Great Lakes river mouths are transition zones for salmon

It’s easy to understand why Great Lakes salmon and trout gravitate to the places where streams or rivers flow into the Great Lakes in late winter or early spring. The lake’s water may be hovering near the freezing point while the water flowing into the lake is often warmer by 10 degrees or more. It’s more comfortable for both predators and prey. So why, in late summer and early autumn, do salmon gravitate to the waters near Great Lakes pierheads and the mouth of some Great Lakes tributaries? The water temperature in these nearshore waters is seldom salmon-suitable and even if there are baitfish in the area, the salmon are no longer actively feeding.