Isonychia Beaver (Tutorial)

[letumgo]

Thanks for the pointers Mark. I though about the gills, but decided they were too much work for fishing flies. I think I could just pick out some of the dubbing along each side to simulate the gills. I like the idea of the medium dun hackle. Sounds like a nice material for a flymph version. I played around with another version (wiggle tail) this afternoon which used English Grouse wing coverlet feathers. I liked the look of the rich mottled brown hackle with the mahogany colored body.

Nice to be back at the vice...

[narcodog]

I use Emu for gills. I wrap it then trim short.

[letumgo]

Bob (narcodog) - Great idea! Wrapping Emu feathers are an elegant solution. I like it!

[willowhead]

Emu, prolly work just fine.....hate to waste it like that though........lol..........as aftershafts are just usually thrown away anyway..........i guess it's not a waste if, when your releasing the fish............nuff said. Aint tyed since last night.....better get one done.......

[tie2fish]

Great thread, with several good comments and observations. However, I think the flies pictured in letumgo's original post are extraordinary in their own right.

[William Anderson]

Fellas, again I have to raise the question about fly behavior and fishing methods. Isonychia's are quite unlike the typical mayfly hatch in that they move from rock to rock, crawl up out of the water, then hatch as duns. (gorgeous flies, btw, and the imitation fly is really nicely done).

How do wingless wets play into this scenario? I know there will be a stray that is dislodged on his migration or picked off the bottom gravel on his journey, but typically these are not headed to the surface in a typical ascent where a Leisenring lift is going to be the go to method.

Any thoughts?

w

[tie2fish]

Fellas, again I have to raise the question about fly behavior and fishing methods. Isonychia's are quite unlike the typical mayfly hatch in that they move from rock to rock, crawl up out of the water, then hatch as duns. (gorgeous flies, btw, and the imitation fly is really nicely done).

How do wingless wets play into this scenario? I know there will be a stray that is dislodged on his migration or picked off the bottom gravel on his journey, but typically these are not headed to the surface in a typical ascent where a Leisenring lift is going to be the go to method.

Any thoughts?

w

Drowned duns that got blown into the water perhaps? For what it's worth, I've also seen accounts offered by veteran outdoors folks (guides, etc.) about Isonychias actually popping up fully hatched from the surface of streams.

[narcodog]

William, that would be a great question that might be answered by the folks in the Catskill's. They are nuts for ISO's.

[William Anderson]

Bill, Mark mentioned that in high water conditions Iso's may shoot for the surface to hatch in the film, so that could be one way. A knocked down dun, that too. A wingless wet would certainly be the way to go for either of these conditions.

Bob, I love Iso's too. Along with Hendies, March Browns, Quill Gordons and Paralepts...they are my favorite. (smiley)

w

[letumgo]

William - I have remained silent on your question, in hopes that others more knowledgeable than I would chime in with their experience fishing the Isonychia Bicolor. Not having direct experience fishing this insect had lead me to do research in a few of of my fly fishing books.

Here is what I have learned so far:

Source 1 ("Fishbugs" by Thomas Ames / ISBN 0-88150-675-3 / Page 63) - Mayflies of the genus Isonychia hatch throuout the summer in many parts of the Northeast, with especially strong emergence periods in June and again in September on into October. It is one of the few mayflies that hatch out of the water, although it is perfectly capable of emergence in the conventional manner and will hatch on the water's surface in the early eason when the rivers are high. By late summer their split nymphal cases begin appearing by the dozens on the sides of stone flies a few inches above the water line. The early season adults are quite large and as dark as bittersweet chocolate, with creamy patchs in their slate-colored wings. By autumn they have diminished in size, their bodies are lithter, and wings more uniform. Isonychia have several peak hatch periods in a single season. Those that hatch directly from the water, or that are blown onto it after hatching seem to have as much difficulty with liftoff as an albatross. As they vigorously flap their wings, the whet the appetites of fish not previously disposed to feeding on the surface. A trout that charges impulsively up through the surface to chase a choise entree on the verge of escape is nature's equivalent of the Polaris missle. The species name comes from the distinct difference in shade between the dark ginger forelegs and the cream-colored second and third pair of legs. The tips of the insect's forelegs are also light, as if it were wearing gloves, and it holds them out like a carriage driver, for which it has earned the nickname leadwing coachman or, in the spinner stage, white-gloved howdy.

Source 2 ("Nymphs - Volume 1" by Ernest G. Schwiebert / ISBN 978-1-59228-499-3 / Pages 91, 271, 277-80, 281 - 284, 288, 472, 597 n2 / Selected passages only):

Mature adult Isonychia mayflies can be in the 15 to 18 millimeter lenghth range (mahogany bodies and chalky tails)

Eggsacks on the females will be dark olive (like tiny canned peas)

Isonychia bicolor nymphs are dark and have a pale median stripe on their thoracic carapaces. In some nymphs, the strip will not be continuous over the length of the back. The color of the strip ranges in color - dark ginger or ochreous case in some specimens.

Isonychia bicolor may differ in size, color, and silhouette depending on the fishery it is collected from, the pH of the stream, and degree of pollutants in the water (lesson - important to know what the local insect looks like to create a better immitation)

I (Schwiebert ) believe that the pale dorsal median stripes on our Isonychia nymps are triggering clues, and our trout forage on them throughout the season, beginning with the rapidly maturing nymphs of spring, to the much smaller, darker-bodied nymphs in October. The discrete axial strips of each species are important in designing effective imitations, because they will vary.

Schwiebert used the stripped center quill of a gray partridge feather to simulate the dorsal strip of the nymphs. He mentions that the stripped quills are delicate at their tips and much wider at their butts, in perfect simulation of the axial chalk-colored body stripes on the easter nymphs. The strips are thin and indistinct at their terminalia (tail), increasing in width until they are generous at the thorax. Mottled legs are imitated with several turns of dark brown-mottled partridge.

Mature Isonychia nymphs sometimes engage in surprising pulses of schooling behavior, and that during such migrations, large numbers gather in the rocky shallows before they hatch.

Isonychia nymphs are photophobic (lesson - fish in the early morning/late afternoon or in shaded areas) and become most active at marginal levels of light, and their mature nymphs are often schooling then. Schwiebert chose to fish the imitation at first light. He mentions fishing the runs slowly, in a series of parallel lines of drift, while working patiently upstream. He used imitations tyed on size 8 and 10 hooks (no make or model listed) and used unweighted patterns so he could work the shallow areas. The weight of the hook was enough to get the nymphs down and fishing in such shallow water. He mentions beginning fishing in the shelving depths offshore, casting a bit longer at first, and shortening each successive cast until fishing the shallow line of drift nearest the bank. Each parallel line of drift was approximately 2 feet apart. Watch closely for any pause in the drift and tighten the line.

Mature nymphs range between 9 and 18 mm in length, excluding their caudal filaments (tails). Axial stripes ranging from rusty ginger to chalky white are present on the dorsal surfaces of most Isonychia specimens, but these are not always contiguous, and their placement and length.

The gill plates (along the sides of the rear part of the nymph) are tightly closed while the Isonychia nymphs are swimming, to accentuate their smooth, fusilliform bodies. (lesson - I interpret this to mean that it is not important to include the gill plates in the imitation)

Mature nymphs prosper in the swiftest of the boulder-broken currents, and their restless agility and energy can be quite astonishing. THey are the true circus acrobats of the entire mayfly clan. Most seam to relish the tumbling spume, seaking sheltered refuge in narrow crevices and in the shadowy intersticies between stones inthe bottom cobble. High concentrations of dissolved oxygen are apparently critical to this genus.

The nymphs are unusually restless and active. Locomotion is accomplised with surprising vigor, in a kinetic series of restless little starts and bold spurts, and such swimming behavior suggest a somewhat erratic retrieve in fishing imitations of the Isonychia nymph.

(lesson - The nymphs are powerful swimmers and most likely to be found in areas with tumbling currents/heavy current/high oxygen levels. Fish the nymph with and active erratic start/stop retrieve. It will be important to use an open-loop knot to maximize the movement of the fly. An "S" shaped hook may be best representation of the nymph, especially if tyed in the round - soft hackle style.).

I am sure others can provide additional first hand information, but hopefully this is a start. This has been a fun post. Thanks for the probing question, William. You helped me learn something new about the actual insect.

Additional note about Schwiebert's book (volume 1) - Initially I found the size of the Nymph books intimidating, but have found that the text is very well written and enjoyable to read. I can see why these books have become such a classic reference work.