Switches can act on individuals, cohorts, or populations. Working conceptual model of eastern Bering Sea walleye pollock survival at different life stages. Relative mortality, important environmental processes and the life stages that they affect are indicated. In our working conceptual model, most mortality takes place in the juvenile life stage, although mortality during the larval life stage could be important in some years. Two factors have been suggested as important mechanisms in regulating eastern Bering Sea pollock year-class strength.
Environmental factors enter our model through their impact on spatial overlap.
Wind drift influences the distribution of animals prior to the juvenile life stage. The strength of vertical stratification of the water column during the juvenile life stage likely is also important. In cold years, the associated winds reduce the affect of this mechanism, and juvenile utilization of inshore regions is more limited. This results in similar distribution patterns of adults and juveniles, potential for more cannibalism, hence a weak year class. Even when adult and juvenile life stages coincide, stratification of the water column can effectively separate adults from juveniles.