Although Wallace and Van der Elst (1975) and Livingston et 

 al. (1976) also found that juveniles predominated in their 

 samples, we suspect that sampling design and gear selectivity 

 may have biased our results toward juvenile fishes. Our choice 

 of fixed stations is certainly biased and lends itself to sampling 

 error that would have been eliminated or reduced by a stratified 

 random design (Markle 1976). We are, therefore, not able to 

 determine the influence of movements by the fauna between the 

 shoals and the channel. Because trawling is inherently variable 

 (Taylor 1953), a repetitive method of collection would have 

 allowed for statistical analysis of sampling efficiency to deter- 

 mine whether hauls taken at different times in different places 

 did indeed have significantly different catches (Barnes and 

 Bagenal 1951; Livingston 1976). However, even with successive 

 samples, it is difficult to determine whether variability arises 

 from the spatial distribution of the organisms or from the gear 

 utilized (Taylor 1953). The susceptibility of organisms to fishing 

 gear undoubtedly has influenced perception of spatial and tem- 

 poral patterns (Markle 1976). The relatively small, fine-mesh 

 bottom trawl used in our study is selective toward capture of 

 slower, smaller fish. The relative absence of great numbers of 

 older, larger fish from our trawl catches cannot be attributed en- 

 tirely to migration or habitat selection, but in all likelihood 

 reflects at least partial avoidance or escapement from the 6 m 

 trawl (Shealy et al. 1974). 



Habitat differences between adult and juvenile fishes may 

 also account for the lack of large fish in our samples. Habitat 

 preference varies with the species and also with age (Wallace and 

 Van der Elst 1975; White and Chittenden 1976), so that feeding 

 and residential grounds of adult fishes often are separate from 

 their spawning grounds and nurseries. If spatial separation exists 

 in South Carolina waters, then our survey was biased toward 

 collection of juveniles found primarily in the channel. However, 

 tidal creeks of the Cooper River which are comparable in sa- 

 linity to those near the intermediate and upriver stations oc- 

 cupied in the Santee system were dominated by young-of-the- 

 year marine euryhaline species such as M. undulatus, A. 

 mitchilli, L. xanthurus, B. chrysoura, and Paralichthys 

 lethostigma (Turner and Johnson 1974). Although the impor- 

 tance of tidal creeks in the Santee system as nursery areas can 

 only be inferred, it is likely that the limitation of our survey to 

 the channel resulted in minimal estimates of juvenile abundance 

 for the river system. 



The lower estimated biomass of fishes in the Santee system 

 and other South Carolina estuaries is a direct function of the 

 predominance of juvenile fishes in our catches and the effi- 

 ciency of the sampling gear used. Whereas the density of fish 

 from this area compares favorably with other regions, the 

 biomass is much less. The large biomass of fishes in New 

 England estuaries is primarily due to large catches of winter 

 flounder, Pseudopleuronectes americanus (Oviatt and Nixon 

 1973; Haedrich and Haedrich 1974). A comparison of biomass 

 and density estimates from this study and others (see Table 5) 

 which used small trawls towed in the channel with investigations 

 which incorporated shallow tidal creek and marsh sampling 

 (e.g., Turner and Johnson 1974) indicates that the most produc- 

 tive areas are the marsh-creek habitat. Because these areas of the 

 system were not sampled and the efficiency of our gear was low, 



'Van Engel, W. A., and E. B. Joseph. 1968. Characterization of coastal and 

 estuarine fish nursery grounds as natural communities. U.S. Fish Wildi. Serv. 

 Final Rep., 43 p. 



our biomass and density estimates should also be considered 

 minimal. 



The presence of juvenile fishes in the Santee system is 

 especially important in considerations concerning the effects of 

 rediversion. Juvenile stages of resident species and many 

 estuarine transient species are tolerant of and may even be most 

 abundant in lower salinity water (Gunter 1961). Therefore, we 

 believe that the nursery habitat for resident estuarine fishes will 

 not be detrimentally affected and may be increased by re- 

 diversion. 



Because rediverted flow of water through the Santee system 

 will be moderate compared with the tremendous discharge of 

 freshwater (9,100 mVs) put into the Chesapeake Bay estuarine 

 system by Hurricane Agnes (Chesapeake Bay Research 

 Council 1973), we do not anticipate that juvenile fishes will be 

 passively swept from the Santee Rivers into the coastal area. In 

 contrast, the food supply of fishes may be altered in that sup- 

 plies of benthic organisms could increase in oligohaline and 

 brackish water areas but decrease in lower reaches of the river. 

 This effect could be particularly detrimental if it occurred 

 during summer. Andrews (1973) noted that floods during warm 

 seasons cause silting and an influx of excessive nutrients and 

 organic matter, with consequent algal blooms and stratification 

 of waters. These factors may, in turn, lead to low dissolved 

 oxygen conditions. During other seasons, increased accumula- 

 tions of detritus caused by increased riverflow and salinity 

 alterations could actually be beneficial to microorganisms and 

 detritivores such as isopods, amphipods, and some decapods. 

 Detritus also serves as the major energy base utilized by 

 juveniles of most fish species from sea grass beds (Carr and 

 Adams 1973) and is probably important as a direct or indirect 

 source of food for many fishes in the Santee system. 



Sustained abundance of Penaeus setiferus in the Santee 

 system is questionable following rediversion. Shrimp are known 

 detritivores, and large areas of brackish/salt marsh and estuary 

 with substantial land runoff are considered to be conducive to 

 good shrimp production (Bishop and Shealy 1977). Rediversion 

 will cause waters to inundate many areas and should result in a 

 seaward progression of freshwater and brackish water plant 

 communities. Because the total area of estuarine habitat should 

 effectively be moved seaward, a decrease in actual acreage 

 available as nursery habitat may result; yet lower salinity condi- 

 tions are still likely to exert the greatest influence on shrimp pro- 

 duction. Young P. setiferus are most abundant in salinities 

 <10%o, whereas young P. aztecus are most abundant in 

 salinities from 10 to 20 % (Gunter et al. 1964). Despite these op- 

 timum ranges, Barrett and Gillespie (1973, 1975) have suggested 

 that an inverse relationship exists between the amount of 

 freshwater introduced into coastal Louisiana and the catches of 

 brown and white shrimp. Also, increased turbidity and hyper- 

 trophy may inhibit photosynthesis so that an initial reduction in 

 oxygen may occur in bottom waters. Others (Hildebrand and 

 Gunter 1953; Copeland 1966; Aleem 1972; Glaister 1978) have 

 noted a positive relationship between shrimp abundance and 

 river discharge, but not all of these studies indicated that abun- 

 dance was increased within the estuary. 



Blue crabs will probably be little affected by rediversion be- 

 cause of their high mobility and tolerance of low-salinity condi- 

 tions, but increased siltation from rediversion could hamper 

 their respiration. Although blue crab populations sustained little 

 damage following Hurricane Agnes, mortalities in Chesapeake 

 Bay were attributed to increases siltation, low dissolved oxygen 

 levels, and red tide (Chesapeake Bay Research Council 1973). 



15 



