You could also get age and genetic information. When I looked at age data for steelhead it varied over time. This was known as far back as Waddell Cr in CA. So, if all you look at is fish collected in the "early" fisheries you have no idea of the age co position of the run. Also, since it has been shown that repeat spawners appear to return at the same time as they did on the first trip you miss the later fish and you may underestimate the actual amount of repeats as the only segment sampled is the one that gets killed.