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Task force members dig into hydrilla problem

Tuesday, November 27, 2012 by Charles Boisseau

Members of the Lake Austin Task Force on Monday delved into the murky waters of hydrilla, the invasive vegetation that has become a growing menace to boaters, residents and users of the lake.


This July, shortly after Austin City Council formed the task force, hydrilla reached an all-time high, covering 580 acres of the lake with thick mats of vegetation, up from 350 to 450 acres in mid-2011.


In a briefing to task force members, Mary Gilroy with the city’s Watershed Protection Department said that the increase was likely because of the ongoing drought, which has created ideal conditions for hydrilla, which prefers warm water. Since the Lower Colorado River Authority has limited water releases from Lake Travis for downstream irrigation, there’s less cool water flowing through Lake Austin, contributing to hydrilla growth.


Moreover, Gilroy said that the city’s efforts were hampered because high demand throughout the South caused a shortage of sterile grass carp this summer, slowing the plans to release more fish.


“We just didn’t have enough fish in the lake,” Gilroy said. 


The shortage of carp has let up, and as recently as Nov. 6, the city placed 6,000 more carp into the lake at a cost of $30,000, or $5 a fish, she said. City staffers say the stocking will replace fish that have died naturally and is intended to maintain a target population of 50 fish per acre of hydrilla, a rate now seen as ideal for controlling hydrilla and more than twice the target once thought as ideal a few years ago.


All told, since 2003, the city and its partners, the LCRA, the Friends of Lake Austin and the Texas Parks and Wildlife Department, have released roughly 40,000 grass carp into Lake Austin, with more than 30,000 of those in 2011 and 2012, all under a required permit from the Texas Parks and Wildlife.


While the amount of hydrilla has seemed unstoppable of late, the most recent survey by state scientists in September gave a sign of relief: a slight decrease to 560 acres of hydrilla found in Lake Austin.


Still, that dip was hardly significant, said Ellen Witt, a task force member, who was among several members who quizzed Gilroy during her hour and twenty minute briefing and Q&A. “What if it spikes again?” Witt asked, saying that now is the time to consider whether more aggressive measures are needed.


“We considered it to be a crisis when it was half this amount,” Witt said.


Witt asked Gilroy and Earl W. Chilton II, director of the Texas Parks and Wildlife’s Aquatic Habitat Enhancement Program, whether another survey could be done soon, perhaps early 2013. The state had not planned another survey until next spring. Chilton responded that the state might be able to move up its next scheduled survey to February or March.


Witt asked Gilroy if the city could reserve 2013 carp ahead of time to ensure Lake Austin has a supply when needed next spring and summer.


Gilroy said she was unsure whether the city could reserve carp, though she said she could investigate. She noted that supplies were short because several other southern states purchased a total of 200,000 to 300,000 carp from the Arkansas hatcheries where they are raised.


Sterile grass carp are seen as the most effect way to limit hydrilla, Gilroy said. Mechanical harvesters and herbicides are other options, and can get rid of hydrilla more quickly than carp can eat it, but Gilroy said these methods are expensive and generally less effective. Moreover, Austin residents have generally been opposed to using chemicals no matter how safe they may be to human health.


Even so, Gilroy said grass carp are not a magic bullet, and the solution takes time to provide results. The young carp are about 12 inches long when released into the lake from Mary Quinlan Park and need time to grow and feed.


“We just put 6,000 fish in the lake November 6,” Gilroy said. “We’re not going to get rid of it in a month. It’s going to take some time.”


Chilton also noted that officials managing Lake Conroe, a reservoir near Houston that has a long history of combating hydrilla, have now found that 55 carp per acre of hydrilla is ideal amount to control the vegetation, thus possibly giving an opening for those who want more carp in Lake Austin.


Hydrilla isn’t the only invasive species in the lake. Eurasian watermilfoil, sometimes called duckweed, has been in the lake even longer, dating to the 1960s or 1970s and possibly longer. But milfoil is fairly easily controlled and only grows in water depths of 12 feet or less.


In contrast, hydrilla “is a pretty tough plant to kill,” Gilroy said.


Among other questions asked by task force members was one from Carol Lee, who wondered why Travis County didn’t have staffers on the partnership that meets regularly to monitor and control hydrilla. While the county once participated they no longer do, Gilroy said, adding that she would check with the county about being involved.


Members of the task force, as well citizens who addressed a public meeting in October, rank hydrilla as among the highest-priority problems that need to be addressed on Lake Austin, the 20-mile portion of the Colorado River between Mansfield and Tom Miller dams.


The 17-member task force was created by Austin City Council earlier this year to develop recommendations to improve the lake after the city began hearing increasing complaints from the public about not only hydrilla but shoreline erosion, degradation of water quality, inadequate supervision and construction of unpermitted structures, among other issues. The task force is scheduled to report its recommendations to City Council in June 2013.

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