An eddy is a current that usually moves in a circular path; it may develop where currents encounter obstacles or where one flow passes another. How can we detect an eddy? Eddies frequently occur over the sea valley west of Kodiak Island as revealed by: (1) satellite infrared, synthetic aperture radar and color scanner imagery; (2) buoy trajectories; (3) water property observations; (4) larval distributions; and (5) moored current records.
FOCI studies indicate a tendency for the coincidence of larval patches and mesoscale eddies and that for early larvae, presence within an eddy improves survival. High abundances of walleye pollock larvae often reside in eddies. To monitor the frequency and location of eddies, scientists use high resolution Synthetic Aperture Radar (SAR). During early spring 1992, SAR detected three eddies. In mid-spring, scientists deployed a satellite-tracked drogued drifter in an area of high larval abundance. The buoy made a circular trajectory around a mesoscale feature that likely was one of the eddies observed in earlier SAR imagery. Analysis of water property and shipboard Acoustic Doppler Current Profiler observations taken at the same time confirmed the existence of this eddy. The density of larvae contained in the eddy was estimated to be one order of magnitude greater than in surrounding waters.