Walleye Pollock are semi-pelagic schooling fish widely distributed in the North Pacific, with largest concentrations found in the eastern Bering Sea. Their speckled coloring makes it difficult for predators to see them when they are near sandy ocean floors. Walleye Pollock exhibit diel vertical migration, following the seasonal movement of their food. Although Walleye Pollocks exhibit vertical movement during the day, the average depth that they can be found changes with the seasons. Source: https://en.wikipedia.org/wiki/Alaska_pollock