2012: A Forecast

Posted by & filed under HARROP'S FORKED TONGUES.

Throughout my entire memory I have relied on a fixed set of indicators when attempting to predict what lies ahead in a new year on the Henry’s Fork. Reflection on the previous season is the general starting point.

A season of weak hatches and low trout populations are seldom followed by substantial improvement in the following year. Conversely, a season yielding sustained dry fly opportunity to solid numbers of rising trout can be altered in the following year by the effects of catastrophic weather conditions or man caused disaster such as the great siltation event of about twenty years ago. Severe icing caused by excessively cold temperatures can devastate the habitat and numbers of trout as well as the aquatic insects which they depend upon for their existence. Inadequate water flows are known to suppress trout numbers, and such conditions are also not ideal for insect survival.

Most who fished the Henry’s Fork in 2011 would agree that the quality of experience from Box Canyon to Riverside was the best in nearly a decade. This stretch includes the fly only water of Harriman State Park where disappointment was often the result in the first few years of the new century. This improvement has been the gradual result of beneficial winter flows negotiated by the Henry’s Fork Foundation over the past four years and the absence of serious icing problems during the same period. The recent reconnection to the Buffalo River is also believed to be a contributor to improved trout numbers, although this has not been officially confirmed.

Veteran of the Fork have noted a resurgence of aquatic vegetation in areas that were over harvested by waterfowl during periods of inadequate water flows. Once considered empty water, these areas have returned to producing the customary habitat and insect activity that must be present in order to become occupied by trout.

While trout in the 18 inch range and larger were certainly present, the number of young adults that will soon enter that size category were in greater than usual abundance in the year just passed. These 14-16 inch fish that have been in the system for three years are a lively testament to a healthy fishery that continues to benefit from the cooperative efforts of local water and state fishery managers along with the dedicated staff of HFF.

An abundance of water carried over from the 2011 irrigation season has allowed flows from Island Park Reservoir to average about 500 cfs through the cold months most critical to trout survival. This, combined with a mild winter in terms of temperature and duration, has set the stage for the likely continuation of trout prosperity in the current year. Also factoring into this sense of optimism is a new indicator that has been available for only slightly more than one year.

With fishing above Harriman State Park now open year round locals have thoroughly tested the productivity of the Box Canyon and Last Chance stretches throughout the winter. While adequate in terms of providing stream flow, the lower snow pack of the past winter allowed relatively easy access to the newly opened water, and the fishing results were more than simply encouraging. This especially applied to Last Chance Run when nearly every day of reasonable air temperature would deliver good numbers of midges, Baetis, and rising trout. Vigorous spawning activity was easily observed beginning in March with size and numbers of trout being equally impressive.

An early end to winter found Island Park Reservoir filled to capacity by mid- April, and spring runoff was well underway by the beginning of May. Though spring conditions can always change, a repeat of last year’s excessively high water through late June seems unlikely.

Anglers and other river users watched rather anxiously as the Ashton Reservoir was drained for critical repairs on the Dam late last summer. Higher than usual flows for that time of year and a moderate release of sediment caused unavoidable disruption to fishing from late August through October. Though significant damage to the fishery below Ashton Dam was not identified, trout and insect activity were not typical through late fall, winter, and early spring. I am assuming that colder water temperatures due to water flowing from the surface of the reservoir was influential in suppressing midge and Baetis hatches during that period, although nymph and streamer fishing was quite productive. This speculation is supported by a change that occurred in mid-April when unusually warm temperatures caused the lower river to spring to life. By early May extremely strong hatches of midges, Baetis, March Browns, and caddis began to appear as weather conditions returned to the seasonal norm.

A second and final drawdown of Ashton Reservoir is planned for around mid-May which will allow for the final phase of dam repair to be completed. Authorities expect the drawdown to be completed in advance of early June when fishing on this stretch of water is normally at its best. Serious sediment release is not anticipated during that period. Of course, this event will be closely monitored by HFF personnel as has been the case throughout the project. If all goes according to plan, fishing between Ashton Dam and Fun Farm should be fine.

While official verification has not been established, it is reasonable to assume that the river could be the recipient of trout escaping from the reservoir during the drawdown of 2011 and 2012. The transfer of several thousand stranded trout from a pool below the dam to the river downstream does lead one to speculate, however. This rescue was conducted by staff from Idaho Department of Fish and Game last winter, and their efforts are appreciated.

Allowing further deterioration of Ashton Dam was not an option and the managers of the rebuilding project should be commended for the consideration they have given to the fishery downstream. Thanks are also due to the Henry’s Fork Foundation and Idaho Fish and Game Department for their determination in protecting this special stretch of the Henry’s Fork.

Regional Fisheries Biologists will complete population sampling on the lower and upper river by mid-May. It normally takes a few weeks to crunch the numbers but results should be available by early June.

3 Comments

  1. Claudio Tagini

    Thank you again for the precious information and insights

  2. Stephen Johnson

    Thanks for the insightful comments.

  3. Steve Born

    Rene - thanks for a great report! As usual, filled with insights that only an "old-timer" expert can have. Looking forward to seeing you on the river soon.

Leave a Comment



Note: All comments must be approved by the post author.