What’s the harvest rate for trout populations in Idaho alpine lakes?

This past winter was very good for snowpack in Idaho mountains, which is great news for trout anglers. High river flows in the spring clean the gravel that trout use for spawning and revitalize important stream habitat components such as undercut banks and large wood pieces. High flows re-fill impoundments like Blackfoot Reservoir and Magic Reservoir which, during drought years, can experience very low water levels that ruin trout fisheries until the next big water year returns. While heavy mountain snowpack is good for trout populations, it does shorten the fishing season in alpine lakes. This year, such fisheries may not be accessible until mid-June or later, but once the ice melts and the snow clears, alpine lakes can provide a scenic and memorable fishing experience. 

The Idaho Department of Fish and Game regularly stocks hundreds of alpine lakes, usually with trout fry that are dropped from an airplane. Many lakes also now have self-sustaining, wild trout populations, so the stocked fish merely supplement the natural production already occurring in some lakes. Because these waters are pretty remote, daily bag limits of six trout (of any size) apply to nearly all alpine lakes, and angling effort has been presumed to be relatively low. However, because these lakes are difficult to study, due to their remoteness, estimates of the number of trout harvested have actually never been produced here, or anywhere else for that matter. Without such information, fisheries managers have just assumed that angler harvest is not negatively affecting the size of fish available to anglers, or the catch rates at these waters. 

To test this assumption, Department staff tagged trout in alpine lakes, as part of the Tag-You’re-It Program. To date, almost 1,200 fish have been tagged in 113 different alpine lakes scattered across the state. Anglers caught tagged fish from as short as 1 day to as many as 1,465 days after they were originally tagged! On an annual basis, anglers catch and release slightly more fish (9.2% of the population) than they harvest (7.3%). Anglers have reported catching tagged fish in lakes nearly 20 miles away from the nearest trailhead, which shows just how far some anglers are willing to hike to catch trout in the high country.

These results have confirmed that angler harvest in Idaho alpine lakes is low enough that it has little impact on fish size or the catch rates anglers will likely experience. The reason for this is because total annual mortality rates for trout in alpine lakes are about 50%, and when harvest only makes up a small fraction of that number, then it doesn’t really have much impact on the population as a whole. Instead, most fish die of natural causes. The fact that anglers are more likely to release the fish they catch rather than harvest fish is probably the result of the widespread voluntary catch-and-release philosophy among trout anglers, which has become more commonplace over the last 30+ years. 

Based on this information, there is little reason to change fishing seasons and limits in alpine lakes, and anglers should feel comfortable harvesting fish if they so choose. Fish and Game staff will continue to tag trout as part of the annual population monitoring in these lakes to get more information from more lakes on trout harvest rates in the backcountry. We also appreciate the willingness of anglers to remove and report the tags they encounter in fish around the state – it provides biologists with incredibly valuable information to help manage Idaho’s fisheries.