Steelhead smolt vs. trout?

o mykiss

Active Member
At the risk of exposing my own ignorance, can anyone tell me a reliable way to tell the difference between a resident rainbow and a steelhead smolt? (Let's assume we're fishing on an anadromous fish-bearing stream.) I have caught what I thought were RBs on the Snoqualmie (below the falls), Skykomish and Tolt. (I'm not talking about the little buggers that will hit anything, which I have always assumed to be smolts and try to avoid if they're coming after my fly.) On the one hand, I heard once from a local steelhead guide that there aren't really resident rainbows on the anadromous fish-bearing Puget Sound rivers, but I have a hard time buying that because I have read in fishing guides and in the WDFW's own literature that there are RBs in these waters. I am strictly C&R, so I'd like to think I'm not doing any real harm to a fragile resource, but if I am getting into smolts it would be nice to know know it so I can move on to other opportunities.
The reason they have 14" minimums is to eliminate that problem. On anadromous waters, I assume any rainbow under 14" to be a smolt (they'll probably be under 12"). Usually you know a 16 or 17 incher or greater is a rainbow. Most of your steelhead will actually be 24" or greater usually though the regs say 20". There are bows in all these rivers. Also, the resident bows will usually be fat and broad shouldered wher the steelies will be torpedos. Of course, if they are missing the adipose fin or another than yo can be sure they are smolt.

Rob Blomquist

Formerly Tight Loops
The "factoid" about there not being any resident rainbows in rivers with steelhead is merely an old fisheries biologist's tale.

All anadromous fish have some tendency to residualize. These residual steelhead will be seen as rainbows in the rivers. Similarily, coho, chinook and sockeye residualize in Lakes Washington and Sammamish, where food is plentiful enough that some fish don't feel a need to leave. Kokanee are residual sockeye, and sockeye have a strong tendency to stay in their rearing lake.

Now, as how to tell rainbows from steelhead apart? Well, rainbows look like rainbows, and steelies like steelies. Its that easy. If they don't leave the river system as smolts (those little guys we don't want to hurt) then they are rainbows.

And BTW, I caught a chunky little 10" rainbow that took a steelhead pattern 2 years ago in January while fishing for steelhead in the confluence pool of the Tolt river joining the Snoqualmie.

If it's too big to be a smolt but too small to be a steelhead it's rainbow :BIGSMILE
the clue is appearance: rainbow can be almost as big as steelhead where is enough food but carry it's pink stripe thru all life (and body proportions slightly differ).
I had no luck with such monsters :BIGSMILE but 12-13" rainbows occurs in Skykomish system
Well I imagine you're not too confused about the difference between adult rainbows and juvenile steelhead. The question seems to be how to tell the difference between juvenile (read small) residents, and juvenile steelhead. Unfortunately, the short answer is you can't, not in the field anyway, unless the steelhead is actually "smolting." (That is, preparing to make the transition to saltwater; its scales will be fine and silvery, sluffing off easily when handled.)

What most of us refer to as "smolts" are usually steelhead parr. They generally won't be bigger than 6-8 inches, with rare individuals up to about ten inches. Some notable exceptions can occur in the southern range -- CA and far-southern OR -- where some coastal steelhead streams can go subterraneon at their mouths for years at a time. The juvenile steelhead involutarily "residualize" in the somewhat brackish lagoons, reaching lengths commonly up to 16". Meanwhile of course, the stream is gathering no annual runs of anadromous spawners. Fairly consistent fisheries can develop for these lagoon "trout." When conditions finally allow the mouths to break open, the "trout" almost immediately disappear, and the stream starts gathering genetically distinct anadromous steelhead again.

One of the many things those cases illustrate is the amazing life-history flexibility of steelhead/rainbows. Other posters on this thread have noted the tendency of juvenile steelhead to residualise. But it works in reverse as well. "Resident" rainbows can provide a genetic "bank" for sympatric steelhead populations, when resident rainbows and steelhead spawn together (documented in many areas of the range). Also, resident rainbows (even if both parents were residents) can and will spontaneously smolt and become anadromous (lots of cases all over Washington). This can be an important factor for populations that could use any kind of a demographic leg up (don't suppose there are any of those around here, huh?).

So the long and short of it is that any juvenile rainbow under 8" in an anadromous stream-reach is a possible (or potential) steelhead. The chances go up in rivers with a large ratio of steelhead to resident-rainbows (like most westside Washington streams).

I'll don the professor's cap (he should come with a companion emocon that he's putting to sleep), even though I don't know that I've answered your question. I guess I'd have to say that if you're into nothing but sub-8s with adipose fins on the North-Fork Sky, or the Tolt, or someplace similar, and catching juvenile steelhead bothers you, it wouldn't hurt to move on. Now of course we could get into a whole other discussion of when, where, how, why, and if it's OK to C&R juvenile steelhead. Like everything else, the answers certainly wouldn't be cut and dry. :pROFESSOR

o mykiss

Active Member
I have occasionally run into the small guys with parr marks, have always assumed those to be little steelhead and have left them alone if they start hitting my fly. But I have also caught what looked like trout 10" and up (I'd say the largest one I've caught was in the 15" range off Buck Island on the Sky, but also fish in the 12" - 14" range very occasionally on the Tolt), so it's really that size fish that I'm confused about. You mentioned that smolting steelhead will have fine, silvery scales that are easily sloughed. That is one clue for me to look for next time. Can you, as vic_sea indicated, distinguish between resident bows and juvenile steelhead based on the presence or absence of a pinkish stripe on the sides?
You know, there are probably some general morphometric markers that may hold true in a broad sense, and vic's seemed generally accurate to me (I've been around for awhile, and I like to think I can make an educated guess), but the variability among and between populations and individuals is so great that I don't think you could call any field-sign accurate, at least not scientifically, particularly in juveniles. Now like I said if you're talking about fish bigger than 8-10", it seems a pretty safe bet that they're rainbows. They're too big to be anadromous juveniles, and I don't think that any of our rivers have very high incidence (if at all) of the "half pounders" they see down in OR and CA.

When you're trying to ID a true "smolt" remember that steelhead spend 1-3 years in fresh water, and the "smolting" phase is very short, I think only a few weeks (I know there are other "professors" on this board who know for sure).


New Member
Look a steelhead smolt is a rainbow trout until he goes out to sea, then he is a steelhead. Its like sea run dolly varden that you can't tell if it's sea run or not. The way to solve any problems is DON'T KEEP ANY RAINBOWS!!!! Unless they are from stocked lakes.
Tight Lines From Alaska

o mykiss

Active Member
I'm down with letting all bows go (I did say I'm strictly C&R, after all). Thing is that unfortunately down here in WA the steelhead are in bad enough shape that you hear people occasionally question the ethics of "targeting smolts". It was that kind of ethical question that got me thinking about whether there's a way to tell a difference. I don't plan on stopping fishing in local anadromous fish-bearing streams (unless they're closed, of course) - just wondering if there's anything I can reasonably do to avoid being called "unethical". Not that I want to ignite that debate.
Well I ain't to shy about my ignorance. But if your practicing C&R and hookin' less then ten inch fish move on and try for 15" fish. Ya sure don't sound unethical to me. ya seem quite sensible. Be glad ya ain't here on the east side where smolt can be a lot bigger then 10 inches. :THUMBSUP
Nobody seems to be arguing against releasing all native rainbows, resident or anadromous. It seems to me that Mykiss was acknowledging that C&R is not always enough, that some fish shouldn't be fished for AT ALL, and he was wondering how to tell when or if he was over that line. I applaud him for that.

I'm not ready to talk about the comlexities of when/if/where it's OK or not OK to C&R juvenile steelhead. I was just trying to give Mykiss information (as I understand it) he could use to make judgements according to his own sense of ethics, which seem to me reasonably highly refined.