The 20 inch minimum size limit on bull trout came from some life history studies on the region's bull trout (Skagit/Stillaguamish/Snohomish river basins). It was found that there were 3 basic life histories - resident, fluvial and anadromous. What was found was that a 20 minimum size limit would protect virtually all the females in the population through at least one spawning. The resident fish would be protected their whole life, the fluvial (river dwelling) fish would be protect for at least 2 spawnings and the anadromous fish for one or two spawnings. This regulation change went into effect in 1990 was design to address what was thought to be an over fishing problem (many of the fish were being harvested as both sub-adult and adult fish).
It appears that the change was successful in addressing the over-harvest problem as evidenced by significant increases in spawning abundance with the degree of response apparently limited by the amount of spawning and rearing habitat for the small juvenile bull trout. Following the regulation change there was a several fold increase in spawners on the Snohomish system and on the Skagit the increase was more than a 20 fold increase in the numbers of fish on the spawning grounds.
For those interested in a thumbnail sketch of bull trout 101 the following link may be of interest -
It may be time to re-visit bull trout management in those basins where harvest is currently allowed though it may be well to remember that in those basins where bull trout harvest is not allowed fishing for them is prohibited. While that may not be a problem to some the is somewhat of an angler ethical question for those that want to target them.
Congrats on a very nice fish! Which with its adipose fin a wild one.
The fish in question is not a half-pounder. The center of the half pounder steelhead life history is the Klamath river basin with them common in northern California and southern Oregon. A half pounder is a steelhead that after smolting spends 2 to 4 months rearing in the estuary or near shore areas only to return as immature fish to over winter in freshwater before returning to the salt for additional growth before returning as an adult steelhead. This behavior is very similar to what we see here on the larger north sound rivers with sea-run cutthroat and bull trout; that is immature sub-adult fish after a short period of marine residency return to freshwater (may or may not be their natal system) to over winter. While half-pounder have been seen in Puget Sound such fish are exceedingly rare.
Daniel's fish clearly is in a post spawn condition indicating that it is an adult thus not a half-pounder. There are 3 life histories that might account for an O. mykiss adult of that size that would be found in a north Sound river. The first would be a 1 salt summer steelhead. Such fish are usually 24/25 inches long though they can vary from as little as 19 inches to more than 30 inches long. Some years quite a few of those one-salt fish in our local rivers are in the 19 to 21 inch range. This time of year a fresh run fish would be chrome bright; the spawning of the wild summer fish is from March to about mid-May so encountering an post spawn adult this time of year is not very likely.
The second life history would be winter fish that returned as a "jack". A male fish that matures a year early returning typically at a size of 15 to 17 inches. These fish are capable spawners and occasionally will survive to return to spawn a second time. Such fish would often be in the size range of Daniel's fish and would expect a small handful of such fish to be found in a health wild population of significant abundances.
The third life history as all ready referred to is the resident form/rainbow. Resident rainbows are becoming more common on some of our north Sound rivers and such fish can reach the size of the one pictured more often than some would think. Our resident rainbows in our steelhead rivers typically mature at age 4 at a length of 14 or 15 inches. They experience much higher post spawn survival than their anadromous cousins (repeat spawner rates at 50% or so). They will often grow 2 to 3 inches between spawning and may survive to spawn 6 or more times achieving lengths of more than 24 inches in the process.
It is most likely the fish in question is a resident rainbow but without a scale sample it would be impossible to say with certainty.
Not that I post much on this this site. Nor do I claim to know as much as you would on this subject ever. I can only go off of what I have seen happen on the sky over the last 5 years or so more than I have ever seen in my past 25+ years on it. I agree that the size and the range of the fish would be consistent with a jack and the term "half-pounder" would be incorrect. However, just the other day I landed a fish of almost exact size and weight, native, and two toned chrome bright. I have also seen and hooked more and more fin clipped versions of this fish in June. I also had an experience on the Cowlitz last summer all fin clipped fish that looked the same. (they were not the cutts in there, we got those to)
The coloration of this fish would indicate a "resi" but that doesn't indicate summer run or not. Once upon a time when we fished into April, it wasn't completely unheard of to run into an early summer run. If this happened to be one of those fish, it most likely would have the color of a fish that has been in the river for a while. I've seen it in June with other wild fish (pictures to prove it if needed).
A scale sample would be the only way to tell for sure. But the rainbows that I have caught on that river tend to have much more bulk than that fish. I'm hoping that this is a good sign to come with our wild fish populations. I vote Jack.