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  1. #1
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    Puzzling phenomenon!!! An "almost hatch"

    Yesterday on the Namekagon River in northern Wisconsin I noticed a really strange behavior among some Ephemerella mayfly nymphs (the genus that includes the Hendricksons and the Sulfurs). They were swimming by the hundreds up off the bottom and wiggling all the way to the surface as if they were going to hatch, but they didn't. They just wiggled around in the water column and, I assume, made their way back to the bottom.

    This was happening in the middle of the day, with the water temp in the 30s. It's too cold for any Ephemerella species I know about to be hatching, although one person e-mailed me that he caught a thick hatch of size 12 BWOs on this river a few days ago. I'm baffled by that--I haven't found any Drunella nymphs in my extensive sampling of this river, and as far as I know they're the only mayflies around that size which are known as BWOs. It may be related to this weird phenomenon I saw yesterday, but I don't know.

    It's also possible that this was the normal "invertebrate drift" phenomenon, but that's supposed to peak around sunrise and sunset. This behavior was only taking place during the warmest part of the day, and it seemed to intensify when the sun came out from behind the clouds every once in a while.

    So, I'm baffled. I'm also not sure what species of nymphs were doing this weird "almost hatch" stuff--I collected two by reaching down and grabbing them with my fingers just under the surface. They most closely resemble Hendricksons, Ephemerella subvaria, but they're more of a ruddy brown than the olive color of E. subvaria and the abdominal tubercles aren't quite black. Below are pictures of two of the nymphs I scooped up:

    Does anyone know for sure what species these are, and has anyone seen nymphs behaving like this before? I've never read about it, and it seems like the kind of activity that would really get the big trout going. I'd love to understand what was going on and why.


  2. #2
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    No clue on what species, but pretty sure from what I have read, this is the " Drift Phenom" re:the Paradox is, that if the hatched insects fly and lay eggs down stream, that particular species will eventually dissapear from that stretch of water. But they Don't!
    They actually move back up stream and start all over again. Yea!


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    It probably didn't make a difference. Those things must have scared the hell out of the fish as they were drifting by. Look at the size of 'em.


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    I have a question. What are you using to see this kind of activity while streamside? Don't tell me you are in thirty degree water in a snorkeling outfit.


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    I have a question. What are you using to see this kind of activity while streamside? Don't tell me you are in thirty degree water in a snorkeling outfit.
    Hehe, I don't even like going in 70 degree water in a snorkeling outfit.

    I'm just standing there in waders looking down into the water. It's amazing what you can see doing that if you look closely and focus on the little particles drifting by... sometimes lots of them are alive! Same goes for staring at the bottom... you can see a lot of these guys crawling around on the bottom in the shallows while just kneeling there staring down at the rocks, especially in a particularly fertile stream.


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    Looks like a typical Hendrickson to me. How long is it in mm?

    Pictures taken before/after/during fly fishing:
    http://dcabarle.smugmug.com/Sports/F...79119552_XXeHe

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    I'm with Dennis. I think it's a subvaria too. My second guess would be another emphemerella.

    Allan

    Allan

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    Subvaria species have at lest 6 sub-species that are closely related and do vary in Color,so that might answer you color question.However its not the Genera or species that I question its what caused this acivity with such cold water temps?

    Invertabrae drift as you stated does occur at sunrise and sundown but there are theories that -"over crowding" can cause this behavoir.

    Was it warmer previous to this?
    What where the temps preceeding this activity?
    How cold was the fall and winter?

    The reason I ask is that it may be that enough thermal units or degree days accumalated and this species is just ready to hatch.

    I guess the wing pads where very dark?(I cant tell from photo)

    Another theory is instars; although not documented as far as I know can possibly cause this activity.It's possible that the latter stages of "moulting" may cause hyperactivity.


    Over the years I have always been intrigued by phenomenoms of nature regarding Fish,Deer,and aquatic insects.This is a question that does not fall into the "norm" category and I think needs to be thought out from outside the box.


    Let me know what you find out and what you think.Thanks.


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