Circulation and larval fish transport within a tidally dominated estuary

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Abstract
In March 1996 two surveys of larval fish abundance and water flow were carried out within the estuarine region near Beaufort Inlet, NC. Each survey extended over two full semidiurnal tidal cycles and included measurements of larvae concentration and velocity distribution at several locations. There was a large across‐channel variation in the subtidal flow passing through Beaufort Inlet, with net inflow over the eastern and central portions of the inlet and net outflow on the western side of the inlet. This pattern was consistent with moored current meter measurements of a previous study, and was reproduced by a numerical model circu‐lation forced only by the M2 tide. A net ingress of larvae from the open ocean into the estuary was observ‐ed during both surveys. Most larvae entered the estuary over the eastern and central portions of the inlet, where the subtidal flow was up‐estuary. However, the mean circulation played a minor role in the net movement of larvae into the estuary. Rather, net up‐estuary transport of larvae was principally due to variation of larval abundance with tidal flow; with abundance during flood tide usually far exceeding ebb tide abundance. This mode of transport was likely driven by a behavioural response to tidal flow in which larvae tended to descend to the bottom on falling tides and reside throughout the water column on rising tides.