A Possible Eddy Retention Mechanism for Ichthyoplankton in Hecate Strait

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Abstract
The cause of the high rate of production of groundfish in Hecate Strait is uncertain. It is likely that the large, shallow areas of the Strait contribute to the high productivity because of their suitability as juvenile habitat. In winter, however, when many groundfish species spawn, a strong current flows northward through the Strait into Dixon Entrance and likely carries many of the pelagic larvae out of the Strait. A recent study shows that the recruitment rate of Pacific cod varies inversely with this current, which is to be expected if the larvae are swept out of the Strait by the flow. We examine current and wind data from a variety of field programs in Hecate Strait, and find evidence for a return flow toward the southwest in Hecate Strait, counter to the wind-driven transport. This return flow is driven by the set-up of sea level along the Strait by the wind, and its strength increases with the intensity of southeast storm winds. We believe the return flow will recirculate a significant fraction of the larvae in the Strait, increasing their residence time sufficiently to allow settling out, thus enhancing recruitment.

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