PALE MORNING DUN
| Editor's Note |
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| The following article is part of a series that will we will be running over the next few weeks. |
The fabled Pale Morning Dun hatch is one of the largest and most wide spread of the western hatches. The only hatch that is larger and more widespread is the Baetis Hatch. The term Pale Morning Dun or PMD was coined during the 1960’s by the late Carl Richards and Doug Swisher, the authors of “Selective Trout,” which was published in 1971.
The purpose of this missive will be to educate the angler, to help gain an understanding into world of the Pale Morning Dun, the insect, and the trout that feed on them. From May to October somewhere in the west there are PMD Hatches. All year long we look forward to these PMD Hatches of Summer. We talk about it; we read about it, we tie flies for it. We review patterns and try to construct imitations, which we think will be effective.
However, there are no killer fly patterns that will always work. But there is knowledge and observation!!! Due to the abundance and availability of this mayfly the trout feed heavily on all stages. Therefore, let’s go look at the insects. I have been guiding in the greater Yellowstone area for more than 30 years and have been fishing these waters for a longer period and many of my favorite rivers enjoy excellent hatches of PMD’s.
If you will take a moment to flip back to the Bibliography you will find that besides my own observations, I have researched this topic and have drawn on a number of authors in an attempt to share the combined knowledge and insight on this subject.
In the greater Yellowstone area there are three species of PMD’s
Order: Ephemeroptera
Family: Ephemerellidae
Genus: Ephmerella
Species: Ephemerella infrequens 7mm to 9mm Size 14-16
Species: Ephemerella inermis 5.5mm to 7mm Size 16-18
Species: Ephemerella lacustris 3.5mm to 5.5mm Size 18-20
Except for their difference in size it would be impossible to tell the three species apart in the field, and there is no reason to do so. You need a microscope to identify the individual species.
The reason for the use of scientific names is to exclude any confusion.
My uncle, who was one of my fly fishing mentors, told me “It is not how many hours a day that you fish, but how many hours you fish effectively.” As you read through this paper I hope you gain a more substantial understanding of that statement.
Of the three species of PMD’s found in the greater Yellowstone area, the two most encountered species are E. infrequens and E. inermis. The E. lacustris is found only occasionally on Armstrong’s Spring Creek, on the Upper Yellowstone River and Yellowstone Lake in Yellowstone National Park and in the Jackson Hole Area.
Sometimes anglers will confuse Heptagenia and Epeorus species with the PMD’s. Often these species generally represent the Pale Evening Duns. This is especially true of the Duns. But the nymphs would never be confused.
PMD Nymphs are classified as crawlers. They inhabit medium to slow sections of rivers, they inhabit gravel runs, sandbanks and are found among the protection of the weed beds. PMD nymphs molt up to twenty plus times during their yearlong life cycle. As they mature towards emergence the wing pads become almost black.
Nymphs feed on the thin layer of growth that covers the bottom, the rocks and on decaying vegetation that is trapped on the bottom of the stream. The term “you are what you eat” really does apply to PMD’s. The color of the PMD nymphs can vary widely not only on a stream-to-stream basis, but the color can also vary within the stream. I have seen up to five different color variations on DePuy’s and Armstrong Spring Creeks. PMD nymphs will live and thrive in a wide variety of current speeds and bottom types. Their colors tend to mirror their habitat. The colors are determined by the chemical make-up of what the nymphs are feeding on in their habitat. The colors will vary from pale olive, tan olive, med olive, dark olive, brown olive and an almost blackish brown. I recommend carrying pale olive, dark olive and brown olive imitations. (Patterns will be discussed in another section.) The nymphs are a cross between chunky and streamlined and have three tails.
There are plenty of books, which explain how to identify PMD nymphs, so that is not a subject we will be tackling in this paper.
When dislodged from the bottom, the nymph will drift with the current and they slowly try to swim back to the bottom. Note that early in the season the nymphs are larger and as the season progresses the nymphs will become smaller. PMD nymphs also go through behavioral drift. This is where the insects leave the bottom and drift downstream. The reason for this drift is a search for food. When the nymphs mature they leave the bottom and slowly drift and swim to the surface where they emerge. The duns leave the water rather quickly, especially on warm days. The duns will spend 24 to 36 hours in the bushes and streamside vegetation where they molt becoming a spinner. Then in the low light of early morning or late evening the spinners go through a mating flight where they end up over the riffles and fall on the water laying eggs and dying.
All stages are available to the trout; the nymphs, emergers, duns and spinners. However, not all stages are easily available to the trout.
More notes on the Hatch and other items
The emergence times of the PMD hatch will vary widely between river systems. Therefore, local knowledge is very necessary if the angler is going to properly pursue the PMD hatch. Even with local knowledge there are several factors, which can influence the emergence times. According to Malcolm Knapp and Robert Cormier in their book “MAYFLIES” published in 1997, “They state that the E.infreguens are the first PMD’s on the water as the run-off declines and the water temperatures rise and stabilize into the 50’s.”
The PMD’s E. infrequens are the largest of the PMD’s with the sizes ranging from 13 to 16 Normally the PMD’s will hatch between 10AM to 1PM, cooler water temperatures from a late spring storm could delay the hatching times. This would not apply to the Paradise Valley Spring Creeks, as the water temperatures are always stable at 51 degrees. Therein lays one of the mysteries of fly fishing. What causes the hatch to start on Spring Creeks or Tailwaters. There are many factors, which can influence the hatch: weather cycles, not only seasonal, but even daily, weather cycles can effect hatching times,the hatching can start as early as 9 AM or as late as 3 PM.
Now we will discuss the PMD hatches as they relate to the Spring Creeks of Paradise Valley. There are many factors, which can affect the hatch. Normal weather cycles will bring normal hatches with the emergence beginning around 10 AM early in the season as the season progresses the hatching times will drift to 11 AM and on to 12 Noon, and then even as late as 1 PM. However, hot weather extremes and prolonged hot weather, may cause the hatch to trickle, coming off in steady but small numbers for a long of time. Often during this time period anglers are frustrated. They often leave before the spinner fall, which can be exceptional fishing!!
One true fact that all anglers must understand is that the TROUT FEED ON THEIR SCHEDULE NOT ON OURS. The hatch can also be affected by the up and down cycles of insect populations and the overall health of the stream. A cool break in the weather can back up the hatch times until later in the day. On cool days the hatching duns will often ride on the water for a long period of time making the duns prime targets for the trout. The actual emergence for the PMD can be an event filled with danger with many duns failing to escape the nymphal casing, becoming stuck in the shuck. In addition, wind and river currents also take their toll during the hatches on various types of spent adult duns and cripples. On hot or warm normal days the PMD’s swim to the surface of the water and leave very, very quickly thus making them poor targets for feeding trout.
As normal hot days bring fast hatching duns, extreme, prolonged warm days bring morning spinner falls. For a great many seasons the PMD spinner falls on the Paradise Valley Spring Creeks always occurred during the late evening hours. (Note on some rivers there are notable PMD spinner falls, during the early morning hours 7AM to 8AM). However it has only been during the past several years during drought conditions that we began to see spinner falls during both the mornings and evenings. The spinners collect over the riffles and then begin to fall on the water. The anglers may also encounter spinner falls during the afternoon, when clouds build up prior to a thunderstorm. Thus the angler needs to be observant and make sure that the spinner imitations are always on hand.
Part 1 of a series
Addendum:
Listing of Rivers which have PMD Hatches in the Greater Yellowstone Area
Boulder River, Mt-------------------------------------------------------------July and August
Kootenai River, Mt-------------------------------------------------Mid-June to Late August
Flathead River, Mt--------------------------------------------------Mid-June to September 1
Yaak River, Mt---------------------------------------------------------June 1st to August 31st
Swan River, Mt------------------------------------------------------July 1st to mid-September
Clark’s Fork River, Mt-----------------------------------------------------July 1st to July 31st
Rock Creek, Mt----------------------------------------------------Mid-June to September 1st
Bitterroot River, Mt-------------------------------------------Late May to Early September
Lolo Creek, Mt-----------------------------------------------------Late June to Late August
Blackfoot River, Mt----------------------------------------------------------July and August
Bighole River, Mt--------------------------------------------------------Mid June to August
Beaverhead River, Mt-----------------------------------------Mid June to August 30th
Madison River, Mt--------------------------------------------------------July & August
Gallatin River, Mt---------------------------------------------------------July & August
East Gallatin River, Mt---------------------------------------------------July & August
Missouri River, Mt--------------------------------------------Mid-June to Mid-August
Smith River, Mt------------------------------------------------Mid-June to Mid-August
Yellowstone River, Mt (Paradise Valley--------------------------July to Mid-August
Big Horn River, Mt---------------------------------------------Mid-July to Late August
Big Spring Creek, Mt-----------------------------------------------------July and August
Silver Creek, Id-----------------------------------------------------------Late June to July
Firehole River, Yellowstone National Park------------------------Mid May to July 10
Madison River, Yellowstone National Park---------------------Mid June to Mid-July
Henry’s Fork of the Snake, Id------------------------------------June 1st to August 15th
Upper Yellowstone River, Yellowstone National Park---July 15th to September 5th
Slough Creek, Yellowstone National Park-----------------------July 1st to August 1st
Armstrong’s Spring Creek, Mt---------------------------------June 15th to August 25th
DePuy’s Spring Creek, Mt--------------------------------------June 15th to August 25th
Nelson’s Spring Creek, Mt--------------------------------------June 15th to August 25th
This information comes from some of my own hatch charts and from Greg Thomas’
Fly Fishers Guide to Montana.
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