Observing the Henry’s Fork through the winter of 2009/2010 has been vastly different from the previous two years. Comparatively modest snowfall and mild temperatures provided unusual comfort to all river dependent creatures both aquatic and otherwise.
Wintering whitetail deer were not forced to concentrate in the river corridor for forage as in years past, and I have yet to see a single casualty of the cold season. Without severe icing influencing their survival, Trumpeter Swans and other waterfowl were free to access the entire length of the river thereby avoiding crowding and over harvesting of aquatic vegetation. Vulnerable mammals like muskrat also benefit from less severe conditions, and spring numbers of these gentle creatures attest to an easier life during the past winter.
Lower snow levels have permitted the observation of many spawning areas that would otherwise be difficult to reach in typical early spring conditions. Reproductive activity in these key locations is perhaps the best indicator of trout populations separate from actually fishing. Impressive is the best word to describe the numbers and individual size of spawning rainbows observed from early March through the end of April. The volume of predatory activity from Bald Eagle, Osprey, Loons, and river Otter might be troubling to some but it takes a strong fishery to attract and support such intense interest. Therefore, it seems logical to consider these wild consumers as positive indicators of a very healthy population of trout.
Mild weather aided by easier access to the water enabled anglers to get an earlier start on waters open to year round fishing on the ‘Fork. Early March found trout rising consistently to abundant hatches of midges and baetis, and this trend continued for more than six weeks. Clearly evident was a higher percentage of brown trout that were coming to a dry fly which indicates a strengthening of this relatively new resident of the lower Henry’s Fork.
Caddis and March Brown mayflies began to appear almost simultaneously during the third week of April bringing with them a nearly unbearable distraction for the heavily burdened fly tyer only thirty days out from the beginning of the general fishing season. Cool temperatures with weekly precipitation are perfect weather ingredients for heavy hatches and rising trout, and this has been the pattern since late March. Also positive in this trend is a strong contribution in the high country to a weaker than usual snow pack.
Key in the outlook for 2010 is winter flows from Island Park Reservoir that exceed anything we have seen on the Henry’s Fork since the late 1990’s. With flows running from 350 to 400 cfs during the coldest months of December, January, and February, a much higher percentage of young trout will survive than in years when winter flows were considerably lower. Large numbers of small trout now concentrated along the edges of the river confirm a continuing trend of improved winter survival that can be largely attributed to the efforts of the Henry’s Fork Foundation. Working in close cooperation with irrigation officials who control the release of water from the Island Park Reservoir, HFF personnel have succeeded in gaining unprecedented consideration for trout in the management of winter flows on the Henry’s Fork.
Aquatic insects that share environmental needs similar to trout are also benefiting from better wintering conditions. Strong hatches and an abundance of rising trout have persisted through the early season and I see little reason to expect this to change as the season progresses.
Concerns for a lower than average snow pack can be alleviated to a considerable extent by a large carryover in Island Park Reservoir that now approaches 100% of capacity. Cool temperatures and above normal precipitation beginning in late March and continuing through April have delayed spring snow melt and irrigation demand thereby improving the water outlook as well. More rain and perhaps even snow dominate the forecast as April draws to a close, and this is bad news only to golfers.
Winter in the adjoining states of Montana and Wyoming has been similar to what has been experienced in Idaho. Anglers who plan to visit the Yellowstone region should not expect to find rivers swollen by heavy runoff in late May and June as has been the case in the past two years, although this could change with continued cool temperatures and abundant precipitation.
2009 on the Henry’s Fork was the best in recent memory with abundant hatches and trout of impressive size and numbers. Based upon customary indicators, it is reasonable to expect fishing in 2010 to equal or even exceed what most fly fishers experienced last year.