732 



Fishery Bulletin 103(4) 



Inshore- 1986 



K 



mm 



£ 15l 



q- r 



Bt Sp Bs Pt Xn Ps Lx Mu Et Es 



Inshore- 1989 



Offshore- 1986 



Bt Sp Bs Pt Xn Ps Lx Mu Et Es 

 Offshore- 1989 



iEffl EE 



B- i- 



Bt Sp Bs Pt Xn Ps Lx Mu Et Es 

 Inshore- 1991 



Bt Sp Bs Pt Xn Ps Lx Mu Et Es 

 Offshore- 1991 





u 



Bt Sp Bs Pt Xn Ps Lx Mu Et Es 



Bt Sp Bs Pt Xn Ps Lx Mu Et Es 



Mean proportion of larval concentration at depth 



Figure 2 



Mean proportions of larvae sampled at depths at six stations on the southeast United States 

 shelf. Error bars indicate standard deviation of mean proportions calculated by using all the 

 samples collected at a station. The x-axis of all panels is the same and ranges from to 1.2. 

 The species indicated in each figure is denoted by a two letter code (P>t=Brevoortia tyrannus, 

 Sp = Syacium papillosum, B>s=Bothus spp., Pt=Peprilus triacanthus, Xn=Xyrichtys novacula, 

 Ps=Paralichthys spp., Lx =Leiostomus xanthurus, Mu=Micropogonias undulatus, Et=Etrumeus 

 teres, and Es=Etropus spp.). Species are grouped by an a priori assignment of their general 

 outcome of transport. 



the ingress of other species occurs during northwest, 

 west, and southwest winds; 2) ingress of B. tyrannus 

 is not related to wind, and ingress of the other species 

 is related to northwest, west, and southwest winds; 3) 

 and ingress of all estuarine-dependent species occurs 

 during similar wind forcing. Other studies have estab- 

 lished similar a priori predictions for relations between 

 wind forcing and ingress, yet results have been equivo- 

 cal (e.g., Blanton et al., 1995). One explanation is that 

 cross-shelf larval transport and larval ingress occur 

 through multiple steps (Boehlert and Mundy, 1988; Het- 

 tler and Hare, 1998), effectively decoupling wind-driven, 

 cross-shelf larval transport from larval ingress. 



Similarities in vertical distributions of larval B. 

 tyrannus and exported larval taxa indicate that a great- 

 er proportion of B. tyrannus larvae may be entrained 

 into the Gulf Stream than larvae of other species that 

 use southeast estuaries as juvenile nurseries. Once 

 entrained into the Gulf Stream, larvae are transported 

 northeastward and they either continue to move in the 

 Gulf Stream or are returned to the shelf edge north of 

 Cape Hatteras by warm-core ring streamers or in dis- 

 charges of Gulf Stream water (Hare and Cowen 1991, 

 1996; Churchill et al., 1993; Cowen et al., 1993; Hare 



et al., 2002). Govoni and Spach (1999) reported offshore 

 exchange of B. tyrannus larvae into the Gulf Stream, 

 and Warlen et al. (2002) concluded that some B. tyran- 

 nus larvae spawned south of Cape Hatteras do enter 

 estuaries north of Cape Hatteras in the spring. The 

 mechanisms of northward transport of B. tyrannus have 

 yet to be studied, but transport to the northeast United 

 States shelf edge by the same mechanisms as those that 

 drive exported taxa is possible. 



In marine systems, larval fish interact with verti- 

 cally structured flow with vertical motions and thereby 

 affect their horizontal transport (Cowen et al., 1993, 

 2000; Grioche et al., 2000). Apart from specific trans- 

 port mechanisms, the present study demonstrates an 

 overall link between larval vertical distributions and 

 transport for multiple species. Species that moved in- 

 shore or remained on the shelf were found deeper in 

 the water column than species that were exported from 

 the shelf. Cowen et al. (1993) indicated that as larvae 

 on the northeast U.S. shelf edge move deeper, they 

 become more susceptible to onshore flows. Similarly, 

 Cowen et al. (2000) argued that pomacentrid larvae 

 are distributed at mid-depths off Barbados, and these 

 mid-depth distributions resulted in larval retention 



