An Overview of Shelikof Strait FOCI

1. Circulation is dominated by the Alaska Coastal Current which is one of the strongest and most persistent currents found along the coasts of North America. While the majority of volume transport throughout the water column is directed seaward through the Shelikof sea valley, approximately 75% of the water in the upper 50 m appears to stay on the continental shelf.
2. There is a persistent, relatively weak flow of slope water into the sea valley. This feature is a nutrient source which lies under and (at the near surface) to the south of the ACC. Interannual variations in bottom-water properties have been related to anomalies in the circulation in the Gulf of Alaska.
3. Baroclinic instability and wind-driven flow out of Wide Bay are mechanisms which form features that tend to retain larvae on the shelf. The role of these features in larval retention and the potential impact on secondary production/larval mortality are ongoing topics of research.
4. Strong spatial variations in the wind field can result in an area of convergence of the surface-layer currents. The scale of this feature is consistent with the observed size of a patch of pollock larvae.
5. During the 1980's, several adjacent strong year classes (1975-1979) moved through the Shelikof Strait population of walleye pollock causing a variation in numbers of adults from 6.0 to 1.3 billion. Until recently, only weak or moderate year classes have occurred since 1979. Thus during our studies we have not had the opportunity to observe conditions leading to a strong year class. The interannual variations in the physical environment and in the early life history of pollock have resulted in only minor changes in year class size. Focus on the strong year class of 1994 may lead to advances in our understanding.
6. There is little interannual variation in the timing and location of pollock spawning and egg and larval development within the Shelikof Strait system. Spawning occurs primarily in early April over the deep trench near Cape Kekurnoi. The eggs reside mainly below 150 m in the water column and are advected little during their 2-wk incubation period. The larvae develop in the upper 50 m of the water column and are advected to the southwest as they grow at about 2 mm/d during late April and May. During this time the larvae are often in large patches that have been found entrained in eddies in lower Shelikof Strait. Entrainment increases their residence time in the area and lessens their chances of being advected offshore.
7. Observable growth of surviving larvae varies little. Condition of larvae varies with season and location. Sufficient food may be unavailable to larvae early in the spawning season. Larvae in eddies seem to be in better feeding condition than those outside eddies.
8. Year class size seems to be largely determined by the end of the larval period, although events during the following summer may reduce the year class also. Storms during the early larval period may be particularly detrimental to larval survival, although the mechanism is not yet clear. An index of storminess in the Gulf of Alaska may provide a way of predicting year class size.