FISHERY BULLETIN: VOL. 78. NO. 2 



10 



fO 



O 



< 



Ixl 



DD 



5 01 



^.001 



• • BUOY 32, n= 3659 



p— -o BUOY 50, n= 2 

 14-15 MAR 78 



J 



10 14 18 22 26 30 34 

 LENGTH (mm) 



6 10 14 18 22 26 30 34 



LENGTH (mm) 



CD <D 



1 1 -12 APR 78 



BUOY 32, n= 2017 

 BUOY 50, n= 4052 



Y\, « 





10 14 18 22 26 30 34 



LENGTH (mm) 



Figure 7. — Length-frequency distribution for Atlantic croaker, Micropogonias undulatus, on the three collecting dates. Only two 



individuals were captured in the vicinity of buoy 50 on 14-15 March. 



Most interestingly, during the high-flow period on 

 14-15 March 1978, when spot and Atlantic croaker 

 moved downriver, the larger fish accompanied the 

 newer recruits to the vicinity of buoy 32. This is 

 most evident in Figure 7 for Atlantic croaker. 

 With the return of the salt front above buoy 50 in 

 April, spot and Atlantic croaker returned up- 

 stream. For both species in this month, length- 

 frequency distributions at buoys 32 and 50 were 

 compared by Pearson chi-square tests. Significant 

 differences (P<0.05) were found for all compari- 

 sons, with larger fish predominating upstream. 



DISCUSSION 



In contemplating the retention of bivalve larvae 

 within the James River estuary. Wood and Hargis 

 (1971) stated, "The point at issue is not whether 

 such retention occurs, but whether evolved pat- 

 terns of larval behaviour contribute significantly 

 to the process." Evidence from the present investi- 

 gation supports the premise that, by displaying 

 specific behavioral responses, postlarvae of the 

 three taxa studied were able to reach and stay 

 within specific portions of the Cape Fear River 

 estuary. This occurred despite intensive tidal 

 flows and relatively high exchange ratios in the 

 system. 



Peak recruitment for winter-spawned larvae in 

 the Cape Fear estuary and many other Atlantic 



430 



coast estuaries occurs at a time when stratification 

 and tidal exchange ratios are usually at a yearly 

 maximum. The exchange ratio may exceed 0.70 in 

 the Cape Fear estuary and flows above 1,700 m^/s 

 have been recorded in January and February 1978 

 (Carpenter see footnote 4). Species recruited from 

 the ocean also have the peculiar problem of initial 

 entrance into the estuary and the avoidance of 

 being washed out on the subsequent tide. By re- 

 sponding to a combination of hydrographic fea- 

 tures of the estuary and perhaps to exogenous 

 variables these species are able to avoid net sea- 

 ward transport. 



Active responses to light and diel migrations in 

 the water column have been attributed to the lar- 

 vae of barnacles (Fales 1928; Bassindale 1936; 

 Bousfield 1955), oysters and other bivalves (Car- 

 riker 1951; Korringa 1952; Williams and Porter 

 1971: Wood and Hargis 1971), copepods (Schallek 

 1943), shrimp (Hughes 1969a, b, 1972; Williams 

 and Deubler 1968), and fishes (Rogers 1940; 

 Creutzberg 1961; Pacheco and Grant 1968; Lewis 

 and Wilkens 1971; Graham 1972; Smith et al. 

 1978). However, differential avoidance of nets 

 with respect to depth has also sometimes been 

 suggested as the cause of diel "migrations" (e.g.. 

 Fore and Baxter 1972). Results of comparative 

 studies using several kinds of collecting gear, in- 

 cluding high-speed trawls (Thayer et al. in press), 

 and the observed absence or low abundance of 



