TPWD News Release — Sept. 21, 2011
Fish kills due to low oxygen levels have been documented on the lake since 2003. These kills have resulted in the loss of an estimated 2,719,096 fish valued at $6,120,263.79.
“The total kill for 2011 is much lower than the nearly 1.5 million killed last year,” said Richard Ott, TPWD fisheries biologist, who manages the lake. “It is very likely the reduction in number of fish killed is attributable to a reduction in the number of fish present. Furthermore, the size distribution of fish killed this year suggests that most were young. The long-term prognosis is that without some substantial change in water quality, annual kills will continue, and these populations will no longer be self-sustaining.”
Texas Parks and Wildlife Department (TPWD) Inland Fisheries biologists have determined that the low oxygen levels result from a combination of factors.
Normally microscopic plants called phytoplankton produce oxygen by photosynthesis during daylight hours and increase oxygen concentration enough to compensate for respiration (oxygen use) by those same phytoplankton and fish as well as bacterial decomposition. However, during periods of cloudy weather, sunlight (measured as solar radiation) is reduced; oxygen consumption remains high but oxygen production is greatly reduced. When cloudy weather lasts for several days and oxygen concentration falls below the minimum level to support aquatic life, fish begin to die.
In late August and September, water temperature and bacterial activity are still high but day length shortens incrementally. In power-plant reservoirs such as Fairfield, water temperature and day length can become out of phase and increase the probability of fish kills.
Similar fish kills have also been reported in the past at other power-plant lakes such as Victor Braunig and Calaveras near San Antonio but were of much lower magnitude than those at Fairfield. The situation at Fairfield is exacerbated by the fact that the make-up water pumped into the reservoir from the Trinity River to maintain elevation is very high in nutrients. These nutrients are further concentrated due to evaporation and lack of water discharge through the dam. This high level of nutrients contributes to high phytoplankton and fish production in Fairfield Lake but also contributes to dissolved oxygen depletion during cloudy weather.
Ott will be making recommendations to Luminant on how to correct the problem, but in the meantime, TPWD plans to suspend stocking fish into Fairfield Lake. “The fish we produce in our hatcheries are limited, and stocking them into a reservoir where they will have very little chance of survival is not our best use of them,” Ott said.
Fairfield Lake has long been known as an excellent largemouth bass fishery and more recently as a trophy red drum freshwater fishery, but it also supported populations of forage species as well as catfish and tilapia. All these fisheries appear to have been impacted by the kill. “By using datasondes we were able to verify levels of oxygen below what will sustain fish even in the middle of the lake, where water quality is expected to be the best,” Ott said.
Additional information about the kill and comparative size distribution of fishes involved is available on the Inland Fisheries District 3-C Facebook page at http://www.facebook.com/TPWDIFTyler
Questions about the Fairfield Lake fishery should be directed to District Biologist Richard Ott at (903) 566-2161, firstname.lastname@example.org.