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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Lateral view of a Onocosmoecus (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.
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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Bellevue, WA

Posts: 2758
Troutnut on Oct 4, 2006October 4th, 2006, 3:51 pm EDT
For those who didn't see the link in the "Recent updates" column, check out this neat photo sequence of an Isonychia bicolor nymph emerging on a rock in Esopus Creek in the Catskills.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
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"Bear Swamp," PA

Posts: 1681
GONZO on Oct 6, 2006October 6th, 2006, 12:37 pm EDT
These are truly extraordinary shots, Jason! I'm struck by a couple of things:

The crossveins and milky areas of the dun's wing really stand out. Did you play with the contrast, or is this enhancement-free?

Your comment about the precarious position of the emerging dun brings up something I've never considered. I know you're probably more familiar with those suicidal Midwestern Isonychia that like to emerge in open water, but it's not unusual to see the Eastern variety lined up on nearly vertical rock faces. It does make me wonder, though, if they select emergence sites for the degree of grip they provide. Perhaps this is why one rock may have a dozen shucks while a nearby rock has none. Just an idle thought, but one I've never entertained until I saw this sequence. I wonder if stoneflies might do the same?

I'm also reminded that I usually fished a dark, unstriped nymph imitation in the "old Esopus". On the Brodheads, many (but not all) of the Isonychia are distinctly striped. Did you notice any striped shucks on this day or were they all plain?

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Bellevue, WA

Posts: 2758
Troutnut on Oct 7, 2006October 7th, 2006, 4:56 pm EDT
The shucks I noticed on the Esopus and Schoharie that day were all plain. I've collected and photographed really heavily striped Isonychia nymphs on the Beaverkill. The early summer flies are, I think, a distinctly different breeding population from the fall ones, and I wouldn't be surprised if some rivers have both striped and unstriped Isos at different times. And half-striped. It's quite a variable trait.

Interesting question about the selection of emergence rocks. I really noticed that on the Schoharie. If you check out the Isonychia page you'll see a couple streamside photos from there with lots of shucks on a few rocks in one spot, and there were relatively few elsewhere.

It seems to me that they can be concentrated in very specific spots, but often they're on two or three close-together rocks rather than one particular rock. And lots of the unselected rocks seem to be of the same type. This makes me think they're responding to other location factors like current and sunlight instead.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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