Population Survey Shows Record Number of Trout in the Big Lost River

The summer of 2022 marked nearly 40 years of basin-wide monitoring of trout and mountain whitefish populations in the Big Lost River basin.

The first round of monitoring these populations began in 1986, and we have been continuing this work at the same sites into 2022. A lot has changed in addition to the numbers of fish that we encounter since the first year of monitoring. Those changes include water usage, diversions, fish passage, snow pack and precipitation, stocking rates, species introductions, harvest regulations, fish salvage, field crews and fish sampling equipment.

As a result of these changes, we also observe changes in fish distribution throughout the basin, and the number of fish that we count at our 30 standardized sampling locations. Some of the more recent changes that we have made to improve fishing include stocking Yellowstone cutthroat trout and translocating South Fork Snake River rainbow trout into the Big Lost River and its tributaries upstream of Mackay Reservoir.

In addition, with the help of the United States Forest Service we have begun saving fish from being stranded (or entrained) in irrigation canals and diversions by electrofishing those canals and relocating fish back into the Big Lost River and its tributary streams, also known as fish salvaging. More than 13,000 mountain whitefish have been salvaged as a result of these efforts. These actions have made fishing better by boosting the number of fish in streams and by preserving and perpetuating the native mountain whitefish population.

To be more specific about the number of fish that we surveyed and the health of the fish populations in the Big Lost River basin, we counted more fish in 2022 than in 2017 (the last basin-wide survey) at 72% of locations, with increases in the number of fish up to 162%. One trend that we noticed is an increase in trout and mountain whitefish abundance in the main stem of the Big Lost River upstream of Mackay Reservoir.

Mountain whitefish abundance is at a level not seen since the last decade, and trout abundance is the highest estimate on record. The figure below depicts the number of trout per mile in the upper main stem of the Big Lost River from 2012-2022.

big lost river basin wide population monitoring

We believe that through fish salvaging and changing stocking practices we have been able to boost the number of fish in this fishery and improve fishing for anglers. We will continue practicing fish salvaging both upstream and downstream of Mackay Reservoir, stocking Yellowstone cutthroat trout and translocating South Fork River rainbow trout to the upper Big Lost River basin to make fishing better for Idaho anglers.

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