They also typically have nine rays in their pelvic fins. Yellowstone cutthroat trout usually spawn from May through early July. The female digs a shallow pit in the gravel of a stream, deposits her eggs as the male fertilizes them, and then covers the eggs with gravel by fanning her tail. The female then digs another pit and the process is repeated. The process continues for two or three days until all of the female's eggs are safely covered by gravel.
Trout usually remain in the tributaries for two to four weeks after spawning.
Eventually, they will make their way back to the main rivers. At Yellowstone Lake, older and larger fish begin the spawning migration first. Males migrate earlier than females and remain longer in the spawning streams. In Yellowstone National Park, there are regulations that protect fish during spawning runs. Due to the absence of fishing pressure, about 26 percent of the spawning fish in Yellowstone Lake populations survive to spawn again.