FISHERY BULLETIN. VOL. 78, NO. 2 



eter nylon rope. Tidal flows in the Cape Fear es- 

 tuary were sufficiently high to fully extend these 

 nets during the sampling period. Lead weights (66 

 kg) between the anchor and bottom net were used 

 to fix the depth at which the bottom nets fished, 

 and a tag line and float attached to the anchor 

 shaft allowed each rig to be easily retrieved at the 

 end of the sampling period. Surface nets were 

 rigged to sample at 1.5 m below the surface, mid- 

 depth nets at a depth of 6.5 m (in the main chan- 

 nel), and bottom nets, approximately 1 m above 

 the substrate. In order to reduce detection by post- 

 larvae, all nets were dyed deep brown (Rit^ #20, 

 Cocoa Brown — W. Watson''). 



Samples were collected at two locations on three 

 sets of dates: 14-15 March, 5-6 April, and 11-12 

 April. A pair of closely spaced transects were 

 situated near river buoy 50, close to the head of the 

 estuary, and another pair at river buoy 32, at 

 Snow's Cut (Figure 1). Two vessels were employed 

 on each sampling date, and for each transect, three 

 stations were established across the main channel 

 from east to west. At slack water the east and west 

 shoal rigs were set first in 7.6 m of water, and the 

 channel station nets were anchored last. All nets 

 at each of the paired transects were set in <40 

 min. Because the period of slack water continued 

 for the duration of the setting process, the nets 

 actually began to fish simultaneously and, except 

 for the period of retrieval (about 20 min), a nearly 

 synoptic set of samples was taken across a cross 

 section of the main channel and shoals. On each 

 pair of dates four consecutive tides were sampled, 

 with nets retrieved after 2 h. Limiting the sam- 

 pling period to 2 h was a necessary precaution in 

 this study because of the potential for net clogging 

 in the highly turbid Cape Fear estuary (see below). 



It was planned to sample two nighttime and two 

 daytime tides during each survey but, due to dif- 

 ferences in the predicted and actual tides, there 

 was sufficient ambient light to read field data 

 sheets by the end of the last night set at buoy 50 on 

 6 April. For this reason, the sample was excluded 

 from the analyses. 



To reduce the potential for clogging, nets were 

 constructed of 752 /xm mesh material and tapered 

 to a length of 3 m. Meshes of this size allowed the 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



'W. Watson, Associate, Cape Fear Estuarine Laboratory, 

 North Carolina State University, Southport, N.C., pers. com- 

 mun. September 1976. 



422 



passage of many small plankton as well as fine 

 detritus, but retained the postlarvae [—7-34 mm 

 SL (standard length)! of interest. Previous studies 

 of comparative length frequency in 505 and 760 

 /xm nets (Copeland et al.^) indicated that postlar- 

 vae <7 mm (of the species of interest) were un- 

 common in the Cape Fear estuary, since they were 

 recruited from well offshore. 



In a preliminary experiment in November 1976, 

 five nets were fished near the bottom, off a tidal 

 creek bridge, and pulled sequentially every 0.5 h 

 after an initial fishing period of approximately 1.0 

 h (Table 1). The flow past each net was monitored 

 by a TSK^ meter mounted in the center of the 

 mouth of each net and by a second meter affixed to 

 the collar support. After more than 3 continuous 

 hours of fishing at relatively low flows (compared 

 with the main channel), clogging, as determined 

 by the difference between the inside and outside 

 meter readings, did not exceed 28% on the last net 

 pulled. However, a piece of filamentous algae was 

 found wrapped around the inner TSK prop and 

 axle on this net, restricting free movement. Meter 

 fouling caused by fibrous detritus and algae along 

 the river bottom created considerable difficulties 

 in obtaining useful bottom meter readings in the 

 actual experiments and was deemed a more seri- 

 ous problem than severe net clogging. 



In an attempt to overcome bias due to fouled 

 meters, all bottom nets were fitted with paired 

 TSK meters as described above. Based upon the 

 results of the preliminary study (Table 1), it was 

 conservatively estimated that an inside meter 



^Copeland, B. J., R. G. Hodson, and R. J. Monroe. 

 1979. Larvae and postlarvae in the Cape Fear River estuary. 

 North Carolina, during operation of the Brunswick Steam Elec- 

 tric Plant, 1974-78. Report 79-3 to Carolina Power & Light Co., 

 Raleigh, N.C., 214 p. 



^Tsurumi Seiki Kosakusho Company. 



Table l. — Preliminary net clogging study at Walden Creek, 

 Cape Fear River. Negative percentage difference indicates that 

 inside meter reading was largest. 



'A piece of filamentous algae was found wrapped around tfie TSK prop and 

 axle, restricting free movement. 



