Parker,
Bob's right regarding genetics. Large animals produce more large offspring than small animals. Same with salmon and steelhead. A corolary to the steelhead example is Puget Sound chinook. The average age at maturity used to be 5 years. Years of gillnetting pushed that to age 4 and a smaller average size. Now there seems to be an ever larger proportion of the adult return coming back at age 3 and yup, you guessed it, even smaller average size again.
The key difference with the lower Quinault is the overall harvest rate on steelhead, coupled with the continued mixing between the natural and hatchery populations. The effect of you retaining one large steelhead on the population is decidedly small. But for that matter, the effect of me taking one large steelhead from the Sauk River population is decidedly small. But cummulative effects do count, and as a matter of conscience, I don't retain wild steelhead from any population. True, I haven't fished the lower Quinault, but when I do, I won't be retaining those steelhead either. That's not why I go fishing.
I believe it may be true that the cummulative effect of recreational and net fishing combined may have a negligable effect on the Quinault River steelhead. So you can keep whatever fish you catch with a clear conservation conscience I suppose. But if you choose to release the fish, consider the statement you're making about yourself. Even though the interests of conservation may not require your action, you choose release over retention as a measure against the uncertainty of loss to a very unique steelhead population.
Not exactly to the point, but I figure when the cost is small, it's a good time to be big. Releasing wild steelhead is easy.
Sincerely,
Salmo g.