Fish used to combat growing hydrilla problem
By KIMBERLY STAUFFER and BETH KUHLES
Copyright 2006 Houston Chronicle
The San Jacinto River Authority and Texas Parks and Wildlife officials decided to dump 13,800 grass carp into congested Lake Conroe to combat spreading hydrilla after a September survey showed rapid growth.
The fish are expected to be introduced into the lake sometime in the next month.
In July, hydrilla infested 739 acres of Lake Conroe. By September, the foreign plant had spread to 1,167 acres. Earl Chilton, aquatic habitat coordinator for Texas Parks and Wildlife, said the stocking rate is now 23.1 fish per acre, a marked increase from earlier this year when officials began treating the lake with five fish per acre. Officials began a conservative assault on hydrilla in March with 4,300 fish and now, factoring in a 30 percent annual mortality rate, Lake Conroe will have about 27,000 grass carp.
Montgomery County commissioners have joined the battle over hydrilla on Lake Conroe, urging officials to use whatever means necessary, including the maximum number of plant-eating fish — 30,000 — to preserve the lake.
Commissioners passed a resolution allowing the maximum number of fish allowable under the Hydrilla Management Plan previously approved by Texas Parks and Wildlife to be deposited in Lake Conroe.
Mike Bleier, president of the Lake Conroe Resident Association, said the organization is “extremely happy with the (lake officials’) decision.”
“With the announcement of 13,800 fish to be released, it doubles the amount of fish in the lake eating hydrilla, and that can only be a good thing,” he said.
Bleier said the lake weed has experienced 58 percent growth since July, which severely hinders lake usage and recreation.
“The lake appearance in certain places is not what it could be,” he said. “The use of motor craft in the lake is more difficult … because of increased number of acres (of hydrilla). It was a bit discouraging to see this growth. It’s encouraging that (Texas Parks and Wildlife) is at least acknowledging it.”
While not poisonous, the plant grows from buried bulbs in the lake bottom to the surface, developing into dense mats that prevent homeowners and tourists from swimming and using boats and jet skis.
Plant growth rate
The high growth rate is attributable to the lower water levels in the 21,000-acre man-made lake, with the combination of clear, shallow water and penetrating sunlight and runoff from local golf courses, residences and businesses contributing abundant nutrients.
Chilton said Texas Parks and Wildlife officials will conduct three surveys each year to measure hydrilla growth to determine if any fish need to be added to the lake. Surveys are planned for May, July and September.
“We’ll wait until the survey next spring to determine whether we need more fish and determine how well the natives (plants) are growing. If the hydrilla is growing at a significant rate earlier in the year, we may go ahead and do a March or April survey. It just depends on how the lake is doing.”
Like Lake Austin, which has endured similar hydrilla infestations, Chilton said battling the weed could take up to two years using a conservative approach to avoid overstocking the lake, a mistake officials made in the early 1980s that ultimately destroyed Lake Conroe’s native vegetation.
In the late 1970s, Lake Conroe became infested with the Southeast Asian plant, which eventually covered 45 percent of the water. Officials treated the outbreak with herbicides until the plant consumed about 7,500 acres just three years after the initial expansion.
In reaction, lake officials dumped almost 300,000 grass carp in Lake Conroe. The fish, also known as white amur, eliminated the foreign plant, but the severe overstocking decimated the native vegetation when the hydrilla, the grass carp’s favored food, disappeared.
Bleier said he believes officials have had to change their moderate stance on fighting hydrilla because of unexpectedly fast growth.
“I think the hydrilla unfortunately is growing faster than they had hoped for,” he said. “Once they measured that growth, they responded accordingly with an adequate number of fish. There were signs of hydrilla growth and expansion (two months ago), so I think their conservative approach couldn’t be maintained any longer because of rapid growth being seen out our windows every day.”
Chilton said the warm weather months of July, August and September contributed to the fast hydrilla growth, but the onset of cooling winter temperatures should slow the weed.
“We believe it’s probably slowed down its growth rate,” he said. “You should expect some kind of dieback in winter depending on the weather. It’s still increasing, but at a significantly slower rate than before we put the grass carp in.”
Maintaining lake’s health
Lake officials will continue to administer herbicides in conjunction with the plant-eating fish, Kellum said.
“It’s an ongoing maintenance situation,” he said. “We’re using herbicides to maintain the health of the lake.”
Chilton said he hopes the recent measures to impede hydrilla expansion quells Lake Conroe residents’ concerns with officials’ reactionary tactics.
“It’s hard to tell. I imagine some of the residents may be pleased and willing to wait until next summer to see how this number of fish is doing,” he said. “Other ones may be some who are still upset and want more fish. It’s difficult.”
Lake Conroe Association members campaigned for 30,000 fish while lake officials continued a conservative program to treat the lake. The association held a fundraiser to raise money for grass carp and hydrilla control. Residents and businesses contributed $191,000 to the campaign, and the San Jacinto River Authority agreed to pay half the cost for purchasing the fish.
“Getting 90 percent of our goal in the first year is a proactive approach and we’re pleased (Texas Parks and Wildlife) made that decision,” he said. “The winter is going to bring cooler temperatures, which will slow hydrilla growth, and we’ll have 27,000 fish in the lake to start eating away.”