Lake Wylie Dam

Great Blue Heron

Effects of Hydroelectric Operations on Fish-eating Birds

For years I have enjoyed fly-fishing. When I lived in Arkansas, I fished in the tailwater fisheries below dams on the White River. Wading in the water below Bull Shoals dam in the middle of summer when the air temperature is over 90 degrees, the water in which I was standing rarely topped 50 degrees as my wadered, but numb legs would testify. This was my first realization of how hydroelectric operations could affect life below dams.

<>Probably because hydro operations are highly regulated by the federal government, much research has been devoted to the effects of dam operations on water quality, invertebrates and fish.  Virtually no research, however, has been conducted to determine the effects of hydro operations on birds and mammals that eat fish. I am currently conducting research to determine the effects of altered flow regimes on foraging of great blue herons. Herons are visual feeders and they forage on fish near the surface. Also, they most often stand or walk in the water to find fish, thus water depth is critical to their foraging success. In coastal areas where water depth changes with the tide, great blue herons feed primarily at low tide when water depth allows better access to fish. 

<>The Lancaster area is an excellent place to study the influence of dams on wildlife. The Catawba River is one of the most intensely regulated rivers in the country. There are six dams within a 30-mile radius of Lancaster and one of the only free-flowing parts of the river is within 5-10 miles of the USC Lancaster campus. Dams differ in their pattern of generation and, consequently, in the amount and timing of water they release, but changes in water depth and velocity can be striking. Water depth can vary a meter or more within and hour. For a heron, high water can virtually eliminate the possibility of catching fish and, as with the tide, likely will determine when herons can forage—or at least when they can forage on the main stem of the river. Thus, for herons foraging below a dam, the operations of the dam determine daily patterns of foraging which influence when and how often nestlings get fed, and possibly even the group size of heron colonies. 

<>My study currently focuses on great blue heron foraging patterns at various points below the Lake Wylie Dam south of Charlotte, North Carolina. I am also looking for heron colonies in that area to get an idea of where and how much the herons move during the day to find food. I believe that herons follow the falling water downstream after generation is shut off. If this is true it opens up more questions such as how far do herons travel down the river? If they don’t stay on the river during high water, where do they go? This system may also be valuable in addressing some ecological and behavioral theory related to foraging and predation, and also the reason that herons nest communally. Future research may also focus on other species of piscivorous birds, such as other herons and egrets or the small but bold kingfisher. 

<>This research lends itself well to student involvement at many levels; from being a field assistant to developing an independent project. Please contact me if you are interested.