Are the Sulphur Mayflies back?

Posted 8/14/19

Though they’re extremely late, they are back, at least for this season. The hatches normally begin the second week of June. Sulphur mayfly hatches have been absent or limited in numbers from …

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Are the Sulphur Mayflies back?


Though they’re extremely late, they are back, at least for this season.

The hatches normally begin the second week of June. Sulphur mayfly hatches have been absent or limited in numbers from some Catskill Rivers since 2016. That is when anglers began reporting the species’ decline. For those of you who read “Another Silent Spring,” my article in this year’s River Reporter magazine Fish, will recall that I referred to the species decline in that piece. At the time, we attributed the loss of Sulphur hatches to the buildup of dead leaves and rooted aquatic vegetation along the river bottom as the cause. The river had not been flushed since 2013 and, as a result, there was consensus that all the dead and decaying leaves had compromised the habit needed for the species to survive and thrive. When the river did flush in 2018 and 2019 without response from Suphurs, we were all a bit baffled as to what the cause of their demise really was.

Anyway, during the last two weeks, the word went out: “The Sulphurs are hatching again!”

So on August 6, I had the opportunity to see, firsthand, a very good hatch of these little mayflies. There were a lot of flies on the water. The trout fed steadily through three heavy rain showers, combined with rumbles of intermittent thunder. I’d like to be able to say that, during that period of heavy feeding, a lot of trout came to my flies—they didn’t. Although there were hundreds of Sulphurs on the water, the trout were taking emerging flies, as the nymphs made their way toward the surface. I did have some success using a pheasant tail nymph, tied “parachute,” designed to float in the surface film. It worked, to a degree, but was definitely not the answer. So it’s back to the fly-tying vise.

Our little Sulphur (Ephemerella dorothea) is one of three eastern mayflies called “Sulphurs.” The other two are actually pale evening duns, hatch earlier in the season and are much larger. I wrote about the three species in the August 16, 2018 edition of The River Reporter. It explained the differences in those three species, when they hatch and the difference in size.

In freestone rivers, Sulphur mayflies hatch at dusk, and leave the water immediately, and more often than not provide little fishing opportunity. Hatches on freestone rivers may last two weeks. On the tail water, some years ago, however, we found very large Sulphur hatches occurring around 1 p.m., about two miles below one of the reservoirs, where the water temperature is always in the low 50s. Because of the releases of very cold water from those reservoirs, Sulphurs hatch during the day and not in the evening. So instead of what was a two-week hatch, is a two-month hatch, providing anglers with angling opportunities not found on freestone river. Those hatches lasted well into the evening, and sometimes extended into mid-August. And even though anglers had difficulty rising trout during Sulphur hatches, the little flies were eagerly awaited by fly fishers. Our little Sulphur, although the target of a lot of discussion and frustration among anglers because of the difficult fishing they cause, was sorely missed when hatches disappeared from Catskill tail waters for several years.

So for this season at least, the Sulphur hatches are back. Hopefully, the tail waters in question will see enough annual runoff to flush the rivers, keeping the bottom free of the organic debris that compromise the habitat necessary for these prolific little flies to continue to hatch each year and contribute to our fishing. Let’s keep our fingers crossed that’s the case.


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