In the southeastern United States, if I were to mention kudzu or Chinese privet, these are tangible examples of invasive species from the plant world. The very name “invasive species” almost carries a negative connotation. By using the word invasive you immediately know it’s not a good thing. One example in the fish world that might fly under the radar of most anglers is the idea of bass as an invasive species. By definition, an invasive species is a species that is not native to a specific location and can spread causing damage to that ecosystem. Bass are one of the most sought-after game fish in the world, and that has led to a lot of movement between water bodies to create fishing opportunities that might not have previously existed. Unfortunately, unlike many other species, black bass have weak reproductive barriers. That means different species can interbreed and produce fertile offspring. The offspring (hybrids) can therefore mate and produce more hybrids. This is in contrast to most species where offspring are infertile, like with a mule. A female horse mated with a male donkey produces a mule, but due to chromosome number differences there are usually no successful cases of fertility. That’s not the case with bass, and this can have far-reaching consequences on an aquatic ecosystem. There are several prominent examples of this around the southeast.
One of the most well-known cases is the illegal introduction of Alabama Bass by anglers into the upper reservoirs of the Savannah River. Sometimes these fish are incorrectly called Spotted Bass, or Spots by anglers. They were described as a separate species by science in 2008, and are fundamentally and genetically distinct from Spotted Bass, although the look very similar. Alabama Bass are native to the Mobile Basin, but have been stocked purposely and accidentally all over the southeast. Anyways, back to the Savannah River, anglers in this area wanted to catch bigger fish than what was available with the native Bartram’s Bass (Micropterus), so they put some Alabama Bass into Lake Keowee in the mid-1980s. In just under a decade, Alabama Bass became the most commonly caught black bass species. This increasing frequency of Alabama Bass being caught was coupled with a decline in catch rates of the native Bartram’s Bass. By 1997, there were no genetically pure Bartram’s Bass found in Lake Keowee. It was unknown whether the correlation between the two was due to competition or some other reason. A team of researchers sampled the reservoir and examined the fish using genetics. The results showed that hybridization between the two was to blame, not competition, and that the introduced non-native Alabama Bass were hybridizing with the native Bartram’s Bass. A similar story played out in Lake Russell. Today, all major impoundments in the Savannah River system contain Alabama Bass. The migrating fish appear to be first generation (F1) hybrids that preferentially mate with pure Bartram’s Bass. More recent studies in the early-2000s showed that the only areas containing pure Bartram’s Bass are the river and tributary streams. By 2008, five out of eight tributaries sampled contained Alabama X Bartram’s Bass hybrids.
You might be asking yourself, what does it matter? Why is this a bad thing? The population of Bartram’s Bass found in the Savannah River system have been shown to be an endemic population of the Redeye Bass Complex that is genetically and morphologically unique. That means it is found in the Savannah River and nowhere else in the world. The hybridization of this unique and special fish with invasive Alabama Bass is causing a loss of a species right before our eyes, and all we can do is watch. Loss of a species is one outcome, especially with these endemic bass populations like Redeye Bass, Suwanne Bass, Shoal Bass, Guadalupe Bass, and Choctaw Bass. I doubt the anglers that stocked these fish had any idea what the result of their actions would be, or maybe they did, but didn’t care. The point isn’t to point blame, but to provide an example of how important it is to not put fish where they don’t belong. As if the situation in the Savannah River couldn’t get any worse, in 2007, anglers also bragged about introducing Smallmouth Bass to the Savannah River at the Augusta shoals area. In just a few years, 30% of fish sampled in the area were hybrids between Smallmouth Bass and Bartram’s Bass. This has only exacerbated the loss of Bartram’s Bass by hybridization with non-native Alabama Bass introduced illegally by anglers.
I wish this blunder was confined to only one major river system in the south, but an almost identical situation is playing out in the Chattahoochee River. Alabama Bass were illegally introduced by anglers into Lake Hartwell in the 1980s. Since that stocking, Alabama Bass have spread throughout and hybridized with native Shoal Bass and Chattahoochee Bass. This hybridization has spread to the point where both of these populations are in peril and have been labeled by Georgia’s Department of Natural Resources as Species of Special Concern. A lot of research is going into understanding where pure populations of Shoal Bass and Chattahoochee Bass exist so that they can be protected from the migration and subsequent hybridization with non-native Alabama Bass.
Hybridization in the black bass is very important. It has probably played a large role in speciation of that genus, but it also is creating huge issues for fisheries managers and state agencies due to illegal introductions. This should necessitate that we anglers understand the consequences of putting fish where they don’t belong, and also that we encourage fellow anglers to stop moving fish around. The genes of the larger Alabama Bass has also led to several state record Redeye Bass being misidentified. Images of these clearly show they are Alabama Bass X Redeye Bass hybrids. Some states are starting to incorporate genetic testing to verify potential state records for this very reason. While state records and trophy designations might sound like semantics, I hope this article shows you there are far greater consequences of invasive bass than misidentification.