Breeding with their introduced relatives threatens to drive Guadalupe bass to extinction.
By Wendee Holtcamp
We arrive at the Blanco River in the early morning hours. A half-dozen pecan trees, stark in their winter nakedness, stand silhouetted along its shoreline, grapevines forming a tangled mass in their limbs. “Bring a fishing pole, tackle, cold/wet weather clothes, old pair of tennis shoes, water, and maybe some snacks,” Texas State University Biology Professor Tim Bonner told me a few days before our excursion. He’s here to show me how he and his students “sample” Guadalupe bass — with rod and reel, mind you — this being one of three sites where Bonner and his graduate students conducted a study of the rare fish. A day in the life of a fish biologist — tough work indeed.
Bonner puts a salt-and-pepper grub on my fishing line. “I’m not very good at this,” I admit. I’m not an angling aficionado, just someone willing to don a pair of chest waders and who knows how to cast a line and look halfway like I know what I’m doing. We step into the Blanco’s clear blue water, casting near the river’s edge as we talk. We’ll catch whatever our lures attract — Guadalupe, smallmouth and Florida largemouth bass all live in the stream reach, the former being native and the latter two introduced.
Like trout fishing in the north country, to fish for Guadalupe bass is not about catching a stringer of large bass so much as it is about the experience of spending a day outdoors on a beautiful Hill Country stream casting for these agile, river-adapted fish. In all of the world, these Texas endemics live only on Texas’ Edwards Plateau.
Narrow and sleek, Guadalupe bass evolved for life in Hill Country streams. They diverged from their closest relative about 6 million years ago, and became adapted to the flowing water and temperature variations typical of a river — as opposed to largemouth bass which evolved for life at the more stable freshwater spring headwaters.
Numbers of Guadalupe bass have dropped precipitously over the past century. The fish declined initially because dams built on nearly all of the fishes’ native river drainages — the San Antonio, Guadalupe, Colorado and Brazos — permanently altered their riverine habitat. Dams not only reduce a river’s rate of flowing water, they also alter stream dynamics — the natural repeating pattern of pool, riffle, run. But about 15 years ago, biologists recognized a new and different threat: Guadalupe bass had started freely interbreeding with their cousins — introduced smallmouth bass.
Starting in 1974, TPWD stocked smallmouth bass as a sportfish in several Hill Country streams to enhance statewide angling opportunities. Different species are not supposed to interbreed, or so the ancient wisdom goes. According to the biological species concept, first coined in the 1940s by famed biologist Ernst Mayr, species were defined as “groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups.” In other words, their very inability to interbreed and produce fertile offspring with closely related species distinguished species from one another. The classic example is that of horse and donkey: while they can mate and bear offspring — a mule — they remain different species since mules are sterile. Until relatively recently, biologists didn’t really think of different species as capable of successfully interbreeding — it defied the very way biologists defined species.
Unfortunately, nature has proven messier than that, and biologists find themselves in the midst of a complete revolution in thought about how to define species. Instead of one popular species concept, dozens now exist, respectively popular among zoologists, botanists, and those who study microorganisms like bacteria or protozoa which defy most rules known to higher organisms. Biologists now accept that hybridization between clearly separate species occurs more frequently than previously believed but still can’t predict when any two given species might interbreed in nature.
One might think species would interbreed most easily with their closest relatives, but such species usually have evolved what are known as “reproductive isolating barriers” that prevent interbreeding, such as differences in mating behavior, breeding season, or incompatibilities between egg and sperm. Less closely related species — “cousins” — that have been geographically isolated from one another often have not evolved such barriers.
When biologists move species around, like they do when introducing smallmouth bass into a stream with Guadalupe bass, the two species do not have strong barriers to prevent inter-species reproduction. This little fact of biology can cause major conservation problems.
Once biologists realized, in the early 1980s, that smallmouths were hybridizing with native Guadalupe bass, the Texas Parks and Wildlife Department moved quickly to figure out the extent of the problem. Biologists sampled — by rod and reel — every stream where Guadalupe bass were native, including the Blanco. They used genetic techniques to distinguish pure Guadalupe bass from hybrids, since hybrids will carry genes characteristic of both species. “We found we have a horrible problem throughout the range,” says Gary Garrett, TPWD biologist, who led the study. “There were only a few pure populations left.”
The Guadalupe bass situation could have escalated into a serious conservation crisis. “When we first started wrestling with this issue, we realized its security was threatened enough that it could be a listed species,” explains Garrett. “There were some complications, such as that it’s a sportfish, plus it’s difficult to tell from large and smallmouth bass. We would have an enforcement nightmare.”
The solution they settled on was raising oodles of pure Guadalupe bass in tanks, and releasing them into the wild — something that can’t be done with, say, mammals. Over the next couple of years, TPWD raised certifiably pure Guadalupe bass at the Heart of the Hills fish hatchery in Ingram. Beginning in 1992, they stocked tens of thousands of fingerlings into two streams, the Blanco River and Johnson Creek, one of the Guadalupe River’s three major tributaries. “The goal was to simply overwhelm the hybrid population, and drive the hybrid proportion down,” explains Garrett. TPWD also stopped stocking smallmouth bass in most Hill Country streams by 1990.
After a couple of years, because of limited resources, TPWD decided to put all their fingerlings in one basket, so to speak, and to focus exclusively on Johnson Creek. Yet 80,000 Guadalupe bass were stocked into the Blanco during 1994 and 1995. It was not until 2005 that Professor Tim Bonner and his student Brad Littrell set out to determine whether the Blanco stocking program had succeeded in any capacity despite its short duration, or whether the Guadalupe bass had vanished, the pure individuals being driven to extinction in the river by interbreeding with their smallmouth cousins.
As Bonner and I proceed to fish, er, sample in the beautiful light of early morning, he explains what their study found. “Brad’s study is showing a huge red flag. Something is not right,” says Bonner. “Our research shows that pure Guadalupes are gone in the Blanco.” Although Blanco fish may resemble Guadalupe bass, essentially what remains in the Blanco are fish whose genetics show that their parents or grandparents some generation past were smallmouths. To add insult to injury, Bonner’s study found evidence that some Guadalupe bass — or their hybrids — had also interbred with largemouth bass.
I ask if he thinks the rare fish should become a state or federally listed species, but echoing Garrett’s sentiment, Bonner says, “Listing is not the way I think it should go.” Rather he believes that stocking plus increasing the popularity of the fish among anglers in Texas and even nationwide will draw attention to the species, which will help bring in funds for research and conservation.
As biologists debated how to reverse the fish’s downward spiral, third grade children at Decatur Intermediate School found out Texas didn’t have a state fish, and contacted Garrett. “I said, ‘Man I’ve got the perfect fish for you.’” The school kids and TPWD got the Texas Legislature to officially dub Guadalupe bass the state fish in 1989. “It helped us get more of a high profile.”
If the Blanco’s situation were mirrored on Johnson Creek, the Guadalupe bass may well have gone the way of the dodo. Fortunately for the fish, Johnson Creek has finally begun to see success — the recovery of pure Guadalupe and a reduction in the proportion of hybrids. “In the first few years, we could see a reduction, but it was not very rapid,” says Garrett. The first years of stocking lowered the percentage of hybrids in Johnson Creek to 15-20 percent, but the level within the Guadalupe River rose to 85 percent; it appeared that the hybrids were simply being pushed from the tributary into the bigger river. After 12 years of continuous stocking, the proportion of hybrids has now fallen not just in Johnson Creek but also in the Guadalupe — to around 30 percent. Hybrids are not gone, and interbreeding likely still occurs, but Guadalupe bass are starting to hold their own.
Two refuge populations of pure Guadalupe exist, completely free of hybrids because smallmouth bass were never stocked there. Ironically the refuge populations exist in streams where Guadalupes never lived historically: the Nueces and one of its tributaries, the Sabinal. Someone stocked the fish there back in the 1970s. “These days we don’t like to introduce species into new habitats but it was kind of fortunate that they did because we have a pure population of Guadalupe bass.”
I cast my line toward a large rock in the center of the Blanco, and immediately feel a bite. I glance at Bonner, who nods and talks me through reeling the fish in. The line tugs and I think it’s going to break, but I reel in a nice-sized bass. Alas, it’s a smallmouth. We walk ashore and see what others have caught. We weigh the fish; amid five anglers, I somehow end up with the largest catch. “I think she may be better than she let on,” laughs Bonner.
The fish show a remarkable diversity of form; several definitely resemble Guadalupe bass, and without the genetic studies, most would never know the difference. Unfortunately, hybridization and the subsequent introgression of genes changes more than just their look — it can weaken behavior and alter other adaptations that took millions of years to evolve. Any such changes typically reduce the species’ ability to thrive in fast-flowing rivers. Genetic alterations in breeding behavior can lead to greater chances of more hybridization, further threatening the species.
Bonner’s study confirms that Guadalupe bass recovery requires a long-term commitment. It won’t suffice to stock fingerlings for a couple of years and hope the species will recover. Rather, the year-in, year-out stocking of thousands of fish — as on Johnson Creek — appears to be their only hope.
“You’ve seen the worst end of it,” Garrett tells me. “Hopefully, what we’ve done over here will be the other end of resolving that.” With the success seen on Johnson Creek, TPWD plans to expand their project to the Guadalupe’s other two tributaries this year — the north and south fork. Just as the United States reversed the decline of America’s national bird, the bald eagle, Texas biologists hope to save the state fish of Texas with a patient and persistent long-term approach. “We’re going to stock a quarter million fish per year,” says Garrett, “We’re going to fix this one river system at a time.”