by Robert J. Matheson
Fly fishing a winter trout stream involves a binary approach : (1) reading the water, and (2) presenting the fly in a seductive manner. In this passage, we shall focus on the science of reading the water, which is perhaps the most challenging aspect of winter fly fishing. While the streamer methods fly fishers employ to catch winter trout are relatively straightforward and easily mastered, locating these weary ghosts during the winter months requires a departure from the standard means of analyzing a stream. Indeed, understanding the nature of a stream’s seasonal environment, and its effect on trout behavior is the cornerstone of fly fishing during the icy chill of winter.
To exemplify the relationship between seasonal environment and trout behavior, let’s examine the annual migration patterns of rainbow trout in the Cariboo-Chilcotin region of British Columbia. Rainbow trout enter the streams during spring to spawn, and often remain throughout the summer and autumn, gorging on hatching stoneflies, mayflies, and caddis. Although British Columbian streams possess abundant aquatic insects, the blue-ribbon systems such as the Babine, Stellako, Chilko, Quesnel, Stewart and Adams contain a secret ingredient - Pacific salmon. Pacific salmon, particularly sockeye (Oncorhynchus nerka), fuel the ecosystem, and their natural byproducts cause the extraordinary growth rate amongst the system’s rainbow trout population. These trout enjoy a high protein diet, which includes salmon eggs, alevin, fry, and flesh. After spending the gentle months in the streams, another migration occurs in early winter, whereby trout return to the lakes. Although the larger (lacustrine) trout spend the winter months in a stillwater environment, streams retain a population of resident (riverine) trout. In other words, British Columbian streams possess fewer fish during the winter months, but these resident trout are beautifully conditioned creatures, and are very responsive to a well presented streamer. Like elsewhere in North America, success on a winter trout stream in British Columbia requires skillfully reading the water, adapting your techniques to suit the environment.
As mentioned, rainbow trout in the Cariboo-Chilcotin region of British Columbia are prone to large-scale migration, but smaller-scale migrations occur throughout North America. This is particularly evident during the winter months. With the notable exception of spring creeks, a stream’s resident (riverine) trout will often inhabit different locations than in spring, summer, or autumn. As a generalization, the primary environmental stimulus causing trout relocation during the winter is water temperature. As water temperature drops stonefly, mayfly, and caddis hatches gradually degenerate. Consequently, trout abandon the prime feeding lanes, and seek the comfort of deeper pools. Like aquatic insects, trout physiology is also affected by water temperature. As water temperature drops a trout becomes increasingly lethargic, and its metabolism slows. A trout verges on hibernation, and consequently lacks an appetite. Instead of actively foraging, a trout conserves its energy during the winter months. Hence, a slowed metabolism accommodates the seasonal scarcity of hatching insects, but it also necessitates that less energy should be spent fighting heavy currents, and therefore winter trout seek pools and off-current lies.
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