Drought threatening wild trout survival
State College, Pa. — If this year seems to you to be extremely hot and dry, it’s because it has been. If you are worried about how the parched conditions are affecting wild trout waters, you are justified.
The driest region of the state is the northcentral region, where most of the state’s wild brook trout streams are located. On Aug. 2, the state Department of Environmental Protection put 34 counties under a drought watch and placed Potter County under a more severe drought warning.
According to Bryan Swistock, a water resources expert with Penn State Extension, National Oceanic and Atmospheric Administration, records show that for northcentral Pennsylvania, July was the fifth driest on record and the 13th warmest.
For the year-to-date (January through July), it has been the fourth driest and 13th warmest.
For the entire state, the year so far has been the 11th warmest and the 21st driest.
“I hate to use the word serious because we are still sort of on the cusp of what’s going to happen with this drought. It is a developing drought but it is not tremendously serious at this point,” he said.
“Probably the biggest impacts so far have been agricultural. Stream flows, especially in the northcentral region, have been extremely low and conditions are actually worse as you go up into New York and over into Massachusetts.”
On Aug. 13 Swistock noted that parts of the state had finally received some heavy rains in the previous few days, including Potter County, but long-term weather forecasts for Pennsylvania are discouraging. Much of the state faces rainfall deficits of 6 inches or more.
“In the next week or so we have a lot of opportunities to get rain, but the long-term forecast for the fall calls for it to be dry and hot after late August,” he said.
“The forecast for August, September and October is for warmer than normal temperatures and near normal precipitation.”
Moving to protect wild trout beset by high water temperatures and low stream levels, the state Department of Conservation and Natural Resources and the Pennsylvania Fish & Boat Commission temporarily posted two sections of Penns Creek to prevent fishing and disturbance of massed fish by passersby.
“The prolonged combination of little rainfall and steadily climbing water temperatures has left wild trout massing at two locations in Bald Eagle State Forest where mountain streams are supplying needed oxygen and cooler water,” said State Forester Dan Devlin.
“The goal is to prevent additional stress by limiting angling pressure and the chances of others needlessly spooking them.”
Both located in Mifflin County, not far from the Union-Centre County line, the posted areas affording trout thermal protection are along Penns Creek at the mouths of the Panther Run and Swift Run tributaries.
As temperatures soared and stream levels dropped, trout have increasingly sought out these tributaries’ cooler waters.
The last time Penns Creek was placed under similar regulations was in 1999.
Jason Detar, chief of the Fish & Boat Commission’s Division of Fisheries Management, noted that there aren’t many larger streams in the state that still hold wild trout, and among those, Penns Creek is a special case.
“At this point in time we are not aware of any major issues occurring on any other waterways, and the others are different from Penns Creek in that they receive more groundwater recharge throughout their length than Penns Creek does.”
The three other big limestone streams with wild trout are Spring Creek in Centre County, the Little Juniata in Huntingdon County and Fishing Creek in Clinton County.
Spring Creek is fed by a number of large springs throughout its length that cools its flow, Detar explained, and the Little Juniata River receives a number of large spring inputs in its middled reaches before Spruce Creek joins the river.
“Fishing Creek goes dry and the water goes subterranean in the upper end of the watershed, he said. Going underground, it cools the flow so if there are any elevated temperature problems they are alleviated.”
What makes Penns Creek more susceptible to these warmer temperatures is that in a hot, dry summer such as this, the volume of water coming out of its tributaries is greatly reduced compared to the flows coming from limestone springs.
“So Penns Creek – compared to the other big three really popular central Pennsylvania limestoners – is much more susceptible to elevated summer water temperatures.”
Detar pointed out that this summer’s drought follows two wet years with above-average stream flows and good conditions for wild trout. Fish populations in smaller streams, especially freestoners in the mountains, can be affected by summers like this.
“We certainly can see elevated water temperatures in the headwater streams, but wild trout have evolved to be able to survive through extreme conditions,” he said. “However, we do see fluctuations in population levels in wild trout in response to environmental conditions.”
In a very low-flow year, portions of small streams dry up and the following year wild-trout populations may be reduced. But they usually go through a natural rebuilding process in coming years.
The longer the drought, the greater the chances for higher-level impacts to wild trout populations, Detar pointed out. As small stream flows get lower, the potential for predation from raccoons, blue herons or other predators is greater. And trout can get stranded or succumb to increased water temperature. “Headwater streams are not the easiest environments to survive for trout but, obviously, they have evolved to adapt to these conditions,” he said.