FISHERY BULLETIN: VOL. 78, NO. 2 



bottom oriented during this period. In studies of 

 feeding by postlarval fishes in the Newport River 

 estuary, N.C., Peters and Kjelson ( 1975) and Kjel- 

 son et al. (1975) demonstrated that spot were ac- 

 tively feeding only during the daytime and de- 

 scribed them as carnivorous sight feeders. If the 

 nighttime surface orientation observed for floun- 

 ders and spot is not related to feeding activity, 

 then to what might it be attributed? 



We suggest that active migration into the 

 marshes is aided by surface movement on flood 

 tide at night. Since the mouths of many of these 

 tidal creeks have sills, and since most are shallow 

 and lack stratification, remaining near the bottom 

 in the main stem would not aid postlarvae in lat- 

 eral movements into the marshes. However, by 

 staying near the surface on night flood tides, large 

 numbers of individuals would be carried laterally 

 into the marshes and other shoal areas, perhaps 

 with the additional advantage of lower predation 

 pressure. 



Once in the marsh or other suitable shallow 

 area, a tidal response elicited on ebb, i.e., a ten- 

 dency to seek boundary layers near the bottom or 

 toward the banks, would allow at least some mem- 

 bers of the cohort carried into the system on flood 

 to remain on ebb (Lewis and Mann 1971). This 

 percentage need not be very high on each tidal 

 cycle to produce a rapid population accumulation. 



Species displaying a greater tendency to remain 

 in the lower layers over 24 h should not be present 

 in great numbers in shallow areas. This is pre- 

 cisely the case for Atlantic croaker. The marshes 

 in the Cape Fear are not a major nursery zone for 

 this species, as demonstrated by the nearly com- 

 plete absence of postlarval Atlantic croaker from 

 this habitat (Weinstein 1979). A noteworthy 

 paradox arises when this species is considered 

 over most of its geographic range. Atlantic croaker 

 seem to prefer those estuaries with deep channels 

 and are not taken in large numbers in the shallows 

 (Welsh and Breder 1923; Wallace 1941; Suttkus 

 1955; Haven 1957; Nelson 1969; Chao and Musick 

 1977). It is suspected that in these estuaries, post- 

 larval Atlantic croaker maintain their general 

 bottom orientation and do not move laterally to 

 any great extent; however, in several shallow es- 

 tuaries along the Gulf of Mexico (Herke 1971; 

 Parker 1971; Arnoldi et al. 1974; Yakupzack et al. 

 1977) young Atlantic croaker make extensive use 

 of the marsh shallows. Thus, in those situations 

 where deep channels are not predominant fea- 

 tures of the system, Atlantic croaker will make 



use of the marsh shallows. This difference in dis- 

 tribution in the Gulf States might be further rec- 

 onciled if temperature is taken into consideration. 

 Temperature as a potential limiting factor for At- 

 lantic croaker year class success in most middle 

 Atlantic coast estuaries has been discussed by 

 Joseph (1972). Remaining in the warmer waters of 

 the deep channel during winter might enhance 

 Atlantic croaker survival. The winters of 1976-77 

 and 1977-78 along the Atlantic coast have been 

 colder than usual; greater utilization of shallow 

 areas by Atlantic croaker might occur in warmer 

 years. 



Others also have observed that the river main 

 stem at the head of the Cape Fear estuary is a 

 primary nursery zone for Atlantic croaker and, to 

 a more limited extent, for spot and flounders 

 (Copeland et al. see footnote 8). In addition, the 

 boundaries of this zone for certain species are dic- 

 tated by freshwater flows and tend to shift with 

 these flows. Although not captured quantita- 

 tively, larger spot and Atlantic croaker accumu- 

 lated upriver in the vicinity of buoy 50 (Figures 6, 

 7). Although flounders were not measured, a simi- 

 lar result would be expected for these species. 



In summary, we believe the data presented are 

 consistent with the hypothesis that postlarvae 

 exhibit behavioral patterns with respect to photo- 

 period and tide which are instrumental in en- 

 abling these organisms to: 1) accumulate in up- 

 stream nurseries by utilizing net nontidal flows in 

 the lower layer, 2) make strong lateral movements 

 into the marsh nurseries by migrating to the sur- 

 face on flood tide at night, and 3) stay in both of 

 these primary nurseries by dropping lower into or 

 effectively out of the water column on ebb. The 

 tidal response may be particularly important in 

 well-mixed estuaries where upstream drift in the 

 lower layers is negligible. In fact, it might be the 

 primary mechanism employed by postlarvae to 

 penetrate estuaries and reach suitable nursery 

 habitats. 



ACKNOWLEDGMENTS 



We are grateful to the biotechnicians of Lawler, 

 Matusky & Skelly Engineers (LMS) for their con- 

 scientious efforts in the field and laboratory and to 

 W. Werth for his assistance in constructing the 

 sampling gear. We also would like to thank K. L. 

 Heck, Jr., D. T. Logan, J. P. Lawler, and R. L. 

 Wyman for their many useful suggestions for im- 

 proving the manuscript. Appreciation is extended 



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