WEINSTEIN ET AL.: RETENTION OF THREE TAXA OF POSTLARVAL FISHES 



formulated which relates these behavioral re- 

 sponses to the maintenance of a preferred position 

 within the estuary. 



STUDY AREA 



The Cape Fear River estuary (approximately 

 lat. 33° N) is relatively narrow, averaging only 

 1.6-3.6 km in width and extending 45 km from the 

 general location of the salt boundary at Wil- 

 mington, N.C., to the river mouth at Baldhead- 

 Smith Island (Figure 1). A 12 m deep ship channel 

 with a width of 120-150 m is maintained from 

 Wilmington to the river entrance, and adjacent 

 spoil islands are found along its entire length. 

 Tidal velocities in the Cape Fear are high, averag- 

 ing 2.1 m/s during ebb near the city of Southport, 

 N.C. (National Ocean Survey 1977). Recent hy- 

 drographic and dye studies (Carpenter^) have es- 

 tablished that a two-layer system occurs in the 



estuary between the vicinity of Sunny Point and 

 Wilmington (Figure 1). 



Extensive tidal salt marshes cover about 8,900 

 ha and form the largest contiguous system of this 

 type in the State of North Carolina (U.S. Army 

 Corps of Engineers^). Tidal creeks cover an esti- 

 mated 648 ha, and shallow open water areas 

 (shoals) between the channel and salt marshes 

 contribute an additional 7,285 ha of suitable nur- 

 sery habitats for the young of fishes and shellfish. 



MATERIALS AND METHODS 



A modified version of the gear designed by 

 Graham (1972) was employed in this study (Fig- 

 ure 2A). Individual 0.5 m plankton nets with 

 stainless steel cod end buckets were suspended 

 from aluminum collars (Figure 2B) and bolted 

 onto orienting vanes attached to a 9.5 mm diam- 



••Carpenter, J. H. 1979. Dye tracer and current meter 

 studies. Cape Fear Estuary 1976", 1977 and 1978. Final report 

 to the Carolina Power & Light Co., Raleigh, N.C, 339 p. 



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

 Wilmington Harbor, North Carolina. Final environmental 

 statement. U.S. Army Engineers District, Wilmington, N.C, 

 97 p. 



LIGHT 



5m PLANKTON NET 



Figure 2. — A. Sampling apparatus and deployment, the middepth nets were not used on the east and west shoals. B. Detail of the 



orienting vane and net mounting. Paired meters were used on all bottom nets. 



421 



