Barotropic tidal and wind-driven larval transport in the vicinity of a barrier island inlet

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 outside 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.

Duke Scholars

Author James Hench Marine Science and Conservation