Muf,
You bring up two interesting points. The first - where are the bugs
going, followed by why aren't we using patterns to match the bugs
that are there? I've thought about your post and would like to
remind the list two things: 1)I used to be smart and 2)I'm an Idiot
(I'm reminded daily by the woman I live with).
I believe all things move in one cycle or another. Bugs that we
imitate aren't much different. The life cycle is the most well
known. As fisher-folk, we have books and charts and time tables and
web sites all mapping out hatch and spinner falls. The bonus
features of some places would tell you what are the best water temps
and clarities and every other nuance of water quality needed as
well. We know or have come to expect certain bugs at certain times
of the year. What the books of 20 years ago don't account for are
disasters of natural or man-made proportions. Hurricanes like
Katrina of this year, or Ivan of 2004 change the number of nymphs in
the water. They also move or kill or at least change the number of
preditors at that time as well as food for the smaller creatures too.
Hurricanes and Floods are an easy thing to recognize as far as
forces that move both fish and bug. Large amounts of water rushing
downstream spread downstream fish and their food, creating various
imbalances throughout the stream or river. Not every thing moves
downstream and not everything moves the same distance. This also
allows for the cross breading of sub-sub-sub species of a particular
fly. Ever notice that slight variations of the same pattern produce
differently on different stretches of the same watershed? Or as you
mentioned Muf, the March Brown w/Orange Herl for Year X where orange
wasn't part of the equation for year X-1? What caused the change in
the bug? The fish are keying in on part of the bug or something new
to the bug that year, something caused it.
Other things that may cause bug kills or movement can be droughts
that cause the water level to fall below sustainable levels for the
biomass of the stream level to sustain. Less food for the bugs means
fewer bugs. Fewer bugs lead to fewer fish, either through fish
movement or death. Eventually the balance returns and there's more
food for the bugs, and the cycle goes the other direction. Wild
animals and 'tame' animals can destroy bug habitat in the stream with
out expressly meaning to as well. The swans in your story did that
very such thing by eating the water crowfoot, thereby destroying bug
habitat. Don't forget natural preditation - both in the water and on
land/air. If a large number of fish end up in an area with a small
hatch or bug population, they can easily destroy their food
sources. Birds and bats and other insect feeders can just as equally
destroy small populations while the mayfly is in it's dun/spinner life cycle.
Of course NONE of the above addresses the numerous man-made
possibilities than can exist. In Western Pennsylvania, acid rain and
acid mine drainage are both damaging to water quality leading to poor
stream biomass (bugs AND fish). Threats by former mine owners to
shut down the pumping water out of various mines, leading to stream
flooding with excess acidity blowing down a stream and wiping it all
out. That's just ONE sample of man-made disasters, we've read about
others that I'm not going to discuss.
Part II to come.
-->Garry
