This is one way to tell the difference between Chinook and Coho. Usually you can tell the difference before you have them in the boat by the way they fight.
Now if you know the purpose of the pyloric caeca, I'll be VERY impressed.:flowered:I prefer to open them up and count pyloric caeca myself that's a sure fire way to tell them apart. If it's under 100 it's a coho. It just gets a little tricky on the release.
But in seriousness, the color of the mouth as a whole can be misleading. The proper question to ask is what's the color of the tissue where the teeth erupt from the jaw? If it's black it's a chinook, white coho.
Spotting is more of a generalization. I've seen coho with some spots on the bottom half of the tail.
Lots of subtle variations on size shape and location of spots.
The definitive criterion that will be used to enforce the identity of the fish is the gumline. Nothing else counts.
Look a the color of the gumline.... as the poster above said, particularly the tissue where the teeth erupt.
If it's light (light grey or white).... it will be enforced as coho.
If it's dark (graphite or black).... it will be enfoced as chinook.
The other most striking feature on the lower jaw of a coho is the distinct alternating dark/light/dark banding along the edge of the mouth. It is unmistakable.
Lower jaw of coho salmon. Note the distinct banding pattern of dark to light to dark.</SPAN>
Diagram and two photos showing coloration of lower jaw of chinook salmon.
Note that the coloration at the base of the teeth is consistent with the area inside and outside i.e. no distinct banding coloration although colors can vary substantially.</SPAN>
Might be true for some fisheries like the Columbia but not all. Some while back I was "forced" to change my activity on the Rogue after watching a couple of dozen 40# chinook jumping in front of me. I watched several fishermen land fish and was able to actually weigh them and the smallest was 38# largest 45#. Many limits (2 nate or hatch) caught in front of me.that aint no joke, they also jump acrobatically, where as chinook might splash but would rather stay near the bottom. at least in tidewater.