I actually just read a ministry paper on the average age of adult spawning steelhead on Vancouver Island earlier this afternoon. Think I can find the paper again? Nope it somehow vanished and I can't remember the search I used....
Regardless... they have a list of 20 or 30 diff rivers where samples for age were taken. Most rivers had the largest age class composed of 4 year old fish (most rivers the population was made up of 25% or greater of 4 year fish). Some rivers were made up entirely out of 4 or 5 year old fish, whereas others had very few 4 or 5 year old fish and a whole bunch of 1,2,3 year old fish. If I remember correctly, the Stamp had a large component of 2 year old fish (hence their small average size).
So, some fish return after their first year of salt water. Some fish return after a couple years, and some fish will spawn 3 or 4 times before they finally die (these are the big ones).
It's interesting. The last couple years of the very poor winter steelhead fishing, there have been very few small fish caught from my own observations and friends observations. Generally when fish have been caught, they have been fairly large. I'm wondering if there is some sort of event that is eliminating the 1st and 2nd year class fish right now (offspring of the past couple years) out in the ocean. I would assume the low survival would be during the smolting/going out to the ocean for the first time stage (this would make the most sense as the larger fish seem to be surviving fine returning to the ocean as adults, and coming back a 2/3/4 time).