BOB MAINDELLE: Invasive plant spreading rapidly in Stillhouse Hollow Lake | outdoor sports

Over the past few months I have heard a number of my clients and others with more than a passing interest in our local reservoirs comment on the apparent growth of vegetation at Stillhouse Hollow Lake.

Some have speculated that the growth is algae; others thought what they were witnessing was the revelation of the bottom of the lake due to low water levels. Neither is true.

The fast-spreading form of vegetation is an invasive plant species called hydrilla.

Although there have been ups and downs in the amount of hydrilla found at Stillhouse Hollow since its inception in the 1990s, this year its spread and coverage reached an all-time high.

In years past, only the lower two-thirds of the reservoir contained the plant, but this year the hydrilla has spread to the upper third of the reservoir, bringing it into the mouth of the Lampasas River and into the cove formed where Trimmier Creek enters the reservoir.

There are a few pros and many cons associated with growing hydrilla.

In the short term, hydrilla provides shelter for cover-loving and ambush-feeding fish species such as largemouth bass and pumpkinseed. However, too many good things are possible.

According to a 2016 article published by Cornell Cooperative Extension of Cornell University, “Although hydrilla can provide habitat for fish, it disrupts the predator-prey relationships of some fish. Some predatory fish (such as sunfish and bass ) attack their prey by ambushing them and benefit from the additional cover provided by the hydrilla. However, in the long term, this can lead to an overall decline in the fish population, and even fish that prefer cover cannot hunt when the hydrilla becomes too dense.

A popular saying among largemouth bass anglers advises, “Find the grass; you will find the bass.

Sadly, hydrilla has grown so much in Stillhouse that entire coves are now completely inaccessible to boat anglers as tangled vegetation tangles the propellers of outboard motors and electric trolling motors, preventing access.

It has also become difficult for shore anglers to access the waters of the lake as the hydrilla has taken over a strip of shore water to at least 14 feet in depth in most places, thus preventing casting from the shore without tangling baits and lures. in the weeds.

Once bustling shore fishing areas like Cedar Gap Park and the unimproved access under the south end of the FM 3481 bridge, are now rarely used.

According to this same Cornell Cooperative Extension article, there are several reasons why hydrilla is doing so well compared to other forms of native vegetation. First, it can tolerate lower light conditions than most aquatic plant species, allowing it to start photosynthesis earlier in the morning, giving it an advantage.

Second, it spreads efficiently through tubers and spears. And finally, there are no native predators that eat hydrilla, and so their growth is unchecked.

The Cornell article states, “These adaptations allow hydrilla to outcompete other plants for growing space. In fact, hydrilla is so successful that it can double its biomass every two weeks during the summer and can fill the entire water column up to 20 feet deep, creating a monoculture – a term used to describe areas dominated by a single species, as opposed to a regular ecosystem that contains many species. Monocultures can be harmful by limiting the ability of animals in the area to find food or habitat and by preventing the growth of native plants, thereby reducing biodiversity.

This same article highlights other negative impacts on fish, stating, “Hydrilla also harms fish as it depletes oxygen levels in the water. Hydrilla, like all plants, emits CO2 and uses oxygen at night (although the reverse is true during the day), which can bring oxygen levels to dangerously low levels for fish. Additionally, an increase in hydrilla can lead to an increase in nutrients released from the sediments which cause algal blooms, again depleting oxygen levels.

Birds can also be negatively affected by hydrilla. The Cornell article states that “bird populations are affected by declining fish populations and may also be affected by toxic blue-green algae growing on hydrilla leaves.”

I have previously observed that hydrilla has now severely smothered many of the slow tapering flats in the upper third of Stillhouse Hollow which serve as spawning grounds for the lake’s main forage fish, threadfin shad.

Although there are many approaches to slowing or reversing the spread of hydrilla, the three most common approaches include the use of chemical treatments (usually for “spot” treatment of smaller areas) and/or lowering the level of the reservoir below the extent of growth of the hydrilla. , and/or the introduction of barren grass carp, nickname of the Asian white grass carp.

According to the Texas Department of Parks and Wildlife Triploid Grass Carp Fact Sheet, triploid grass carp should be 10 to 12 inches long when stored, as small carp are susceptible to be eaten by other fish. To improve the efficiency of triploid grass carp, overabundant vegetation must first be reduced by overwintering, herbicide treatment, or lowering the water level to promote grazing during regrowth. The recommended stocking rate for triploid grass carp is five per acre if the water body has 50% vegetation cover or less, and 10 per acre if the vegetation cover is greater than 50%.

To be clear, I am not advocating for or against hydrilla control at this point, but my intention for writing this article is to identify what is growing in Stillhouse Hollow in order to clear up any confusion about it, and to point out that, contrary to popular belief, excessive hydrilla growth can have a negative impact on fish and fishing, even for cover-loving species like largemouth bass.

People concerned about hydrilla growth on Stillhouse and/or those looking for more information on this topic can contact the Waco Regional Office of the Texas Parks and Wildlife Department by phone at 254-666-5190.

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