A Profile of the Fish and Decapod Crustacean 



Community in a South Carolina Estuarine System 



Prior to Flow Alteration 1 



ELIZABETH LEWIS WENNER, MALCOLM H. SHEALY, JR., and PAUL A. SANDIFER 2 



ABSTRACT 



The seasonal distribution and abundance of fishes and decapod Crustacea collected by 6 m otter trawl from the 

 North and South Santee Rivers, South Carolina, were examined over a 2-year sampling period. Species richness was 

 greatest during summer and at stations located in proximity to the river mouths. Although species richness was found 

 to be related to salinity, temperature, depth, and dissolved oxygen, it was most noticeably affected by a spring freshet 

 which considerably lowered richness and abundance. 



Eleven species accounted for 93°Io of the number and -10% of the total fish biomass taken in both rivers: 

 Micropogonias undulatus, Anchoa mttchilli, Bairdiella chrysoura, SteWfer lanceolatus, Ictalurus catus, Cynoscion 

 regalis, Dorosoma petenense. Leiostomus xanthurus, Trinectes maculatus, Brevoortia tyrannus, and Symphurus 

 plagiusa. White shrimp, Penaeus setiferus; brown shrimp, P. aztecus; and blue crabs, Callinectes sapidus, comprised 

 over 96% by number and weight of the decapod fauna collected in both rivers. Dominant fishes were present in fairly 

 equal abundance throughout the year and utilized the Santee system as either a residential or nursery area, while P. 

 setiferus and P. aztecus were more seasonal in their pattern of appearance and abundance. 



Length-frequency analysis showed the Santee system fish fauna to be composed mostly of juvenile specimens. 

 Their presence throughout the year indicated that the Santee is a temporally stable and relatively nonstressed system 

 and an important nursery area. 



The predominance of juveniles accounted for lower biomass (kg/ha) of fishes in the Santee system compared to 

 values for other estuaries along the Atlantic coast of the United States. The continued importance of juvenile fishes 

 and shrimp in the Santee system is questionable in view of salinity changes in the nursery habitat following proposed 

 river rediversion. 



INTRODUCTION 



A number of published accounts are available on community 

 ecology of estuarine fauna along the northeastern and south- 

 eastern coasts of the United States. Despite this, few com- 

 prehensive studies exist on distributional patterns and faunal 

 composition of estuarine megafauna, such as fishes and 

 decapods, from a system which has experienced as many 

 manipulations as the Santee River, S.C. The drainage basin of 

 the Santee encompasses 41,000 km 2 in North and South 

 Carolina. The Santee was the fourth largest river on the U.S. 

 east coast prior to diversion of most of its flow into the Cooper 

 River in 1942. Diversion not only lowered the annual mean 

 discharge from 525 m'/s to 74 m 3 /s but also caused severe shoal- 

 ing in Charleston Harbor at the mouth of the Cooper River 

 (Kjerfve and Greer 1978). Changes in the amount of freshwater 

 flow completely altered the supply and deposition of sediments, 

 erosion patterns, salinity regime, flooding characteristics, and 

 floral and faunal communities (Kjerfve 1976). After diversion, 

 the salinity in the Santee distributaries, the North and South 

 Santee Rivers, increased sharply. In addition, large quantities of 

 fine-grained suspended sediments were transported into the 

 Cooper River and, eventually, into Charleston Harbor. 



The costly necessity to dredge Charleston Harbor continuously 

 prompted a rediversion project begun in 1975 whereby 80% of 

 the Cooper River flow eventually will be directed back into the 

 Santee system (Kjerfve 1976). Upon projected completion of 



rediversion on the North and South Santee Rivers is purely 

 428 m'/s (Kjerfve and Greer 1978). Although the impact of 

 rediversion on the North and South Santee Rivers is purely 

 speculative, it is likely to reduce the net salinity in the Santee 

 system and increase amounts of fine-grained suspended 

 sediments. Kjerfve and Greer (1978) cautioned that these com- 

 bined changes may ultimately end the economically important 

 American oyster, Crassostrea virginica, and hard clam, 

 Mercenaria mercenaria, fisheries flourishing at present in this 

 river. The effect of rediversion on fishes and decapod Crustacea 

 also may be substantial. Shealy and Bishop (1979) suggested that 

 population changes in penaeid shrimp may occur, and the extent 

 of nursery areas may be affected. Fishes such as Ictalurus catus, 

 I. punctatus, Morone saxatilis, and Anguilla rostrata, which are 

 frequently encountered in lower salinity regions of estuaries, 

 may increase in abundance in the Santee system; however, the 

 effect on most species, such as the euryhaline sciaenid fishes 

 which are numerically dominant in South Carolina estuaries 

 (Shealy et al. 1974), cannot be predicted. 



The present study examines quantitative annual and seasonal 

 variability, diversity, and species assemblages of fishes and 

 decapod Crustacea found in the channel of the lower North and 

 South Santee Rivers. Our primary consideration is to describe 

 the megafaunal community as it currently exists and to relate 

 distributional patterns to abiotic factors which may influence 

 the community after rediversion. 



STUDY AREA 



Contribution No. 139 from the South Carolina Marine Resources Center. 

 •Marine Resources Research Institute, P.O. Box 12559, Charleston. SC 29412. 



All sampling stations were located within the Santee River 

 system (Fig. 1). The Santee River provides the major headwaters 



