Lives of a River
Many small creatures have evolved in harmony with rivers.
By Wendee Holtcamp<
Wearing rubber waders to my hips, I’m smack dab in the middle of a riffle, trying to keep my balance against the knee-deep current of the San Marcos River. I plant one pole of a seine net ﬁrmly on the river bottom, as translucent green water gurgles over boulders and rocks that hide the river creatures we’re trying to ﬁnd. With me in the river are a trio
of Texas Parks and Wildlife Department aquatic biologists — Randy Moss, Kevin Mayes, and David Bowles — and my 7-year-old son, Sam.
Randy Moss, senior scientist with the River Studies Program of the Texas Parks and Wildlife Department, has a thick brown beard, an insightful way of describing things and a subtle sense of humor. “Kick the rocks as you walk downstream,” Moss tells Sam. “That will make the fish swim toward the net.” Sam obeys with wild abandon, his little legs doing their best to upturn rocks, and Moss follows behind him.
“Pick up the net!” Moss says, and Mayes and I swing up the two poles to create a sort of hammock. We peer in to see what little creatures we seined up. “Sunglasses!” Moss says as he removes the wiry frames missing one lens. Various creepy, crawly invertebrates scuttle over the white mesh, along with a half dozen small, wriggling fishes — darters, shiners, chub and sunfish. We place the creatures in a plastic bucket and try again. This time, we catch more wriggling fishes and scuttling invertebrates, some exotic Asian clams, and a piece of gray plastic — the missing lens.
“Now we have a full set of glasses,” Moss deadpans. We slosh through the water back to the riverbank, hauling our catch inside the folded-up seine.
To the casual observer a river might seem just a ribbon of water, maybe a place to throw a fishing line, or float down with your butt wedged through an inner tube. It’s easy to take for granted the watery wonderland beneath the surface, where fish, prawn, bug and mussel interact in an intricate web. Freshwater mussels with names such as fatmucket, deertoe and pistolgrip siphon water pollutants from the sediment. Invertebrates carry on private lives in and about the underwater rocks, and minnows dart around seeking invertebrates to devour. Frogs lay eggs at the stream’s edge, bridging the gap between terrestrial and aquatic worlds.
Rivers boast as complex a geography as any land they run through, with deep, fast-flowing regions known as runs, slow flowing, deep pools and rocky riffle habitats. Many aquatic organisms breed and feed in the riffles, like the spot we are seining. As water flows over rocks, it draws oxygen into the river. Nooks and crannies in the rocks provide habitat and breeding substrate for riverine creatures and their eggs and larvae, particularly invertebrates that are, in turn, food for fish, frogs, salamanders, turtles, crayfish and even giant river prawn.
But build one large dam and several small, conveniently placed bridges across riffles, pump water out of the aquifer that feeds the spring, straighten out the natural river curves, introduce exotic species, and you’ve got a riverine feng shui disaster. Feng shui is the ancient Chinese art of enhancing one’s living environment by improving harmony and energy flow. But nature got rivers right the first time, and now it’s up to us to repair any damage already done.
“People see water in a river and they think it’s OK,” Moss says. “Because of rainfall, we’ll always have streams and rivers with flowing water, but the question is whether they’ll harbor the biological life they used to.”
The sunglasses testify that, despite the San Marcos’ relatively healthy aquatic ecosystem, no river system remains unaffected by the state’s burgeoning population. Texas population is predicted to nearly double to 40 million people by 2050, and as the population grows, demands on rivers and their underlying aquifers will only increase. Citizens need drinking water. Private business and economic interests want their share. Recreationists desire healthy streams for fishing and boating, and fish and wildlife require clean, abundant river water to survive and thrive.
The TPWD river studies staff recently studied how altered flows at the San Marcos springs, the second largest spring in Texas, might affect the river ecosystem. They found that maintaining normal, less-than-normal and above-normal spring flows allows the river to cleanse itself — to flood its banks and to shrink back. These natural fluctuations flush the river, transport sediment and maintain the river channel. The spring river system must be maintained in its naturally dynamic state for the creatures that have evolved with it to survive. If excessive aquifer pumping alters the natural duration and patterns of spring flow, the river system changes and the river’s spring flora and fauna inevitably suffer.
Convincing the average citizen that spring flow dynamics, or the wild creatures that depend on them, are worth protecting often proves to be more difficult than studying them. “It’s a tough sell for us to convince the public that they should care,” Moss says. “People often have an attitude of, ‘Why should I care that we’re going to lose a minnow?’”
Sam is ecstatic over the minnows we caught. He removes fish from the net and plops them into the bucket. Kevin Mayes, a TPWD aquatic biologist, identifies the species. He shows us the various types of minnows — blacktail and red shiners, the torpedo-shaped speckled chub, as well as his favorite, a male stoneroller, a smallish fish with bumpy nuptial tubercles on its forehead. “They have hard heads,” Mayes explains. “They use them to push stones around to make a nest. They also use them in mating rituals. They rub their tubercles on the female’s belly and genitals.”
Mayes identifies the dusky and orange-throat darters we’ve netted. “It’s a patriotic fish,” I say, since its colors look red, white and blue to me. Mayes assures me the orangethroat’s colors are actually orange and green, not red and blue. He also explains that all darters have reduced air bladders so they can feed on river bottoms.
“Notice the males are more attractive than the females,” Moss pipes in, contrasting the drab females to the brightly colored males, “just like in humans. Really, the males are more desperate,” he says with a chuckle, explaining that many fish species are sexually dimorphic, with males more brightly colored to attract females.
Darters, chub, shiners and stonerollers are truly river species, depending on flowing water, riffles and the natural structure of rivers to survive. “In an average river, about half the fish can do okay in a pool or lake, and half need flow,” Moss explains. These river-adapted species evolved so closely with natural river conditions that changes inevitably lead to their decline.
“Blue suckers are an extreme example in terms of needing flow,” Moss says. These large fish have a hydrodynamic shape like a jet plane, with fins like wings. Their strong musculature allows them to swim against the current. Blue suckers reside throughout the Mississippi River drainage in the eastern United States, and in Texas reside in the Colorado, Red, and Rio Grande Rivers. Mayes says that there are a few historic records of blue suckers in the San Marcos, Brazos, Nueces, Sabine and Neches Rivers, but TPWD River Studies biologists have never caught one in these rivers.
“It’s easy to explain why it’s declining throughout its range,” Moss says. “It used to be so common that it was used for food, and now most places it occurs it is a state endangered species or species of concern.” Blue sucker eggs stick on the rocks in riffle habitat, and their population decline often follows the disappearance of riffle habitat, as well as changed flow regimes caused by dams. Riffles face three simultaneous threats: damming of rivers inundates them, reduced water flow exposes them and they often become convenient spots to build bridges across rivers.
As we learn about river fish, David Bowles scours rocks for more invertebrates. He scoops up river water containing invertebrates into a white porcelain pan. After a few minutes, he brings them over to the bank and dumps them into the bucket.
Sam looks inside. “They are playing football! They are all tackling each other,” he says. The mayfly larvae and the centipede-like hellgrammites settle down on the bottom. Bowles shows us the mayfly larva’s aerodynamically rounded head, and raptorial front legs, adaptations for clinging onto rocks in fast flowing water. We also catch other bottom-dwelling creatures: the naucorid, with a flattened, penny-like body and piercing, sucking mouthparts and the tiny, caseless caddisfly larvae that attach to rocks and spin silk catch-nets to retrieve even tinier bits of food.
Bowles and other aquatic biologists measure invertebrate biodiversity as a quick way to assess a river’s health. Some species, like mayfly larvae, are very sensitive to pollutants and low oxygen, so they won’t be present if water quality is poor. Riffle regions often have the highest invertebrate biodiversity, while other river regions aren’t so productive. He explains how small dams along a river can have a big impact on the river biota.
“Cape’s dam backs water up into a little lake filled with soft sediment,” Bowles says. “Hydrilla is the only thing that’s there.” Hydrilla is an alien plant that covers the surface of the impounded river region, preventing light from reaching the water below and choking out the native biota. The small impoundment causes a cascade of negative impacts. “These channel dams don’t have any purpose anymore,” Bowles says. “They were built for mill races in 1900s, and we don’t have mills anymore.” Bowles and others would like to see the old mill race dams removed to restore the San Marcos River to more natural conditions.
Dams, small and large, prevent migratory species from moving up- and downstream to spawning grounds. Dams in the Trinity, Angelina, Neches, San Jacinto and other East Texas rivers prevent endangered paddlefish from migrating upstream to spawning areas and are thought to have directly contributed to their decline. Likewise, here in the San Marcos, dams have likely led giant river prawn, or shrimp, into decline. River prawn are giant relatives of saltwater shrimp, have pinchers like lobsters, and live in freshwater rivers, but their eggs float downstream to coastal estuaries, where they develop and grow.
“If the eggs don’t reach a certain salinity by a certain time, they die,” Bowles explains. “They’ve estimated before all the dams it would take them four to five days to reach the estuary.” Now, eggs of the shrimp that live near the spring die because the dams slow their downstream journey. “The individuals closest to the estuary maintain the population because the larvae of the ones that live upstream can’t make it down to the estuary anymore.” When the young prawns reach a certain size, they migrate upstream, where they again face challenges getting past the dams.
Texas rivers and the creatures that depend on flowing water face myriad threats — from dams and other changes, to natural flow regimes, to exotic species to pollutants. “The problems with Texas water come down to two things: quantity and quality,” Bowles says. “Under these two broad categories are a myriad of problems that are often additive.” The question becomes: What water issue is most pressing for conserving aquatic biodiversity?
“If I had to single out one thing for [the] Edwards [plateau region], I would have to say water quantity,” Bowles stresses, “because if you have a mild pollutant, fauna may be able to hang on, but if you don’t have any water, nothing can tolerate that.”
The following weekend, I’m streamside to a true desert oasis, the clear blue waters of the spring-fed Independence Creek, which meanders eight braided miles through the Chihuahuan desert before spilling into the Pecos River. The feng shui of this near-pristine creek is preternaturally sublime. Mist rises from the 70-degree creek and the rising orb of the sun reflects gold and rose hues onto the mesas. Clark Hubbs, hands wizened from the years, sits on a stool hunched over three porcelain trays full of little fishes. A handful of people flurry about the nucleus he forms - setting out fish traps, retrieving them, testing water quality.
Officially, the octogenarian Hubbs is regents professor emeritus of Zoology at the University of Texas at Austin. To his students and colleagues, Hubbs is the godfather of Texas fishes. He’s collected fish from just about every stream in Texas and has published more than 300 scientific papers.
“Dump the water in that tray through this net,” he tells me. I pick up a tray and dump the water and the fishes through the green aquarium net he holds. He peers at the pile of squirming fish and after a few seconds, calls out “seven hundred five,” and dumps them into a bucket to be released back into the creek.
“You can tell how many fish are in there?” I ask, understanding why students call them his Rainman counts.
“I’m good at counting fish,” he says with a grin.
Hubbs is here to sample minnows and other river fishes near the spring’s headwaters and further downstream. Besides tallying total numbers, he identifies how many individuals of different species he finds at different locations. “I’m trying to find out which guys live in springs and which live in rivers,” Hubbs says.
Hubbs’ research comparing spring and downstream fish assemblages takes him regularly to the San Marcos River. Like the San Marcos, Independence Creek begins with a spring gushing 70-degree water from the earth and farther downstream, becomes less crystal-clear and with more variable temperatures — colder in the winter and warmer in the summer compared to the area near the spring. Certain fish species have evolutionary adaptations for surviving under a constant spring environment versus the more variable downstream region, and they face different challenges.
Six Texas fishes have gone extinct since he first started collecting fish with his father, the late ichthyologist Carl Hubbs, in the 1930s, and several other fish are now federally listed. “When spring flow declines, spring fishes lose part of their range,” Hubbs explains. “As many spring fishes are endangered, this can be important.”
Reduced flow is no case of “crying wolf.” Sixty-five of Texas’ 281 historically important springs stopped flowing altogether in the past hundred years, including two of the largest. The once raging Rio Grande has turned to a trickle in portions because of excessive water removal. Though water often seems a free, infinite resource, clearly it is not. Like fossil fuel, spring and river water are finite, limited resources that citizens and business interests can use up faster than rainfall naturally replenishes it.
When I ask Hubbs what he considers most important way to protect the fauna of Texas rivers in the next few decades, without hesitation he says, “Repeal that damn right-of-capture law.” The statewide right of capture law says that landowners can pump as much groundwater as they want. And it is the groundwater that feeds the springs.
Hubbs’ fleece sweatshirt is emblazoned with fish. I’m told he always wears some item of clothing with fish on it. When I ask if he likes to fish in the traditional sense, he answers, “Why catch four fish when you can catch 2,000?” You can’t escape the feeling there’s not much else he’d rather be doing than studying fish in the outdoors.
As I watch Hubbs and consider his deep love for fishes, I recollect that he was probably around my son’s age when he started collecting fish. Sam started when he was three, and his enthusiasm for wild things hasn’t waned, and I hope it never will. While the biologists and I sat around a table discussing the ups and downs of aquatic organisms in Texas rivers, Sam waits semi-patiently, periodically peppering the conversation with “I want to go catch fish!” and “Can we go out to the river now?”
It honors the passion of both old and young that we should protect, conserve, and restore the natural dynamics of our rivers — their natural feng shui, if you will — ensuring that the creatures that depend on them flourish well into the future. Doing this is not as as easy as hanging a wind chime to soften the hard edge of a dam, but in the end the fishes will thank us.