The circulation over the continental shelf off the southern Middle Atlantic Bight (MAB) and northern South Atlantic Bight (SAB) is examined for the fall and winter periods. Observational data are compared with results from a three‐dimensional numerical model to identify the dominant processes on the shelf. By considering wind‐forcing, tides, and a specified upstream inflow (into the MAB), the observed and modelled flow fields are in close agreement in the mid‐ and inner shelf regions. The resulting larval drift indicates a seasonal dependence of transport pathways from spawning grounds to estuarine nursery areas for menhaden larvae and other offshore‐spawning estuarine‐dependent fish. Specifically, the physical oceanography of the MAB and SAB during the fall and winter months suggests a north‐to‐south shift in spawning areas providing recruits to the Carolina estuaries, in agreement with the observed migration of the spawning populations.

A three‐dimensional circulation model was used in conjunction with larval fish vertical behaviour models to study the interaction between larval vertical distribution, advection and the outcome of larval transport along the central portion of the east coast of the United States. The circulation model was forced by tides, a northern boundary inflow, and winds. Vertical behaviour models were developed for Atlantic menhaden (Brevoortia tyrannus) and spot (Leiostomus xanthurus). The purpose of this modelling effort was to investigate the transport pathways of Atlantic menhaden and spot larvae from offshore spawning grounds to estuarine nursery habitats. The coupled circulation and behavioural model demonstrated the importance of along‐shelf transport in what is generally thought to be a ‘cross‐shelf’ problem. Cross‐shelf transport was associated with bathymetric features, such as shoals. Both physical (e.g. wind) and biological (e.g. changes in larval behaviour) events were responsible for many of the observed patterns in larval transport. Overall, larval transport was determined by circulation but was modified by larval vertical distributions.

Fish species such as Atlantic menhaden (Brevoortia tyrannus) must often transit relatively small barrier island inlets to move from their continental shelf spawning grounds to estuarine nurseries, where they spend their juvenile phase. Physical transport through these inlets is strongly influenced by tides, winds, local geometry and bathymetry, and can be very different from that occurring on the shelf. In March 1996, an extensive multidisciplinary field experiment was conducted to identify larval transport pathways in the vicinity of Beaufort Inlet, NC ( Blanton et al., 1999 ; Churchill et al., 1999 ; Forward et al., 1999 ). One of the most interesting results from the field study was significant spatial inhomogeneity in the larval catches ( Forward et al., 1999 ). This paper describes a computer modelling study of tidal and wind‐driven circulation and accompanying larval transport characteristics in the vicinity of Beaufort Inlet. Primary conclusions are as follows: (i) tidal currents are quite effective at creating net larval transport into the inlet; (ii) in the absence of wind forcing, to explain the spatial distribution of larval catches observed in the field experiment, the primary source of larvae must have been to the east of the inlet; (iii) the spring/neap cycle accounts for a variation of approximately 40% in larvae ingress; (iv) only a few wind directions enhance larvae ingress over the case of purely tidal forcing—wind blowing toward the north enhances ingress at the surface, and winds blowing toward the south and the east enhance ingress at the bottom; (v) if larvae are evenly distributed in space out‐side the inlet, then strong east wind (such as 10 m s−1) can cause larvae to move through the inlet in a way that is consistent with the larval catches in the field experiment. However, local wind records revealed that no significant eastward‐blowing winds occurred during or immediately preceding the field experiment.

Atlantic menhaden (Brevoortia tyrannus) is an estuarine‐dependent fish that spawns in coastal waters of the Middle and South Atlantic Bights. Circulation modelling studies of larval transport suggest that recruitment of larvae into the Albemarle‐Pamlico Estuarine System, North Carolina, is linked to dynamics on the shelf from New York to South Carolina. Field‐collected menhaden egg data (from MARMAP and SABRE) define a range of temperatures within which menhaden eggs have been found. In this study we refine the transport model‐predicted spawning grounds for the 1994–95 season by using satellite‐derived sea surface temperature data to highlight regions that are outside the observed spawning temperature range. We also use transport pathways leading from source locations to the estuarine system to characterize the temperature field experienced by particles/larvae during their spawning‐ground to inlet transit. The modelled nearshore location of source regions agrees well with MARMAP and SABRE egg data, and points to the importance of understanding biological and physical linkages between the Middle and South Atlantic Bights. The combination of modelled transport and synoptic temperature maps can provide useful guidance to future sampling efforts as well as help refine our understanding of menhaden ecology.

The circulation and transport of suspended particulate matter in the Caravelas Estuary are assessed. Nearly-synoptic hourly hydrographic, current (ADCP velocity and volume transport) and suspended particulate matter data were collected during a full semidiurnal spring tide, on the two transects Boca do Tomba and Barra Velha and on longitudinal sections at low and high tide. On the first transect the peak ebb currents (-1.5 ms-1) were almost twice as strong as those of the wider and shallow Barra Velha inlet (-0.80 ms-1) and the peak flood currents were 0.75 and 0.60 ms-1 , respectively. Due to the strong tidal currents both inlets had weak vertical salinity stratification and were classified with the Stratification-circulation Diagram as Type 2a (partially mixed-weakly stratified) and Type 1a (well mixed). Volume transports were very close, ranging from-3,500 to 3,100 m 3 s-1 at the ebb and flood, respectively, with a residual-630 m 3 s-1. The concentration of the suspended particulate matter was closely related to the tidal variation and decreased landwards from 50 mg.L-1 at the estuary mouth, to 10 mg.L-1 at distances of 9 and 16 km for the low and high tide experiments, respectively. The total residual SPM transport was out of the estuary at rates of-18 tons per tidal cycle. R E S U M O A circulação e o transporte de material particulado em suspensão no Estuário de Caravelas são pesquisados. Dados quase-sinóticos hidrográficos, de correntes (velocidade e transporte de volume com ADCP) e de material particulado em suspensão, foram medidos em intervalos horários durante um ciclo semidiurno de maré de sizígia, em duas seções transversais na Boca do Tomba e na Barra Velha e também em seções longitudinais na baixa-mar e na preamar. Na primeira transversal as correntes máximas de vazante (-1,50 m s-1) foram quase duas vezes mais intensas do que na seção transversal mais larga e rasa Barra Velha, (-0,80 m s-1) e as maiores velocidades das correntes de enchente foram de 0,75 m s-1 e 0,60 m s-1 , respectivamente. Devido à grande intensidade das correntes de maré, nas duas seções transversais a salinidade apresentou-se fracamente estratificada, sendo classificadas com o Diagrama Estratificação-circulação do Tipo 2a (parcialmente misturada e fraca estratificação vertical) e do Tipo 1a (bem misturada). Os transportes de volume foram muito próximos, variando de-3.500 m 3 s-1 a 3.100 m 3 s-1 , na vazante e na enchente, respectivamente, com um transporte de volume residual igual a-630 m 3 s-1. A concentração do material particulado em suspensão (MPS) esteve fortemente relacionado à variação da maré, decrescendo estuário acima de 50 mg.L-1 , na boca do estuário, para 10 mg.L-1 para distâncias de 9 km e 16 km nos experimentos na baixa-mar e preamar, respectivamente. O transporte residual de MPS foi estuário abaixo com uma taxa estimada em-18 ton por ciclo de maré.