steelhead here only spawn in the spring, they winter over in the creeks, hence the fall runs and the dark colours in the spring. the longer they are in the rive,r the darker they will be if they spawned in the winter, the survival rate for the newly hatched would be very very low due to water temps being too cold. water must be at least 7 degrees before spawning will take place below that, they go into a dormant state, which is why winter steelheading can be frustrating at times.
in warmer climates, like out in BC where winter temps are above zero, there will be 2 spawning runs. but here in Ontario, only 1.