20% of the catch was measured; when >500 were caught, 10% 

 of the catch was measured. 



Data Analysis 



Cluster analysis was used to define assemblages of fishes and 

 decapod crustaceans and to determine degree of similarity 

 among stations. Prior to cluster analysis, data were loga- 

 rithmically transformed by log, (x + 1), where x is number of 

 individuals for a given species. We reduced data by elimination 

 of species which occurred in fewer than three collections during 

 a sampling period and by elimination of collections which con- 

 tained only one species. 



The methods of cluster analysis used are described in detail by 

 Boesch (1977). The Bray-Curtis coefficient (Clifford and 

 Stephenson 1975) was used to compute similarity values. Sym- 

 metrical similarity matrices were computed for both the North 

 and South Santee Rivers on data from the 2-yr sampling period 

 with collections as entities and species as attributes (normal 

 analysis), and with species as entities and sites as attributes (in- 

 verse analysis). Entities were classified into related groups by 

 using flexible sorting (Lance and Williams 1967) with /3 = 

 -0.25. 



Two separate dendrograms were generated for each river: A 

 dendrogram which indicated association of all collections during 

 the 2-yr sampling period based on their faunal content and a 

 dendrogram which indicated association of all species from the 

 collections made during the 2-yr sampling period. We used 

 postclustering techniques of nodal analysis (Williams and 

 Lambert 1961; Lambert and Williams 1962) to examine species 

 and station coincidences. Nodal analysis diagrams were made by 

 using patterns of constancy (a measure of how consistently a 

 species is found in a site group) and fidelity (a measure of how 

 restricted a species is to a site group). 



An index of abundance (Musick and McEachran 1972; Elliott 

 1977) was used to compare numbers and weights of selected 

 dominant species and is expressed as: 



Index of Abundance = — Yl log l0 (x + 1), 

 I 



where x = number or weight of individuals of a given species 

 and n = number of collections in a chosen time frame. 



We determined biomass and density estimates for fishes and 

 decapods from computations of area swept for trawl gears. 

 Estimates of area swept (a) were determined by the following 

 equation given by Roe (1969): 



K x M x (0.6 H) 

 10,000 mVha 



where K is speed in meters per hour, Mis time in hours fished, 

 and H is headrope length in meters (Klima 5 ). Roe (1969) as- 

 sumed an effective swath of about 60% of the headrope length 

 as established by Wathne (1959). The area swept by our 6 m 

 otter trawl was estimated to be 0.72 ha/tow based on the 

 method described by Roe (1969). 



'Kiima, E. F. 1976. A review of Ihe fishery resources in the western central 

 Atlantic. West. Cent. Atl. Fish. Comm. Publ. 3, 77 p. 



RESULTS 



Hydrographic Parameters 



Bottomwater temperatures were very similar between rivers 

 and among stations. Temperatures were lowest in both the 

 North and South Santee Rivers during February and March 



1975 and January and February 1976. In the North Santee 

 River, temperatures gradually increased from April to reach a 

 peak in either August (1976) or September (1975). The warmest 

 month in the South Santee River during both years of sampling 

 was August. Based on temperature over the 2-yr sampling 

 period, winter encompassed January, February, and March; 

 spring, April, May, and June; summer, July, August, and 

 September; and fall, October, November, and December. 



Salinities were extremely variable both seasonally and among 

 stations. Freshwater outflow increased in the Santee watershed 

 from 14.2 mVs to an average of 679.3 m 3 /s between mid-March 

 and mid-April 1975 and to 238.5 mVs from mid-May until late 

 June 1975 (Burrell 1977). These freshets considerably lowered 

 salinities at stations in both rivers. Salinities were also variable in 



1976 but the extreme fluctuations caused by freshwater outflow- 

 were not as evident as in 1975. Except during periods of high 

 runoff when freshwater was found throughout the system, 

 salinity decreased from stations located at the river mouth to 

 those located upstream. Salinities at stations SS01 and NS01 

 ranged from 0.2 to 32.9 % , which characterized these stations 

 as limnetic-euhaline by the Venice System (Symposium on the 

 Classification of Brackish Waters 1958). Stations SS04 and 

 NS04 were limnetic-polyhaline (0.1-26% o ), while SS07 and 

 NS07 were limnetic-mesohaline (0.1-15.9% o ). Salinities at NS11 

 and SS11 ranged from <0.1 to \A°/ oa and were within the 

 limnetic-oligohaline salinity regime. 



Community Composition and Diversity 



Eighty species of fishes were collected from the South Santee 

 River and 64 species from the North Santee River during the 

 1975-76 sampling period (Table 1). Eleven species accounted for 

 93% of the total number of specimens and 70% of the total fish 

 biomass taken in both rivers: Atlantic croaker, Micropogonias 

 undulatus; bay anchovy, Anchoa mitchilli; silver perch, Bair- 

 diella chrysoura; star drum, Stellifer lanceolatus; white catfish, 

 Ictalurus catus; weakfish, Cynoscion regalis; threadfin shad, 

 Dorosoma petenense; spot, Leiostomus xanthurus; hogchocker, 

 Trinectes maculatus; Atlantic menhaden, Brevoortia tyrannus; 

 and blackcheek tonguefish, Symphurus plagiusa. In both rivers, 

 M. undulatus was the most abundant species collected. With 

 regard to biomass, however, M. undulatus was outranked by /. 

 catus in the North Santee River and Bairdiella chrysoura in the 

 South Santee River. 



The decapod crustaceans were represented by 22 species in the 

 North Santee River and 18 species in the South Santee River. 

 Although fewer species of decapods than fish were collected, the 

 decapods dominated in terms of total number of individuals 

 captured (Table 2). The numerical dominance of the decapods 

 was due to extremely large catches of the white shrimp, Penaeus 

 setiferus, especially in the South Santee River. This species was 

 by far the most abundant decapod collected in both rivers and 

 also dominated other decapods in terms of biomass. Penaeus 

 setiferus, together with the brown shrimp, P. aztecus, and the 

 blue crab, Callinectes sapidus, comprised over 96% by number 

 and weight of the total decapod fauna collected in both rivers. 



