You are hereSalmon Ecology
The competition for nesting sites encourage salmon to expand the range of their habitat. And the natural tendency of some spawners to stray from their birth stream also enabled them to re-colonize rivers as the ice sheets retreated at the end of the ice ages. At the peak of the last ice age, the northern edge of salmon habitat was Southern California and as the ice sheet over North America melted, they migrated northward until reaching the Arctic Sea. This dynamic also functions when they re-enter restored rivers and is likely to happen when water flows back into the dry areas of the San Joaquin River.