Use Big Stonefly Nymphs During Winter

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Use Big Stonefly Nymphs During Winter

By: Mark Bachmann

Picture, A tiny winter stonefly adult crawls onto my fisnger.

A tiny adult winter stonefly crawls on my finger during a heavy winter rain.

On many river in the west there is a regular procession of stonefly hatches during the winter, but most of these insects are tiny, and most hatches are too sparse to draw trout to the surface. With a few exceptions the stoneflies that hatch in January and early February are size #18-#20. Then through late February and March slightly larger species  (#14-#10) crawl out. Some of these winter hatches trigger reliable dry fly fishing, as well as nymph fishing during migrations just prior to emergence. There are also trout feeding during behavioral drift cycles of these same insects. But, the nymphs of the main spring super-hatch (Salmonflies) gives more rewards in caloric gain than the winter hatches. The most renowned Salmonfly hatch in Oregon occurs on the lower 100-miles of the Deschutes River, with scattered populations throughout the entire Deschutes basin. Salmonflies range from Alaska to northern Mexico, and from the Pacific coast and east as far as Eastern Montana, Wyoming, Colorado and New Mexico. Streams that run north or south have dramatically heavier populations than streams that run east or west.

Picture showing three ages of salmonfly nymphs from the sam stream at the same time.

Three generations of Pteranarcy califorica nymphs are different sizes at the same time.

What many anglers don't realize is that larger stoneflies such as salmon flies Pteranarcy califorica can have three or even four-year life cycles. That means they are available as trout food year around in several different sizes at the same time. It is not unreasonable to assume that during any winter day in any river, a wide variety of salmonfly nymphs sizes might all be available to trout. Pteronarcys nymphs grow through many instars (12 - 20 of them). At each instar they attain a larger size. The length of the life cycle is 3 to 4 years depending on elevation and degree days (water, temperature and air) (Baumann et al. 1977).

picture of a fat trout caught from Oregon's Deschutes River during winter.

Trout are fat during the winter.

Most of the time these Salmonfly nymphs are hidden under debris of the stream bed and are only occasionally available to feeding trout. But they are nearly always available during behavioral and catastrophic drift cycles. Behavioral drift cycles can occur nearly every day. Nearly all aquatic stages of insects have behavioral drift cycles to redistribute populations into areas where more food and space is available. Catastrophic drifts are caused be natural or man-made catastrophes such as fluctuations in water flow or an angler wading in a stream. The results are alterations in the stream-bed where bottom structures are dislodged, and insects are turned loose in the currents. Behavioral drift cycles usually happen during low light conditions, especially early mornings. Catastrophic drifts are more random, but winter flows have a lot of water fluctuations. Trout are capitalists that will feed on any aquatic insects that are exposed, especially if they are exposed in large numbers. Pteronarcys nymphs have behavioral drifts nearly every morning during the winter months. It pays to have a kick-screen to sample the river bottom and see which sizes of nymphs are liable to be available in the area that you plan to fish. Also have a selection of flies to match the different sizes of nymphs that you find.

Picture showing an angler fishing an uncrowded river during winter.

Rivers are usually deserted in winter

Fly List:

Bead Head Black Rubber Leg Stone 

Improved Rubber Leg Stone Golden 

Tungsten Poxyback Stone 

Bead Head Rubber Leg Hares Ear 

Bead Head Prince Nymph

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