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Figure 6. — Abundance of Trinectes maculatus by station and season for 

 the North and South Santee Rivers. Ratios over bars indicate number of 

 collections where fishes were captured to total number of collections at a 

 station. 



tions in proximity to the river mouths, which suggests an 

 avoidance of euhaline areas by this fish. Lengths of hogchokers 

 ranged from 20 to 175 mm, but most individuals were < 80 mm. 

 These specimens probably represent young-of-the-year fish 

 (Dovel et al. 1969) which appear during all seasons due to the ex- 



tended spawning season of this species in the Carolinas 

 (Hildebrand and Cable 1938). 



Temporal and Spatial Distributions — Decapods 



Distributional patterns of the most abundant decapod crusta- 

 ceans, P. setiferus, P. aztecus, and Callinectes sapidus, are 

 shown in Figures 7 and 8. 



Penaeus setiferus, white shrimp. — Catches of white shrimp 

 were seasonal, with most individuals occurring in the Santee 

 system during the fall and summer. Though common in both 

 rivers, numerical abundance and biomass of white shrimp were 

 greater in the South Santee River (Table 2), and catches ap- 

 peared to be lower at the extreme upriver stations. This was par- 

 ticularly evident during winter and spring. Length-frequency 

 distributions showed young-of-the-year white shrimp were pres- 

 ent during summer in both rivers (Fig. 7). Sizes of shrimp col- 

 lected increased during the other seasons, with the largest in- 

 dividuals collected in the spring. Similar findings were noted by 

 Bishop and Shealy (1977) in a study of penaeid shrimp from 

 South Carolina estuaries. They found that the largest numbers 

 of shrimp were small, whereas larger individuals, which may be 

 derived from the overwintering population or from an im- 

 migrating offshore population, occurred during fall and spring. 



Penaeus aztecus, brown shrimp. — Brown shrimp were most 

 abundant in spring and summer (Fig. 8). These brown shrimp 

 were rare in winter trawl collections. In other South Carolina 

 estuaries, Bishop and Shealy (1977) noted that catches of brown 

 shrimp were strongly seasonal, with most individuals collected in 

 summer. The absence of brown shrimp in trawl catches during 

 the winter months does not indicate that they are absent entirely 

 from the estuary. Postlarval shrimp first enter South Carolina 

 estuaries in January and are most abundant in February and 

 March (Bearden 6 ). Because it appears that postlarval white 

 shrimp, and perhaps also brown shrimp, primarily occupy the 

 shallow edges and creeks of estuaries where cover and preferred 

 food are available (Bishop and Shealy 1977), we may have failed 

 to sample this component of the shrimp population by restric- 

 ting our collecting to the channel. It is also probable that 9-12 

 mm postlarvae are not retained by our 6 m otter trawl. Ex- 

 amination of length-frequency distributions (not shown) for 

 brown shrimp collected in the Santee system showed a total 

 absence of postlarvae in our trawl collections. Shrimp ranged 

 from 30 to 145 mm, with most individuals in the 55-90 mm size 

 range. The abundance of brown shrimp was also related to sta- 

 tion location and, hence, salinity as reflected in only one occur- 

 rence of P. aztecus at the extreme upriver sites. 



Callinectes sapidus, blue crab. — The blue crab was caught 

 throughout the North and South Santee Rivers during all 

 seasons. Catches did not reflect strong seasonal changes, 

 although fewer blue crabs were collected in summer in the North 

 Santee River. Catches also appeared to be related to sampling 

 location, with fewer blue crabs being caught at upriver stations. 

 Size-frequency distribution of blue crabs covered a wide range 

 of sizes from 1 5 to 1 95 mm, with smaller crabs ( < 60 mm) occur- 

 ring in fall. 



'Bearden, C. M. 

 in South Carolina. 



1961 . Notes on postlarvae of commercial shrimp {Penaeus) 

 Conirib. Bears Bluff Lab. No. 33, S p. 



11 



