A Five- Year Study of Seasonal Distribution and Abundance 



of Fishes and Decapod Crustaceans 



in the Cooper River and Charleston Harbor, S.C., 



Prior to Diversion 



E. L. WENNER, W. P. COON III, M. H. SHEALY, Jr., and P. A. SANDIFER 1 



ABSTRACT 



Fluctuations in the distribution and abundance of fishes and decapod crustaceans collected In a 6 in otter 

 trawl net from the Cooper River-Charleston Harbor estuarine system (South Carolina, USA) were examined over 

 a 5-year sampling period. A total of 101 fish species and 41 decapod crustacean species were collected. Species 

 richness was greatest at stations nearest the harbor mouth. Annual fluctuations in species abundance were 

 apparently related to low bottom-water temperatures which affected year-class strength. Ten species accounted 

 for -90% of the total number and -71% of the total biomass of fin fishes collected in the estuary: Stellifer 

 lanceolatus. Anchoa mitchUli, Micropogonias undulatus, Brevoortia tyrannus, Leiostomus xanthurus, 

 Symphurus ptagiusa, Bairdiella chrysoura, Cynoscion regalis, Urophycis regia, and Trinectes maculatus. The 

 decapod crustaceans Penaeus settferus, P. aztecus, Xiphopenaeus kroyeri, and Callinectes sapidus dominated 

 the fin fishes in abundance but not biomass. They composed -96% by number and -97% by weight of the 

 total decapod fauna. The biomass of fishes from this study is lower than values reported for other estuaries 

 along the Atlantic coast of the United States. 



The Cooper River-Charleston Harbor estuarine system, an important nursery area for fishes and decapod 

 crustaceans, is characterized by gradual changes in faunal assemblages and considerable overlap in spatial dis- 

 tributional patterns of resident and transient species. Numerically dominant species of fish and decapod crusta- 

 ceans form assemblages which are spatially and temporally ubiquitous. Resident estuarine species and stenohaline 

 marine species are more restricted in their distribution. 



INTRODUCTION 



Charleston Harbor and its tributary, the Cooper River, have 

 been subjected to greatly increased man-made alterations since 

 1942. Prior to that time, the Cooper River was a relatively 

 small coastal plains stream with a watershed of 1.86 million 

 km 2 . After construction of Pinopolis Dam across the upper 

 watershed of the Cooper River and creation of Lake Moultrie, 

 input of freshwater to the Cooper River increased, resulting in 

 inundation of marshes and abandoned rice fields. Increased 

 freshwater flow into Charleston Harbor decreased salinity 

 (Zetler 1953) and formed density currents with a predominant 

 upstream bottom flow throughout most of the lower 18 km of 

 the harbor. As a consequence, sediments were trapped within 

 the harbor and shoaling increased considerably (U.S. Army 

 Corps of Engineers 2 ). In turn, the shoaling has caused an 

 increase in dredging costs and depletion of available disposal 

 sites within the harbor. Because of this situation, the Army 

 Corps of Engineers will redivert water flow in 1983 from Lake 

 Moultrie into the Santee River system to effect a reduction of 

 flow into the Cooper River. 



Marine Resources Research Institute, South Carolina Wildlife & Marine 

 Resources Department, P.O. Box 12559. Charleston, SC 29412. 



! U.S. Army Corps of Engineers. 1975. Final Environmental Statement: 

 Cooper River Rediversion Project, Charleston Harbor, S.C.) U.S. Army Corps 

 of Engineers, Charleston District Office, Charleston, SC 29403. 201 p. 



The proposed rediversion probably will produce significant 

 changes in estuarine habitat as well as in populations of estu- 

 arine organisms, such as fishes and decapod crustaceans. To 

 assess possible effects of rediversion on population structure, 

 spawning success, and distribution of these organisms, it is 

 necessary to determine species composition, abundance, and 

 distribution prior to the perturbation. This paper describes 

 fluctuations in these parameters over a 5-yr period for fishes 

 and decapod crustaceans in the Cooper River-Charleston 

 Harbor estuarine system. 



STUDY AREA 



The Cooper River is classified as a mixohaline system, in 

 which the salt wedge extends along the bottom to Big Island 

 (Station C002) and bottom salinities decrease from about 

 27°/oo at Cummings Point (Station J003) to freshwater at the 

 Tee (Station C001) (Mathews and Shealy 1978) (Fig. 1). 

 Charleston Harbor is a stratified or salt-wedge estuary with 

 saltwater intrusion primarily a function of the tidal range and 

 the amount of freshwater released by the Santee-Cooper Dam. 

 A salinity differential between top and bottom strata of the 

 harbor causes the bottom flow currents to predominate over 

 the bottom ebb currents, with the result that upstream move- 

 ment of the bottom currents within the saline region of the 

 harbor forms a sediment trap (South Carolina Wildlife and 



