Transport of fish larvae through a tidal inlet

Abstract

In the South‐eastern USA many species of estuarine‐dependent fishes spawn offshore and their larvae are transported into estuaries. The present study combined physical measurements and zooplankton sampling at the Beaufort Inlet (North Carolina) to determine: (i) whether fish larvae enter the estuary inlet in different horizontal sections of the tidal stream and (ii) whether larvae use selective tidal stream transport (STST) for ingress through the inlet and for movements up the estuary. Larvae of Atlantic menhaden (Brevoortia tyrannus), spot (Leistomus xanthurus), pinfish (Lagodon rhomboides), Atlantic croaker (Micropogonias undulatus), gulf flounder (Paralichthys albigutta), summer flounder (P. dentatus), and southern flounder (P. lethostigma) were sampled over two 25‐h periods (13–14 March, 25–26 March 1996) at three locations across the Beaufort Inlet and in the three main channels receiving water from different locations in the inlet. All species, except Atlantic croaker, primarily entered the inlet on the east side with up to an order of magnitude difference in abundance across the inlet from East to West. The gradient continued in the corresponding channels in the estuary. In most cases equal sizes of larvae were caught in the East and West channels of the estuary. Most larvae were caught at night. A pattern of abundance relative to tide was least evident in the inlet, but STST was evident in the estuary. At the location of greatest larval abundance (Shackleford Channel), the greatest numbers of all species of larvae were caught during rising tides at night. This relationship was not due to passive suspension, since abundance was higher during the faster nocturnal flood tide currents than during to ebb tide currents of equal magnitude. In the Shackleford Channel, southern/gulf flounder and pinfish were distributed throughout the water column during STST, but primarily at the surface. Atlantic menhaden, spot and Atlantic croaker were distributed throughout the water column, and summer flounder were near the surface.