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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Another fun day running around the West, and my first goofy attempt at Euro nymphing

Another fun day running around the West, and my first goofy attempt at Euro nymphing

By Troutnut on August 1st, 2020
I fished from 7:30 am to 2:00 pm in the area I had hoped to fish the night before, if I hadn't see too many vehicles. I was the first one there, but a couple other guys arrived soon. I walked pretty far from the parking area, and I started fishing. upstream. I worked upstream with dries and nymphs, seeing no early action, but spooking a few good fish. Finally I saw one before it saw me, and I successfully targeted it with a perdigon-like nymph ("Spanish Bullet") under an indicator. That was the beginning of a great morning chasing big cutthroat.

My uncanny success with a nymph made for tight-line or Euro nymphing, despite using it on my usual 5-weight with a typical indicator, motivated me to finally give my new Euro nymphing rod and reel a try at my evening stop, the Big Lost River near Mackay, Idaho. I left my normal rod in the car and walked a good distance down to the river, committing to flailing around with the new technique and seeing what happens. Some good fish were rising, and nothing was touching my nymphs. I tied on a dry, flailed it around on the end of a very long leader of lightweight monofilament, and somehow managed to fool a 15" rainbow. Interesting way to inaugurate the new rod!

Photos by Troutnut from Mystery Creek #237 and the Big Lost River in Montana and Idaho

I was trying out my dedicated Euro nymphing rig, having left my regular rods half a mile back in the car. This fish and others were rising to some sparse evening hatch, and nothing would even take a passing interest in my nymphs. So I put on a more appropriate dry fly and flopped it out in ridiculous form with my nymphing line/leader. This was the first nice fish on the rod (16" rainbow) and great fun, but was it cheating to break in the new nymphing rod with a dry fly?
The Big Lost River in Idaho
The Big Lost River in Idaho
The Big Lost River in Idaho
Road leading through the sagebrush BLM land down toward the public access on the Big Lost River.

From the Big Lost River in Idaho
Pronghorn antelope overlooking the river valley.

From Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
At 21" this was the big fish of the day.
Mystery Creek # 237 in Montana
Mystery Creek # 237 in Montana
Big sky country!

From Mystery Creek # 237 in Montana

Closeup insects by Troutnut from the East Fork Big Lost River in Idaho

Lateral view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
This "specimen" is actually two different duns, one missing the middle front and back left legs, the other missing the terminal filament i.e. middle tail. I added them together by accident, but since they're the same species, stage, and gender, I might as well leave them together.

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