Flooding brings changes to pond fisheries
Water’s quality as the universal solvent, able to dissolve more substances than any other liquid on the planet, manifested that power in stunning, life-changing ways when unprecedented amounts of it fell on a huge swath of Texas’ coastal plain three weeks ago.
That water — as much as 27 trillion gallons, according to some calculations — swamped waterways and swept across the landscape in a week-long flood of almost biblical magnitude. As befits its universal solvent character, that water transformed in some way everything it contacted, most significantly the lives, futures and fortunes of millions of Texans.
It also changed the natural world, including the aquatic ecosystems it conjoined.
“Every single body of water those floods touched changed because of it,” Bob Lusk said. “Some will be changed more than others. And how they changed is a question that could take a while to answer. But all of them changed in some way. Bet on it.”
Lusk would know. The dynamics of freshwater fisheries — fish, other aquatic creatures, aquatic vegetation and the liquid in which they live —are his profession. A fisheries biologist who has practiced his calling for almost four decades, building a business — Pond Boss and Bob Lusk Outdoors — that specializes in designing and building private ponds and lakes, and developing and managing high-quality fisheries in those and other private waters, Lusk has deep experience and understanding of those topics.
The native Texan has clients around the nation and manages or consults on some of the most prestigious private waters in the country. He knows freshwater ecosystems. Time will tell
What Lusk saw as those trillions of gallons of water poured from the sky and devastated the lives of so many people horrified him. But he also knew that the flooding stood to have dramatic effects on the aquatic systems that are essential parts of so many Texans’ quality of life.
“There hasn’t been anything on this scale,” Lusk said of the rainfall and the resulting flood that impacted so many waters. “It’s going to be interesting to see how this plays out.”
Lusk has some ideas how it will or could play out based on his knowledge and experience.
All that water flowing across the landscape inundated thousands — perhaps tens of thousands — of farm ponds, stock tanks and small lakes on private property. That is not an exaggeration. Texas holds more private pond/tanks/lakes than any other state — about 1.2 million of the 4 million to 6 million such private waters in the nation, most of them ranging in size from a quarter-acre to 100 acres or more. The region hit hardest by recent flooding is pocked with thousands of those waters.
“All of those ponds will see some impact,” Lusk said.
And that will directly affect the fish, plants and other aquatic life in them, the wildlife such as waterfowl that depend up these waters and, significantly, the landowners and people who value those ponds for the recreation and environmental services they provide.
The ponds that weren’t wholly overwhelmed by floodwaters certainly saw massive inflows of runoff. That runoff brought a considerable load of organic (and some inorganic) material into the pond, some of it dissolved and suspended in the “universal solvent” and some deposited whole.
That dissolved material — animal waste, fertilizer, minerals leached from soil or rock, minuscule bits of detritus, etc. — suspended in the water and the large organic material settling on bottom or floating on the surface are immediately attacked by bacteria. Those bacteria gorge on the new surfeit of forage, exploding in number.
Different bacteria thrive in different waters, depending on what is carried into the water, Lusk said.
This starts a chain reaction that continues changes in the chemistry of the water that began with the slug of “new” water that poured into the pond — life in the food chain. Those changes can include altering of the acidity or alkalinity of the water (pH value), turbidity, nutrients and other characteristics that can determine which plants and aquatic life thrive and which struggle.
“You can have changes that benefit fish such as bass or changes that benefit other fish that may not be as desirable,” Lusk said. “With a boost in nutrients, you can see a boost in productivity. But it may not be the productivity of something you want.”
Those changes to a pond and its fishery will manifest over time. One, thankfully uncommon, can occur quite quickly in flooding events: fish killed by fire ants.
When heavy rains flood lands in a pond’s watershed, the runoff can bring with it large, floating mats of imported red fire ants. The fire ants, flushed from their nests, congregate in large masses that can contain thousands of the invasive, venomous pests.
These roiling masses of live fire ants can be carried into ponds or other waters. Fish species that regularly target insects can see the mass of ants as a serendipitous buffet and gorge on the helpless ants.
This can prove fatal. Fish ingesting large quantities of fire ants can die from the toxic effects of the formic acid in the venom that fire ants possess. Fire ants wreak havoc
Lusk has seen a pond where scores of dead bluegills, their bellies distended from gorging on floating fire-ant masses, floating in the wake of a flood. And fish in isolated ponds and lakes are not the only ones at risk. After heavy rains and flooding in central Texas in 1998 flushed rafts of fire ants into the Guadalupe River below Canyon Lake, more than 2,000 freshwater trout and hundreds of other fish in that section of the river died from preying on the toxic insects.
“It’s rare, but it certainly does happen,” Lusk said of such incidents.
Ponds and lakes near rivers and streams or other natural waterways face other problems.
“Those ponds and lakes that were inundated with floodwater from rising rivers are going to see changes in their fisheries,” he said.
Those ponds almost certainly lost this year’s production of young fish. Those small, young-ofthe-year fish — largemouth bass, sunfish and crappie — concentrate in pond/lake shallows, where aquatic vegetation and the shallow water provides some degree of refuge from predation. When flooding from nearby rivers swept over these areas, raising water levels, the young fish moved to find their preferred shallow-water habitat. They were either swept away by current or ended up stranded when water levels fell.
“Those ponds lost this year’s crop,” Lusk said.
But the ponds gained something, too.
“There’s going to be a measurable exchange of fish,” he said.
With river and ponds now connected, fish from both waters will take advantage of their expanded world to relocate — some swimming to new areas on their own and others carried by the current.
Most adult fish in ponds and lakes won’t leave. They are homebodies, with their behavior and conditioning leading them to hunker down in a place that provides cover and forage and wait.
“In a 50-acre lake, you’ll have bass that will never leave a three-acre cove their entire life,” he said. “They are conditioned to stay there because the habitat offers everything they need.” Some fish unwelcome
But that doesn’t apply to all fish. Some pond fish will “escape” during a flood event. But others will find their way to what was a closed system.
“You’re going to see new fish show up in ponds,” Lusk said.
And that is not necessarily a good thing.
“A lot of the fish that move out of rivers and end up in ponds during floods are carp, buffalo, gar,“he said.
Those species often are not the ones pond owners want in their waters, and those rough fish compete with more desirable species for limited resources.
Smaller species can create problems, too. Gizzard shad, a common fish in Texas rivers and large reservoirs, can find their way into ponds.
“It just takes a pair to create problems,” Lusk said of the large shad.
The gizzard shad population can explode in the confines of a newly nutrient-rich pond or lake, and the result of an overabundance of the shad can be disastrous.
“They can turn a pond into a mud hole,” he said, noting pond owners should closely monitor their pond’s fish population and water chemistry in the wake of flooding to head off any problems. Rivers? They will be fine. There will be physical changes — channels and sand bars will disappear, and new ones will appear. And the rivers could see a boost in productivity from increases in nutrients brought by runoff. But the demographics of the fisheries won’t be significantly altered.
That almost certainly will not be the case for many of the thousands of ponds, stock tanks and small lakes swamped by the record-setting rains and flooding associated with Hurricane Harvey.
“Nature’s incredibly resilient. Those systems, those ponds and lakes, will come back. But they’ll be different,” Lusk said. “How different is the question.” shannon.tompkins@chron.com twitter.com/chronoutdoors