Larval transport during winter in the SABRE study area: resultsofacoupledverticallarvalbehaviour±three-dimensional circulation model JONATHAN A. HARE, 1 JOHN A. QUINLAN, 2 FRANCISCO E. WERNER, 2 BRIAN O. BLANTON, 2 JOHN J. GOVONI, 1 RICHARD B. FORWARD, 3 LAWRENCE R. SETTLE 1 AND DONALD E. HOSS 1 1 NOAA National Ocean Service, Center for Coastal Fisheries and Habitat Research, 101 Pivers Island Road, Beaufort, NC 28516-9722, USA 2 Department of Marine Sciences, University of North Carolina, Chapel Hill, NC27599-3300, USA 3 Duke University, School of the Environment, Marine Laboratory, 135 Pivers Island Road, Beaufort, NC 28516- 9722, USA ABSTRACT A three-dimensional circulation model was used in conjunction with larval fish vertical behaviour models to study the interaction between larval vertical distribu- tion, 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 demon- strated 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. INTRODUCTION Cross-shelf transport is critical to the larval survival of many marine fish species that spawn offshore, yet utilize nearshore juvenile habitats (Boehlert and Mundy, 1988; Werner et al., 1997). Most identified cross-shelf larval transport mechanisms involve interactions be- tween vertical distribution of larvae and vertical structure of cross-shelf currents. These interactions, however, are embedded within three-dimensional flow, and in most continental shelf systems, the along-shelf component of flow exceeds the cross-shelf. On the California shelf, seaward advection of surface water, caused by wind driven upwelling, results in offshore transport of surface dwelling larvae (Bailey, 1981; Fiedler, 1986). Maximum cross-shelf flows are *10 km day 71 , yet maximum along-shelf flows are *25 km day 71 (Dever, 1997a, b). Likewise, during summer on the Mid-Atlantic shelf, larval fish move onshore in mid-level intrusions of water (Cowen et al., 1993), which are in part, driven by upwelling-favourable winds (Flagg et al., 1994). Cross- shelf displacement in these intrusions is 3±5 km day 71 , while along-shelf displacement is 5±15 km day 71 (Flagg et al., 1994). Although two-dimensional, cross-shelf con- ceptualizations are very useful, the greater magnitude of along-shelf flows requires a three-dimensional framework to more fully understand cross-shelf larval transport. Three-dimensional numerical circulation models provide a powerful approach to study larval transport. Models have been used to examine large-scale (410 4 km) larval transport in the North Atlantic (Bartsch and Coombs, 1997) and North Sea (Bartsch, 1993), as well as meso-scale (10 3 ±10 4 km) larval trans- port in the German Bight (Bartsch and Knust, 1994), on Georges Bank (Werner et al., 1993), and in the Gulf of Alaska (Hermann et al., 1996a). Links between modelled larval transport and interannual recruitment variability have been examined for sand eels in the North Sea (Berntsen et al., 1994) and pollock in the Gulf of Alaska (Hermann et al., 1996b). These studies, and colleagues, provide substantial insight into larval transport processes in specific systems. FISHERIES OCEANOGRAPHY Fish. Oceanogr. 8(Suppl. 2), 57±76, 1999 1999 Blackwell Science Ltd. 57 *Correspondence. Dr J. A. Hare, NOAA National Ocean Service, Center for Coastal Fisheries and Habitat Research, 101 Pivers Island Road, Beaufort, NC 28516-9722 USA. Tel. +1 252 728 8732; Fax: +1 252 728 8784; E-mail: Jon.Hare@noaa.gov Received for publication 27 April 1999 Accepted for publication 15 May 1999 Copyright remains the property of the US government Ahed Bhed Ched Dhed Ref marker Fig marker Table marker Ref end Ref start Paper 17 Disc