FISHERY BUI. LFTIN VOI, 77, NO 



of distribution of individual species are described. 

 An attempt is also made to correlate these dis- 

 tributions with both biotic and abiotic parameters. 



STUDY AREA 



All sampling stations were situated within the 

 Cape Fear River, N. C, located at approximately 

 lat. 33° N (Figure 1 1. The estuary is relatively 

 narrow, averaging only 1.6-3.6 km wide and ex- 

 tending 45 km from the general location of the salt 

 boundary at Wilmington, N.C., to the river mouth 

 at Baldhead Island. A 12 m deep ship channel is 

 maintained from Wilmington to the river en- 

 trance, and numerous spoil islands are found adja- 

 cent to this channel over its entire length. Tidal 

 velocities in the Cape Fear are high, averaging 1 .5 

 m/s at the river mouth during ebb. 



Tidal salt marshes cover approximately 8,900 

 ha and form the largest contiguous system of this 

 type in North Carolina (U.S. Army Corps of En- 

 gineers-''). Dominant plant species include the 

 smooth cordgrass, Spartina alterniflora , and black 

 needle rush, J uncus roemerianus, with giant reed 

 grass, Spartina cyanosuroides, prevalent up- 

 stream at lower salinities. Tidal creeks cover an 

 estimated 648 ha, and shallow open water areas 

 (shoalsi between the channel and salt marshes 

 contribute an additional 7,285 ha of suitable nur- 

 sery habitat. 



MATERIALS AND METHODS 



Nine stations were established within several 

 major marsh systems and along the river shoals 

 (Figure 1; Table 1). Suitable interior marsh sites 

 could not be located in the middle reaches of the 

 estuary, since the few available creek systems 

 were inaccessible or could not be sampled without 

 great difficulty. Salinities at the chosen sites 

 ranged from to 35%o, and a wide variety of sub- 

 strata were included, ranging from soft organic 

 ooze, approximately 10-20 cm deep, to sandy areas 

 containing little organic material. Stations were 

 sampled on a monthly basis from January through 

 December 1977 with several exceptions (Table 1 ). 

 Because of ice cover, the Dutchman and Walden 

 Creek rotenone stations were not sampled in 

 January, and new stations were established at 



Shellbed Island and Hechtic Creek in February 

 and at Barnards Creek in April. 



Two collection methods were employed 

 throughout this study: seining, where footing was 

 satisfactory, and rotenone application i5'^f emul- 

 sifiable Fish-Tox-*), where softer mud or snags pre- 

 dominated. Before either method was attempted, 

 an area of tidal creek was isolated utilizing large 

 blocking seines. Nets were extended from shore to 

 shore and were anchored with U-shaped lengths of 

 concrete reinforcing rods, especially helpful in 

 pinning the leadline along the contours of the 

 banks on each side of the station (at several sites, 

 one shoreline was always bordered by a bar forma- 

 tion!. In addition, a length of heavy chain was 

 affixed to the leadline of each block net to ensure 

 direct contact with the substrate. Initially, 6.5 mm 

 mesh block nets were employed; beginning in 

 April 1977 these were replaced with fine mesh 

 (approxmiately 1.0 mm) nets capable of retaining 

 the smallest ocean-spawned larvae. The enclosed 

 area then was swept repeatedly with a 7.6 m, 6.5 

 mm mesh, seine or treated with sufficient rote- 

 none to kill all fish present. 



To determine the number of seine sweeps re- 

 quired, a study was conducted in October 1976 

 when nekton diversity remained near a yearly 

 maximum. After the block nets were set at the 

 Dutchman Creek site, a total of 13 sweeps were i 

 taken, and the contents of each sweep kept sepa- 

 rate. The results were plotted (Figure 2) as the 

 cumulative number of species, the expected 

 number of species (ENS) (Hurlburt 1971) and the ' 

 cumulative diversity (H', Shannon and Weaver 

 1949 ). As seen in the figure, little new information 

 was gained after the eighth sweep, i.e., an 

 asymptote was approached. A separate study at 

 Baldhead Creek in September 1977 confirmed 

 these results, and a procedure requiring eight 

 sweeps was instituted at each seine station.'^ In 

 addition, three overlapping sweeps with a 7.6 m, 

 approximately 1.0 mm mesh, seine were taken at 

 each site. These served to capture the smallest fish 

 present, those capable of passing through the 6.5 

 mm meshes. A preliminary experiment indicated 

 that these seines were capable of significantly re- 

 ducing the lower size range of key species studied 

 (Table 2). 



^U.S. Army Corps of Engineers. 1977. Maintenance of 

 Wilmington Harbor, North Carolina. Final environmental 

 statement. U.S. Army Engineers District, Wilmington. NC. 

 97 p. 



340 



^References to trade names does not imply endorsement by the 

 National Marine Fisheries Service. NOAA. 



^A50-ft 1 1.5-2 m) seine was used on the last sweep, this was the 

 original down.stream blocknet. 



