I have a dilemma. What I am looking for is the information to make the right decision. The main information I need is; at what size are stunted rainbow trout about to reproduce reliably.

The Background (a.k.a. The Verbiage)
When I can, I like to fish very small creeks, especially creeks that have the descendants of stockers. These are usually rainbows. I call these creeks "bathtub creeks" because most of the fish are found in tiny pools that look to be no larger than a standard bathtub. Note that some work with a tape measure arithmetic usually shows that they are the size of a few bathtubs, but you get the idea. (I am an agile angler and can exaggerate in either direction.) Also the flow is often about that which a tap could produce. One works cautiously along the bank and then stalks and observes the pool before casting. Perhaps every hundred yards or so, one comes to a casting opportunity. In the past, I fished these with a friend or two and we took turns on the pools.

The Setting
We were working upstream on a creek that one could step across in many places, but the stream was a gem. It hadn't been stocked for a while and the trout were descendants, several times removed, of the hatchery fish. There were a number of fingerlings in the stream. The other fish were mostly stunted bream (sunfish) to about 4" long, some little minnows, and something that might have been sculpin. We were young and never paid much attention to the latter. It was my turn as we approached the pool. The stream flowed, and still flows, through a tiny valley between two ridges. One was very steep with a fair amount of exposed stone and the rest covered by trees. The other, although still steep, was not as steep and was mostly pasture. The valley itself was prone to the occasional flash flood and left in timber. Most of it had been clear cut two or three decades before. The stream meandered through this rather nice setting. Most of the trees were too small to harbor widow-makers, dead limbs large enough to do serious injury if they fall on one.

The pool that I faced had an old, broken tree whose roots constituted the left bank. Erosion had partially eaten away underneath the tree. To the right at the bottom of the pool was a small sand and gravel bar. The deeper water was on the left and left the pool via a gravel riffle. Just to the right of the pool, some thorny vines worked up 3-4 saplings and provided a screen for my spotter. We knew that a big, cannibal rainbow lived in that pool and it was my turn to try for it, again.

My spotter worked carefully into position and we waited until he spotted the fish. My spotter reported that it has just eaten a minnow or trout fingerling. I tied on a small streamer and cast upstream of my quarry. The cast was acceptably accurate, as it was short. I couldn't see the fish so I waited until my spotter told me to strike. I did. In a short while, we were looking at a fat rainbow that went about 14 inches, a true monster for this water. Now we had to decide what to do with it. We usually practiced a version "catch and release" that we called "throwing 'em back". This fish was clearly big enough to eat and it was eating rainbow fingerlings. We wanted more generations of rainbows to grow and thrive so that the population would remain healthy through genetic diversity.

Given that our intent was primarily for that creek's rainbow trout population to be of great enough numbers to provide very long term stability, should we have kept the trout so that it wouldn't eat so many fingerlings? Should we have let it so that it would breed? That is my question. Many years later, I still don't know.

To be fair with you, I'll come clean. (Please pardon the pun.) We kept the fish.

Thanks,
Ed