Breaking the Ice
Reducing Elk Mortality at Lucky Peak Reservoir

By Jerry Deal, Habitat Manager
Idaho Department of Fish and Game
Southwest Region

Migrating elk should have no problem crossing Mores Creek this winter as they move to lower country a few miles east of Idaho's capitol city.

Even the casual observer of wildlife-related events knows about the elk that went through the ice at Lucky Peak Reservoir last winter. An unusual set of circumstances came together last January, resulting in the loss of 90 elk as they attempted to cross the ice-covered reservoir at Mores Creek.

Maintenance work on Arrowrock Dam during 2003 and early 2004 necessitated that Arrowrock Reservoir be drained almost completely. The water that would otherwise have been stored in Arrowrock was pushed through to Lucky Peak Reservoir. When all was said and done, the water level in Lucky Peak was 40 feet higher than the 25-year average for the reservoir. The higher-than-normal water level back-flooded the Mores Creek arm of the reservoir above the Highway 21 bridge, an area that is normally only a creek during winter months. As ice formed on the surface of the deep water, and snow accumulated on the ice, the narrow reach of reservoir seemed an optimum place to cross, at least to migrating elk. While many crossed without incident, several small groups of elk went through the ice and could not escape.

One other major factor last winter was the change in elk movements. Wildlife managers were surprised to observe large numbers of elk moving down the Middle Fork of the Boise River onto the Boise Front (although in recent years increasing numbers of elk have spent the winter in the Spring Shores area). In a normal winter, thousands of mule deer and very few elk spend the winter on the Boise Front. Last year, more than 500 elk moved onto the front, mostly after successfully crossing reservoir ice.

Mule deer frequently travel on reservoir ice, and most do so successfully. Elk, however, are much heavier animals, and travel in larger groups than is typical of deer. When startled, elk tend to close ranks and form tight clusters. When standing on an ice-covered reservoir, this behavior is a formula for disaster.

Once the initial problem of elk falling through the ice was observed last January, several actions were taken to prevent further elk losses. Excellent support was provided by volunteers and Fish and Game reservists and employees to haze the elk away from the reservoir on a 24-hours basis. Senator Brad Little allowed Fish and Game to place hay on his land to lure migrating elk to another location near a safer Mores Creek crossing point. In an attempt to provide an ice-free corridor of water, a bubbler system was installed across the Mores Creek Arm, in hopes that the elk would opt to swim the channel rather than walk the ice. Unfortunately, this option proved ineffective. Building a temporary fence to redirect elk movements was also considered but determined to be logistically impractical. Fortunately, the combined efforts proved very successful; no more elk were lost through the ice.

While these temporary fixes proved relatively effective last year, it was obvious that a long-term solution was needed to avoid a repeat of last year's events. Through a cooperative venture with the U.S. Army Corps of Engineers (which manages the dams), the U.S. Bureau of Reclamation (which manages the reservoir water), and Idaho Fish and Game (which manages the elk), Lucky Peak Reservoir will be held at a level that will allow the Mores Creek arm of the reservoir to be just that — a creek. Elk determined to cross the reservoir at that location will only risk getting their hooves wet; otherwise, they will cross dry land to reach the other side of the canyon. Of course, what the elk will actually choose to do is not always predictable (ask any elk hunter), but Fish and Game will monitor elk movements in the area and attempt to stay ahead of any recognized problems.

And now for a bit of perspective. While last year's loss of elk through the ice was tragic, motorists across Idaho kill far more elk and deer each and every winter. As winter approaches, and big game animals begin their migration to lower elevation wintering areas along Highway 21 and elsewhere across Idaho, motorists are reminded to stay alert, and drive the speed limit (or less) through these wintering areas to reduce the risk of big game animal/vehicle collisions. If we all do our part, many more big game animals will live to see another Idaho summer.

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