The 5 Most Popular Spring Bugs Trout are Feeding on in Wyoming Stillwater Lakes

Ever wonder what fish in local stillwater lakes are eating in the spring?  The study we helped with had some surprising results.

Hogan and Luce Reservoirs Study

The Wyoming Game and Fish Department sampled fish populations of both reservoirs using gill nets in 2020 for various fishery management reasons, with East Yellowstone Trout Unlimited chapter members and guests analyzing the stomach contents of all the fish collected.  Four years later (2024) the trophy fish in Luce Reservoir now average 20 inches according to the Game and Fish Department.  

Chironomid pupae were the main food source in both reservoirs, this tends to be true in the spring for other local “mud” bottom type water bodies such as East Newton Lake.  This study provided excellent intel for those looking to fly fish in Western Wyoming in the late spring on what to tie before heading out to fish.

May 27, 2020 Hogan Reservoir Study Results

60+ fish sampled, nets placed yesterday, removed 8-9 am today

Yellowstone and Snake River Cutthroat Trout made up the sampled population, 16 inches in length was the largest fish, most were in the 10-14 inch range

No hatches were in progress, black chironomids flying around by total biomass (visual estimate of stomach contents from all fish sampled).  Most fish had very full stomachs.

Analysis on stomach contents revealed the following:

95% chironomid pupae, size 10-12, dark olive/black

The remaining 5% consisted of:

1 small scud,  orange in color

Couple of sedge caddis in cases, green abdomen color, 1 inch long with cases made of bulrush/wood pieces

Couple of dragon fly nymphs

Few damsel fly nymphs (reddish bodies)

Few small snails

Some zooplankton

No minnows, callibaetis mayfly nymphs or leeches

​May 28, 2020  Luce Reservoir Study Results

50+ fish sampled, nets placed yesterday midday, removed 9-10 am today

Rainbow Trout made up the sampled population, the longest fish (shown in the above photo) was 19 inches in length, but was 8 years old according to Joe Skorupski (G&F biologist) based on the fin clip.  About 25% of the total number sampled appeared to be in this old age category.  These fish had a more slender body with a bigger head in proportion to the rest of the body. The full stomachs showed these fish were eating as much as the younger fish, with little or no additional body growth expected according to Joe.

Numerous age classes were present, with many 3-4 year old fish in the 16-18 inch length range weighing 3-3.5 lbs each.  These fish appeared very healthy, having big bodies and smaller heads as shown in the photograph below.  Hopefully the remaining fish of this size will grow to the desired 20+ inches in length over the next couple of years.

Trout had full stomachs, only a couple had empty stomachs.

Analysis on stomach contents revealed the following, by total biomass (visual estimate):

80% Chironomid pupae sizes 10-12, mostly 10’s, dark olive/black with yellow head.  Overall the pupae were a little larger in size compared to those in Hogan.  

5% scuds, orange in color, small in size (18-20),  

5% snails, small in size (16)

5% traveling sedge caddis larvae in cases of bulrush/wood pieces, some 1 inch+ long, abdomen green in color, none of the tan/yellow abdomen color  

5% damsel fly nymphs (a few adults flying around), some nymphs starting to migrate to shore.  These were larger in size than the ones we saw at Hogan, and dark olive in color.

no zooplankton, minnows, callibaetis mayfly nymphs or leeches​

If you have any fishing intel from any of the lakes here this spring, please head over to our Facebook Page and share your findings on what flies worked for you.  We would love to see photos as well. Please reference our Events Page for educational and volunteer opportunities for all ages.

Article by Duane Feick, East Yellowstone Trout Unlimited Member, whose next article will be taking a closer look at the insects in this study.