Western March Browns
.............................Fly Fishing Yellowstone National Park
05/22/08

Western March Browns - (Rhithrogena sp)

The Western March Browns are species of the Rithrogena genus of the Heptageniidae
family of mayflies. They are among the first mayflies to hatch in Yellowstone National
Park. The hatches depend greatly on the unpredictable weather of the early season,
but usually are fairly heavy and condensed into a short period of time.  The “Western
March Browns” inhibit the fast waters of riffles and runs of the streams but are
occasionally found in the slower to moderately moving water.
The
morrisoni species is the first to hatch, and may be followed by the hageni within a
few weeks. The
morrisoni hatch can occur when some of the streams are blown out
from the runoff. The
morrisoni is usually found in moderate to fast moving water, but
slower than the
hageni that prefers fast streams.
The
futilis and undulata species usually hatch in the summer months and as late as
early Fall. These hatches are usually not very prolific and may be short and scattered.
The duns hatch off and on for a few hours and are rarely concentrated but the spinner
fall may be compacted into a shorter time and dense. It is usually the best stage to fish.
Both of these species can be found in moderate to slower moving water than the other
two species are usually found in.  
We have only found a very few occasions that we have been able to fish the Western
March Brown hatch. Most of those occasions occurred during the spinner fall of those
species that hatched in the summer and early fall. We do not want to over state the
importance of this hatch. We have only been able to catch a few fish as a result of it.
This may have been a product of just not being at the right place at the right time.
Yellowstone is so huge, has so many streams and options, we may have just not come
across a big hatch even though we have fished the park extensively  for the last eight
years with the exception of one year. On the other hand, if you happen to encounter a
hatch, we want you to be prepared for it.   

Nymphs:
The Rhithrogena nymphs are classified as clingers. Sometimes imitations are effective
but this is usually only during the time when the nymphs are migrating from the fast to
slower moving water to emerge. Otherwise, most of the time the nymphs are down
between or under the rocks on the bottom of the stream.

Presentation:
If you do try fishing imitations of the nymph, you should fish them on the bottom in a
dead-drift fashion using plenty of non-toxic weight. Concentrate on the pockets and
seam edges of the faster moving water.

Emergers:
The early hatches usually occur during the warmest part of the day, from 1:00 PM to    
4:00 PM. The summer hatches usually occur during mid-day. The late summer, early
fall hatches usually occur during the warmest part of the day like the early hatches. Like
the nymphs, imitations of the emerging March Brown imitations don’t always work. It  
depends on the time of the year, the particular stream and the particular
Rhithrogena
species. In the colder water normal during the early part of the season the trout may
take wet imitations fished well below the surface. Later in the season, you may try
fishing the imitations near the surface, but don’t waste a lot of time trying if you are not
getting good results.

Presentation:
Since the nymphs migrate to the slower moving, calmer water near their fast water
habitat, those are the areas you should concentrate on. You should fish the wet
imitation of the emerger with a dead drift or the swing type presentation.

Coming Up Next:
Western March Browns - (Rhithrogena sp) - Duns and Spinners

Copyright 2008 James