Q.
From Dcush23315: In the Northwest where I live
and fish we have, for the past two years, been
dumped on with rain and floods. Rivers have been
blown out for weeks if not months. My question
is how can any aquatic insect survive such forces
and will we see a major decline in hatches? If you
are wildly rich or have won the lotto, I may be your
long lost cousin…my last name is Cushing.
A.
I used to live in the Northwest and am familiar
with what you are talking about. However, I wouldn’t
be too concerned about seeing a decline in hatches
for the most part. It is quite amazing to see not
only how many insects actually survive severe floods,
but also how fast streams can become repopulated.
Much depends on how much movement of bed materials
occurred. Both aspects have been widely studied
throughout the world. The Touchet River in
southeastern Washington suffered major flood damage.
When the water receded, I visited a site where I take
my Stream Ecology classes and it was literally a
straight chute devoid of everything except a few
chironomids; bed movement was extensive. This was
in May. By June, the class was able to find an
abundant variety of aquatic insects in the impacted
reaches.
Repopulation comes from a variety of sources (I addressed
this in relation to small cold desert spring-streams
in a paper I published a few years ago). If the
floods occur when egg-laying adults are present,
repopulation is hastened. If it occurs in winter,
repopulation may take longer depending upon the
severity of the flood because egg-laying adults
will have to come from nearby sources. However,
many floods do not impact entire water courses
but only certain reaches, leaving a rich source
of recolonizers in unimpacted reaches above the
flood zone which can drift down and recolonize
the impacted area. It is also amazing how many
aquatic insects actually survive these floods.
They find refuge in the hyporheic zone (below the
stream bed, again, if bed movement wasn’t severe),
behind larger stones not moved by the water, and
some even have enough mobility to actually follow
the rising water edge and then retreat with it when
waters recede. The latter depends on many things;
rate of water rise, nature of the stream bank, etc.,
but does happen in small spring-streams.
I hope this gives you some idea of the complexity
of this. If you’d like to pursue it further, get
in touch with me at cecushing@aol.com. I’m afraid
you are out of luck regarding instant wealth by
relationship. I’m neither rich nor do I know of
any lost cousins! Great name, though.
If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584
Email: streamdoctor@aol.com
The ‘Stream Doctor’ is a retired professional stream ecologist and
author, now living in the West and spending way too much time
fly-fishing. You are invited to submit questions relating to
anything stream related directly to him for use in this Q & A Feature
at streamdoctor@aol.com.
Originally published March 22nd, 2004 on Fly Anglers Online by Robert Younghanz.