FISHERY BULLETIN: VOL. 78, NO. 2 



Table 2. — Comparison of mean density (number/1,000 m^) at buoy 32 versus buoy 

 50 for spot, Atlantic croaker, and Pamlichthys spp. 



"Significant at a = 0.05; transformed log(10 + X) data utilizing error mean squares from initial 

 ANOVAs. 



'Last nigfit set omitted. 



March at buoy 50 and 5-6 April at buoy 32, catches 

 at night exceeded those taken during daylight 

 (Table 3). A similar pattern did not emerge for spot 

 and Atlantic croaker, although night values on 

 11-12 April at both buoys were significantly 

 higher. Apparently, net avoidance was negligible 

 in this study, unlike the findings of Graham 

 (1972), who limited his sampling for larval Atlan- 

 tic herring to night hours in the Sheepscot estuary 

 because of what he described as excessive daytime 

 net avoidance. High tidal velocities and the turbid 

 waters of the Cape Fear estuary may have been 

 partially responsible for this difference. Flounders 

 were either better able to detect the dyed nets or 

 perhaps exhibited somewhat different diurnal be- 

 havior; e.g., a greater tendency to rest on the bot- 

 tom during the day. 



A response to light was further established by 

 an examination of the photoperiod by depth in- 

 teractions for the three taxa. During the day, spot 

 and Atlantic croaker were most abundant at the 

 bottom and at middepth. Only in the partial data 

 sets analyzed on 5 April 1978 and for Atlantic 

 croaker at buoy 32 on this date was this pattern 

 changed. On this date, depth distributions did not 

 differ for Atlantic croaker and the surface con- 

 centration for spot at buoy 50 was not significantly 

 smaller than the channel middepth value. The 

 trend for flounders was similar, although not as 

 distinct as for the other species. At night, all three 

 taxa moved higher in the water column but to 

 differing degrees. Whereas flounders and spot 

 tended to congregate nearer to the surface, most 

 Atlantic croaker remained lower in the water col- 

 umn (Table 3). 



Of the five significant photoperiod by depth in 

 teractions involving flounders, a posteriori tests 

 conducted for night data indicated that surface 

 concentrations in four instances were sig- 



426 



nificantly greater than at all other depths. Spot 

 also tended to accumulate toward the surface, on 

 the two dates at buoy 32 where a significant in- 

 teraction was detected, night catches at the sur- 

 face exceeded those at the bottom; in the main 

 channel, however, surface and middepth concen- 

 trations were not significantly different, although 

 the mean for the former always exceeded that of 

 bottom values by a substantial margin. 



The best indication of a diel movement by At- 

 lantic croaker occurred in the main channel where 

 the mean for surface night collections diverged 

 less from that of other depths (see also Figure 4), 

 while during the day, the mean for surface collec- 

 tions was usually significantly lower. No surface 

 accumulation was detected for Atlantic croakers 

 on the shoals, on the single date where a sig- 

 nificant difference was observed, bottom catches 

 were greater than at the surface. 



Response to Tide 



Ebb tide catches were generally lower for all 

 taxa than those of corresponding flood tides (Fig- 

 ures 3-5). In addition, a shift in catch density from 

 channel middepth toward the bottom occurred on 

 ebb, and in several instances bottom concentra- 

 tions exceeded those of middepth nets for all 

 species. 



The observed difference between ebb and flood 

 concentrations was always significant for floun- 

 ders, and on two occasions, for Atlantic croaker. 

 Tide alone did not seem to exert a major influence 

 on the concentrations of spot, although a sig- 

 nificant tidal effect was observed on 14-15 March 

 1978. 



All three taxa displayed a trend towards larger 

 flood catches on the eastern shoal and in the chan- 

 nel, while on ebb the western shoal often exhibited 



