According to research from David Stagliano of the Montana Natural Heritage Program, salmonfly numbers across Montana are in decline due to warming river temperatures. Previously, it was assumed that salmonflies were more dependent on dissolved oxygen content than water temperature, but Stagliano’s research proves otherwise. It’s fascinating reading, especially if you’re fond of fishing salmonflies in Montana’s famous rivers.
All the anecdotal evidence that hatches aren’t what they once were also has some merit, according to the research. As rivers have warmed across Montana, salmonfly numbers have followed a similar decline. In some stretches of the Smith River, for example, one study Stagliano cites in his research asserts that salmonflies have completely disappeared.
You can find all the research here.