In the case of the browns, the eggs incubate through the winter, hatch during late winter, and the tiny fry emerge from the gravel during the first warm days of spring. This whole process is, of course, temperature dependent. The number of eggs produced depends on fish size. An 8-inch mature brown trout may spawn 200 eggs, while a 10-pound female might spawn over 8,000 eggs. With this in mind, it is important to allow the process to take place undisturbed.
The browns will tend to spawn for a few months in some spots. It is bad form to fish to the spawning trout so keep an eye out for the redds and avoid them. The fish will tend to stack up down stream from the redds waiting to move in. If you see a fisherman near them who is unfamiliar with the sensitivity of the area, a kindly warning will not go astray.
Similarly with rainbows which spawn in the spring. The same considerations apply so watch out for the redds and steer clear to ensure that the trout have the best opportunity to spawn uninterrupted. There are enough natural predators and obstacles to the process without unnecessarily introducing more.