If I would have caught one small enough the snake could swallow, I would have given the fish to it. Snakes can eat prey much larger than their own head diameter, but these trout were too big. After seeing this I searched for info about snakes taking anglers' fish and found some documentation of snakes that died trying to swallow large prey.
Several days after this, I realized I could have sliced off a finger-sized strip of fish and set it out to see what the snake would do with it. If I get to fish this lake next summer and see snakes, I may try it. I find snakes fascinating. This was the first time I have seen in person how a snake can move each side of its jaw independently to move prey down its throat.
I have seen postings on local fishing groups that some mink along the city stretch of the Boise River have learned that anglers are an easy source for a fish dinner. Some evidently have even followed fishermen, waiting for a chance to grab a fish.