Extreme conditions impact fish populations across Texas
By Kathy Wythe
Extreme drought has decreased flows in rivers and streams and depleted major reservoirs across Texas, changing the fish population, even threatening the survival of some rare fish, according to Texas fish experts.
Low or no streamflows cause loss of habitat, degraded water quality and increased saltwater intruding into fresh water.
Cindy Loeffler, Texas Parks and Wildlife Department (TPWD) Water Resources Branch chief, said streamflow gages for much of the state are registering well below normal this year, indicating severe hydrologic drought. She said these low flows are limiting available habitat for some freshwater aquatic species.
“It is probably too soon to know what long term effects the drought will have on fish populations across the state, but biologists are concerned that rare fish will have a tough time surviving the extreme conditions,” Loeffler said.
In the upper Brazos River where some parts are reduced to isolated pools of water or have no water at all, TPWD scientists along with Texas Tech University scientists are trying to salvage two potentially endangered species of minnows—sharpnose shiner and smalleye shiner.
“These fish are a unique part of Texas’ natural heritage,” said Dr. Gene Wilde, a Texas Tech University professor of fish ecology, in a Texas Parks and Wildlife news release. “They’re found only in Texas in the Brazos River and nowhere else in the world.”
“There is a real possibility of extinction for these two minnow species,” he said. “The thing we warn about as a threat could actually come to pass this year because of the drought.”
In September, the scientists collected some of these species and transported them to the Possum Kingdom Hatchery for safekeeping until rain and better habitat conditions return.
Stephan Magnelia, TPWD’s River Studies Program director, said the department had plans to collect more of the two species and move them to the lower Brazos River, but then it rained and scattered the fish. “If the drought continues until next summer, we will collect them and move them to the lower Brazos below Possum Kingdom Reservoir,” he said.
TPWD is also keeping an eye on the Rio Grande chub, a fish species on Texas’ threatened list and only found in one creek in Texas, the Little Aguja Creek in the Davis Mountains. Magnelia said lack of water plus ash from the recent wildfires in the area concerns the department. “It is possible when heavy rains come, ash from the fires will go into the creek and kill aquatic life,” he said, adding that if that happens, the department may need to provide a refuge for the chub.
The TWPD scientists are currently assessing the situation at Little Aguja Creek in cooperation with scientists from other agencies and the Texas Nature Conservancy.
Magnelia said there are also concerns that ash and sediment input from the loss of groundcover from this summer’s wildfires may create problems for aquatic life in the Llano River near Junction and the Colorado River near Bastrop when heavy rains return.
Winemiller said his research group is seeing major changes to the fish community structure in rivers and streams because of the drought. “For example, in the Brazos River below Waco and towards the coast, the composition in our samples is different,” he said. “The same species are present as before but the ones that dominate are different from what we usually find in a normal year.”
Winemiller said they are seeing many more “predators,” such as bass and catfish, which are reproducing successfully with the drought, and fewer minnow species that are river-channel specialists. These minnows only live in the channels or main stems of rivers, not in streams or lakes.
“We think the predators are really decreasing the population of these river-channel specialists,” Winemiller said.
Flows in the lower Brazos have been relatively stable during the drought because of regular releases by the Brazos River Authority to fulfill a permit requirement downstream. These steady low flows favor the predators’ reproduction and recruitment, the number of juveniles joining the population, Winemiller said.
Low flows and high temperatures are also affecting the water quality of many of the state’s rivers. Stable flow without the normal fluctuations in the river’s levels allows excess nutrients to remain in the water, encouraging algae growth, which leads to lower levels of dissolved oxygen. Low dissolved oxygen levels kill fish.
Loeffler said numerous fish kills have been reported throughout the state because of low dissolved oxygen levels.
Winemiller said he has found higher salinity and lower dissolved oxygen levels in the lower Neches River in East Texas because of the drought and low flows. This year saltwater has moved upstream from the Gulf and has reached a saltwater barrier located north of Beaumont to prevent further intrusion and degradation of the city’s water supply.
He said his group recently measured the salinity in the lower Neches River at 15 parts per thousand, much higher than normal. With this increased salinity, marine fish are moving into the river.
“That is not necessarily a bad thing,” he said. The problem with the increased salinity is the likely damage to the region’s bottomland hardwood forests comprised of species like bald cypress and water tupelo. “Those trees can’t tolerate those kinds of salinity,” he said. “This year is going to be really hard on the bottomland hardwood vegetation communities along the lower Neches.”
Winemiller said their measurements of oxygen saturation in the lower Neches River further illustrate the drought’s effect on the river’s water quality. Water flow is so stagnant where a paper mill discharges its effluent into the river, the water is black, he said.
“There is no flushing because of the saltwater barrier and no flow at all coming out of the tributaries,” he said. “We measured dissolved oxygen from the main channel and the percent saturation ranged from 42 percent to 85 percent. Normally you would expect to find around 100 percent saturation of dissolved oxygen in a river, so that is degraded.”
With the prediction that the drought will continue through 2012, the scientists believe the fish population will continue to be impacted.
Besides the obvious fish kills when a reservoir like O.C. Fisher in West Texas is almost dry, Magnelia said if the drought continues reservoirs may lose their connection to the rivers that feed them. This will keep migration species such as white bass from spawning up river, decreasing their populations.
The good news, Magnelia said, is terrestrial vegetation has grown up in reservoir and riverbeds with the lower water levels. “Once the water goes up again, this vegetation will provide good habitat for many species of juvenile fish, so we should see a pretty quick rebound in populations,” he said.
With more than 180 species of native freshwater fishes, Texas ranks among the most biologically diverse states. “But approximately 40 percent of Texas fishes are now already extinct or risk regional or even global extinction” Loeffler said. “Texas already ranks in the top five states for numbers of endangered aquatic species. If the drought persists into 2012 and beyond, this situation could worsen.”