Even at first glance, you can see the absence of spots, eliminating most.
Should be easy at that point.
Exactly Canso
Years ago during my AFS days with DFO I taught FN people basic salmonid biology and fish identification was a component. At the time I was shocked that these people could not differentiate between different species – to them, mainly upper Fraser and Skeena watershed bands, they were just salmon.
Frustrated, I tried using the process of elimination of species ie. no spots eliminates coho, pink, chinook, steelhead and other trout/char, leaving just 2. As there are virtually no chums in these upper watersheds it became easy.
I also found the spotting on tails to be another easy way to eliminate species and when adding this information to species distribution, size and coloration, general run timing and life histories and it all came together.