant near the surface at night 

 in an inlet (Duronslet et al., 1972) and over a tidal 

 flat (Caillouet et al. , 1968 ). Wenner and Beatty ( 1993 ) 

 collected 951 of all penaeid postlarvae at night (in- 

 cluding a collection at a creek adjacent to Breach 

 Inlet). In our study, no difference was detected be- 

 tween day and night catches off! setiferus, possibly 

 because we employed a larger net than in the other 

 studies conducted in South Carolina in a higher- 

 velocity tidal flow. This may have minimized avoid- 

 ance of the gear by postlarvae during daylight. Addi- 

 tional sampling may clarify these observations. 



Similar to observations made in our study, Olmi 

 ( 1986) generally collected fewer postlarvae during full 

 moon phases in South Carolina. Williams and 

 Deubler (1968) in North Carolina and Allen et al. 

 (1980) in the Florida Keys collected fewer P. duor- 

 arum at night during full moon phases than during 

 new moon phases. Perhaps high light levels at night 

 may delay ingress for several days, causing postlarvae 

 to remain on offshore substrates ( Matthews et al., 199 1 ). 



-0.5 



3.0 



<=i 2.5 

 CO 



> 2.0 



H 



W 



NEW MOON FIRST QTR FULL MOON LAST QTR 



LUNAR PHASE 



LU 

 Q 



CD 



O 



1.5 



1.0 



0.5 



< 



ty o.o 



-0.5 



NEW MOON FIRST QTR FULL MOON LAST QTR 



LUNAR PHASE 



Figure 4 



Mean density of postlarval penaeid shrimp (A) 

 Penaeus aztecus and (B) Penaeus setiferus 

 grouped by lunar phase during months of peak 

 abundance at Breach Inlet. Samples collected 

 near the bottom on flood tide during daylight 

 ( regular sampling). Log Density=log ( ( number/ 

 1,000 m 3 ) + 1). SD=standard deviation. Qtr= 

 quarter. Numbers in parenthesis=number of 

 samples. 



Peaks in abundance of P. setiferus postlarvae may be 

 related to prior spawning activity around new or full 

 moon phases, but this relationship is uncertain at 

 present and warrants further investigation. 



A relationship between recruitment of P. aztecus 

 postlarvae and subsequent commercial landings has 

 been difficult to demonstrate (Williams, 1969; Ford 

 and St. Amant, 1971; Baxter and Sullivan 4 ). Gener- 



Baxter. K. N„ and L. F. Sullivan. 1986. Forecasting offshore 

 brown shrimp catch from early life history stages. In Proc. 

 shrimp yield workshop. Tex. A&M Univ. Sea Grant Rep. TAMU- 

 SG-86-10:22-36. 



