My own take on this, unscientific as it may be, is that we just really don’t know for sure how a steelhead is attracted to our flies, or why they decide to eat them. From some occasional opportunities I’ve had to be able to observe steelhead responding to my fly (or watching them respond to other anglers flies), I am mostly convinced that the mood of the fish is the biggest variable in the equation. I definitely do think certain size/color combinations can make a difference, but I’m not sure we will ever be able to unequivocally state the reasons why, and thus extrapolate a strategy that we can use in similar circumstances expecting similar results.
I think there are just too many factors that are in play regarding a steelheads mood to really know. We’ve probably all come across those fish that are just so aggressive it seems likely they would have chased down and destroyed practically any fly, regardless of color or flash, or profile, etc. Of course there are plenty of times where the opposite is true; where they will actively ignore or avoid pretty much every single offering you put in front of them. The thing that always blows me away is when a fish that seems to have severe lock jaw will change its mind suddenly and pounce on a particular offering. Was it the color of the fly, the seductive movement, just the right size, was the fish finally stimulated by the perfect presentation? Or did their mood simply change? I’ve witnessed it a few times, unfortunately it hasn’t usually been my fly that got lucky.
There was one very interesting experience I had once fishing for Coho/Silver salmon: I was fishing to a good sized pod of fresh fish but neither my father or I was having any luck getting one to grab. The water was a tad clear, so it was easy enough to watch their reaction (or lack thereof) to our flies. We had both pretty much focused our efforts on smallish sized flies, without too much flash, due to the low water conditions; but after several fly changes and no aggressive reactions we started trying mid sized flies, larger flies, flies with more flash, flies with more movement, etc etc. There was one fish in particular that I had watched swerve away from my flies numerous times, as I had nearly bumped his nose more than once. At this point we were mostly going through the motions, hoping maybe a few more aggressive fish might move into the pool with the incoming tide, and I knew it had gotten beyond desperate when I tied on a fly I had almost zero confidence in. I tied on a modest sized GBS (one that I had tied with an equal lack of enthusiasm, creativity, or optimism), made a cast or two, when I literally saw that fish turn his head sharply as my fly swam a few feet past him. I watched as the fish swam all the way across the pool, gaining speed as my fly came to the hang down below me. Somewhat stunned, I started stripping the fly up the shoreline to keep it moving and hopefully keep the fish in hot pursuit. The fish was racing straight up the shallows along the shoreline, about half out of the water at this point and quickly closing the distance on my fly. I’ll never forget seeing him open his jaws and explode on my my fly just as I’d run out of line to retrieve! I just couldn’t believe the sheer focus and tenacity of that fish to destroy that boring, lame fly! We had almost no other action the whole day!? We still laugh about it today, as my father was able to see the whole thing unfold almost as clearly and thought it looked more like I’d pissed the fish off and it was racing over to attack me instead of the fly. Who knows why it changed its mind so dramatically?