Ramblings of a catskill fly fisher

Changes in some Catskill tailwater mayfly hatches

By TONY BONAVIST
Posted 7/15/20

Some of my angling friends call this time of year “The Dead Time” because hatches of mayflies and other aquatic insects are on the wane. For the most part, they are absolutely correct in …

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Ramblings of a catskill fly fisher

Changes in some Catskill tailwater mayfly hatches

Posted

Some of my angling friends call this time of year “The Dead Time” because hatches of mayflies and other aquatic insects are on the wane. For the most part, they are absolutely correct in that most spring and summer mafly hatches end by the first of July. That leaves diminutive Trico’s, Blue-winged Olives and fall Isonychia’s on some rivers as the only remaining hatches of the season—at least on freestone rivers.

There is a progression of mayfly hatches each year that follow a pattern of evolution that began thousands of years ago. Each part of the country has its own series of mayflies that hatch in sequence over a period of several months. In the Catskills, our hatches begin with Quill Gordon in mid-April; Hendrickson/Blue Quills at the end of April, March Browns and Gray Foxes around mid-May, and Green and Brown Drakes, if on time, Memorial Day weekend. The first week of June begins with the emergence of Pale Evening Duns (PEDs), then about 10 days later, the eagerly awaited little Sulphur mayfly. At the end of June, there are summer Isonychia mayflies on some rivers and Light Cahills on others. That is the sequence of mayfly hatches on freestone rivers where lower flows and higher water temperatures are the norm.

Hatches on the cooler tailwaters are another story altogether. Due to the release of large volumes of cold water, the timing and duration of some mayfly hatches have changed dramatically over the years. Hatches that historically lasted a week to 10 days now continue over a month on some tailwaters. That is exactly what happened with the PED and Sulphur mayfly hatches.

Due to the impact of cold bottom release water, the PED hatch, which begins around June 1, can be found on some tailwaters well into July. That hatch starts earlier in the day, too, not just at dusk. On freestone rivers, the Sulphur hatch normally begins around June 10. It is an evening emergence with most duns leaving the water right at dusk. On the bottom-release rivers, we found Sulphur hatching at 1 p.m. several years ago! And instead of a 10-day hatch, Sulphurs continued well into August, providing fly fishers with some very welcome afternoon fishing.

For the last 20 years, fly fishers that fish the tailwaters have come to depend on the extended hatches of PEDs and Sulphur mayflies to provide most of the fishing until the Olives start in July. Sadly, beginning in 2016, Sulphur hatches all but disappeared on the upper reaches of at least one tailwater. Sulphurs were absent from that river, again in 2107 and 2108, only to reappear in 2019, but in August with far fewer numbers. In addition, the 2019 hatch occurred late in the day instead of the afternoon.

Anglers that fish this tailwater have grumbled about the loss of the Sulphur hatch since the end of the 2016 season. Justifiably so, because the demise of this little fly not only had a significant impact on fishing opportunities but it is also an indication of a habitat issue—something associated with the river that negatively affects this species.

Those of us that fish the tailwaters are concerned with the loss of the Sulphur mayfly hatch. We have talked about it a lot and speculated about the cause. Some think it is related to the buildup of filamentous green algae along the river bottom, which is prevalent close to the dam where the water is the coldest. The theory is this: The algae is compromising the amount of river bottom available for Sulphurs to effectively reproduce. Yet, other species like PEDs are doing well and still hatching in that area despite sharing the same genus as Sulphurs. Others believe that Sulphurs, like all insects, are subject to cyclic population fluctuations. That theory seems a stretch considering that we are well into the fourth year of Sulphur declines. The only answer is we just don’t know!

At least on one tailwater, the PEDs continue and the little Blue-winged Olives are starting. So, as my old friend, Roger, used to say: “We just have to take what the river offers and be thankful for that.”

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