Drought and the trout fishery

Posted 9/14/22

Note: For all the rain we received recently, as of September 10, most of our region is still abnormally dry or in a moderate drought, according to www.drought.gov/states/new-york. Tony Bonavist, who …

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Drought and the trout fishery


Note: For all the rain we received recently, as of September 10, most of our region is still abnormally dry or in a moderate drought, according to www.drought.gov/states/new-york. Tony Bonavist, who writes a fishing column for the River Reporter, explains why drought matters for our rivers and for the trout fishery that is a significant part of the local economy.  

Beginning in the spring of this year, streamflow has been a mixed bag, for the Catskills freestone trout rivers. By freestone, biologists mean all those naturally flowing watercourses that depend on rain and runoff for flow. That differs from tailwaters, where flow and water temperature are modulated by the release of cold bottom-water from reservoirs.

The spring of 2022 began with a large amount of rainfall, which left reservoirs spilling, and stream flows in the thousands of cubic feet per second (cfs). For example, the combined spill and bottom releases from the Pepacton reservoir, recorded at the Downsville gage, measured at 10,000 cfs on April 5. As a result, the East Branch of the Delaware River remained abnormally high until the second week of May.

Despite all the rain in April and May, precipitation in June fell by 0.63 inches, in July by 1.87 inches and in August by 2.18 inches, for a total of 4.68 inches below average. At the same time, storage in the New York City Department of Environmental Protection’s reservoirs measured 74.8 percent of capacity, compared to 86.8 percent for other years.

So 2022 has been feast or famine when it comes to water. Too much in spring, and semi-drought conditions from June onward.

What impact do drought and low stream-flow have on the region’s freestone trout fisheries?

First of all, brook trout are found mostly in the well shaded, cooler tributaries, and have survived all manner of weather-related issues for thousands of years. However, once water temperatures reach 68 degrees Fahrenheit, brown trout in particular seek cooler water. Rainbows seem to be a bit more temperature tolerant. Nevertheless, once water temperatures reach 70 degrees Fahrenheit, trout begin to stress, and if they cannot find refuge, mortality can occur as temperatures exceed 75 degrees Fahrenheit without respite.

Keep in mind that as water temperatures rise, water loses its ability to hold dissolved oxygen. As a result, trout are not only confronted with increasingly lethal water temperatures, but face lower concentrations of dissolved oxygen as well. A double-edged sword.

So how do trout survive unfavorable environmental conditions?

Where rivers feed a deep lake, trout will migrate to the cool depths of that lake. In strictly riverine environments, trout will find cool spring holes, which are present in almost all trout streams. In addition, there can be significant differences in diurnal temperatures, which means that air and water temperatures can cool by as much as 10 degrees overnight. That does help, and provides some relief to those trout continuously exposed to high water temperatures and reduced dissolved-oxygen concentrations

From what I’ve learned over the years, speaking with knowledgeable folks about the impacts of low flow and warm water on trout populations, is that those conditions affect the fishing more than the fish. (It is not legal or ethical to fish in some rivers, when trout are under stress.)

It may sound odd, but it appears that despite all the unfavorable conditions that our Catskill trout are exposed to, they always find a way to survive. Next spring, the rivers will rise, the flies will hatch; trout will rise. The fishing and life cycle of trout streams continues.

trout populations, drought, Catskill trout


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