I don't think they were fly fishing. That's regarded as "sissy" in Wyoming, I think. Y'all are invited to rush in and correct me if I'm wrong!! I think they were using live bait, which would just "fly" off the hooks if they were fly fishing. Plus, they were probly fishing in streams where the line doesn't have to go a great distance. Streams and beaver ponds, I would think.
Looking at some of the pics from the movie this morning, I notice how often there's something metal lying on the ground, either the shotgun, ax, or saw. I wonder whether these items are different for a purpose in the various scenes. Like in the "I ain't queer" scene, the gun is lying on the ground, pointing toward the mountains. We know that the gun is a powerful symbol in this movie. But what about the ax and saw? I recall that in one camp-building scene, Jack is using an ax, while Ennis is using the saw. Do they just represent elements of their personalities??