In 1962, Ontario fisheries scientist Richard A. Ryder began 15 years of research on walleyes. Ryder sought to prove that light was a primary feeding trigger for these fish.

One aspect of Ryder's work showed that the rate of change in light is the most important trigger causing walleyes to feed. Ryder found that fishing was better at certain surface light levels -- for instance, as the sun's rays became more oblique (about 1 1/2 hours before sunset to a half hour after).

Ryder concluded that amount of light has a bearing on walleye feeding, and under optimum light conditions, fish might leisurely feed throughout the day. But the main trigger for intensive feeding appears to be the fast rate of change in light at dusk, and to a lesser degree at dawn.