Evaluation of salmonflies in Montana's rivers : are statewide populations really declining? /

Abstract

The fabled salmonfly hatch on Montana's rivers can be an exciting and frustrating angling experience all rolled into one; exciting because huge trout can be coaxed to the surface by giant dry flies (size 4 or 6's) and frustrating because, oftentimes, this sporadic hatch coincides with spring runoff , murky water and less than ideal fishing conditions. To add to the exasperation, a thousand like-minded fishermen from all parts of Montana and adjacent states are invading your favorite stretch of river. Successfully "hitting" the salmonfly hatch is both an art and a science; mixed with a lot of luck. Arrive too early and the fish are still focused on underwater nymphs; too late and the trout have stuffed themselves silly, already seen a thousand artificial stoneflies float overhead and are now extra selective when deciding to eat one more "floating steak", as I've heard these insects referred. Last season's tremendous salmonfly hatch on the Big Hole River surprised a lot of anglers in its extent and duration. "Many of our customers experienced their best success fishing the hatch in decades." said Roger Oettli of Great Divide Outfitters. Before this past spring's great hatch on the Big Hole, anecdotal and perhaps some scientific evidence exists that have lead many fishermen and fishing guides to declare that the salmonfly hatches occurring recently: "Are not what they used to be"and "in decline". Mark Canfield, a former fishing guide on the Smith and Missouri Rivers, as well as having a background in aquatic biology, reported to Background: Montana's rivers provide habitat for three salmonfly species: the famous, giant salmonfly (Pteronarcys californica), the lesser known American salmonfly (Pteronarcys dorsata) and the smaller, least salmonfly (Pteronarcella badia) which can tolerate warmer water temperatures than the other two species. Ideal water temperature for P. californica development is 55.4-58º F, while P. badia is a presumably a few degrees warmer. These salmonfly species occur in many rivers across the state and cooccur in some (Figures 1 & 2, Appendix A & B), but only in a few rivers are they abundant enough to present anglers a worthwhile hatch. All three species have conservation ranks of G5 (NatureServe 2010), which means they are globally common and are yet to be ranked at the state level. Gaufin et al. (1972) cite the Missouri River in Cascade Co. as Montana's only distribution of the American salmonfly, but more recent studies report this species present in the lower Smith River as well (Bollman 2000). Salmonflies are easy to identify mostly by their tremendous size; these stoneflies (Order Plecoptera: Family Pteronarcyidae) often measure nearly three inches in length. As adults, they have a bright orange or red band behind the head and the underside of abdomen with broad wings containing dark veins. Salmonfly nymphs live on the bottom, crawling around on cobbles and feeding on large organic materials (leaves) in the spaces between rocks for three to sometimes four years. They require welloxygenate...