In both Shelikof Strait and the Bering Sea, eddies play a role in coupled biophysical processes. These features frequently occur over the sea valley west of Kodiak Island as revealed in infrared, synthetic aperture radar, and color scanner satellite imagery [ Reed et al., 1988; Schumacher et al., 1991; Vastano et al., 1992; Liu et al., 1994], buoy trajectories [ Incze et al., 1990], water property and larval distributions [ Schumacher et al., 1993], and moored current records [ Bograd et al., 1994]. The location of eddy formation coincides with the spawning region. Formation of three or four eddies per month during spring [ Bograd et al., 1994] assures that some eggs hatch into an eddy. As a result of limited dispersion, high abundances of larvae often exist in such features. Further, since some eddies tend to remain nearly stationary for periods of weeks, they retain larvae in the sea valley [ Reed et al., 1989; Vastano et al., 1992; Schumacher et al., 1993]. Some eddies have unique chemical properties [ Incze et al., 1989], which may aid prey production and survival of larvae in the eddy [ Schumacher and Kendall, 1991]. Nutritional condition of first-feeding larvae can be reflected by the ratio of ribonucleic acid to deoxyribonucleic acid (RNA/DNA). Concentrations of nauplii, larval gut contents, and RNA/DNA were higher for larvae in an eddy than for those in adjacent waters [ Canino et al., 1991; Bograd et al., 1994].
Results from observations during May 1990 showed a connection between an eddy and larvae [ Schumacher et al., 1993]. Contours of larval abundance coincide with those of salinity, and lie in close proximity to buoy trajectories. Physical data showed little or no exchange of water between the eddy and adjacent waters, permitting estimates of mortality that reflect only predation and/or starvation. The observations yield a daily mortality (4.4%) low compared to other estimates based on observations (6.3%, Reed et al. [1989]; 5-11%, Yoklavich and Bailey [1990]), or from dispersion model simulation (5.9-8.0%, Kim and Bang [1990]).
In the eastern Bering Sea, the presence of relatively small eddies (diameter <50 km) has recently been documented [ Schumacher and Stabeno, 1994]. These are formed in regions of high current shear in open waters, or by interaction of inflowing Alaskan Stream water with topography of passes in the eastern Aleutian Island chain. Eddy formation during periods of inflow through this pass occur in a numerical model of the region (M. Spillane, pers. comm.). Since 1986, 58 satellite-tracked buoys have been deployed in the Bering Sea to support studies of pollock and their environment. In 4 of these years, five regions of high rough counts of pollock larvae were found and buoys deployed in them. In all but one case, the trajectories of the buoys defined eddies. Likewise, the buoys (33) that were not deployed in a patch did not indicate eddies. This association of pollock larvae and eddies may have significant impact on larval survival.