"rw" wrote in message
m...
riverman wrote:

Did you, or have you ever noticed what I mentioned about the 'diagonal
rising zone' of the nymphs on a stream? I always sort of figured that
the
nymphs would be rising in a sort of inverted snowstorm: all going
upwards at
all depths of the water column. What I saw was quite different, up by
the
source eddy, there were none near the surface, and I suppose a dozen
meters
downstream, there were none at the bottom.

I'm not entirely sure what you mean by "diagonal rising zone." I've
never seen nymphs rising to the surface. Maybe your eyesight is better
than mine.

One thing I have noticed, and particularly in this green drake hatch, is
that the bugs weren't emerging all over the river. They appeared in a
certain type of current -- fast and deep. The river is still pretty
high, but clear. These were not places you'd normally expect to find
trout holding. The only reason they were there was to feed actively, and
they didn't have much time to nail the big duns.

One cool thing is that you could tell where the mayflies were emerging
by watching birds. Robin, blackbirds, and western tanagers would swoop
out from the back to nab duns in the air, and tree swallows would pick
them off the surface.

You can use the bird situation to model the 'diagonal rising zone'. If the
emergers were coming up at a certain spot in the river, and there was as
light breeze (say, blowing southwards), then the birds would not all be
congregating above that spot on the river, at all heights. The ones who were
feeding low to the water would be right above that spot, but the duns that
got past those birds would be blown to the south as they rose. So you'd
expect the birds at higher elevations to be farther to the south. This is
the 'diagonal rising zone' of the duns.

In the water, its the same. Imagine a deep pool of slow water, with an
outlet on the downstream side. If there are rising nymphs throughout the
water column in the deep pool, then there are nymphs getting sucked into the
outlet current at all levels. But, a few feet downstream from the pool,
there won't be any nymphs at the bottom; they will have risen a few inches,
so there will be an 'empty zone' along the bottom of the river from that
point on down. Dragging a nymph through that zone will be useless. The
'diagonal rising zone' is the diagonal zone where the nymphs are, starting
at the bottom near the pool and rising to the surface several meters
downstream, depending on the current.

In Wales, all the nymphs I saw swhere I was standing were between 1 and 2
feet below the surface: I looked deeper and never saw one go by at knee
level, and (in an effort to keep my sleeves dry) I tried to find one near
the surface to scoop up, but never saw one shallower than 1 foot deep. Also,
there were no fish rising near me, but they were rising about 10 meters
downstream from me, or in the calm pool above me. I suspect the fish near me
were eating nymphs that were 1-2 feet deep, that the fish 5 meters
downstream from me were eating nymphs that were 6 inches to 1 foot deep, and
the fish 10 meters downstream were eating nymphs on the surface.

--riverman