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August 28, 2008

DNR biologists continue to study redeye bass

One of South Carolina's native bass, the redeye, is in decline, but not for the reasons one might suspect.  It's not overfishing or loss of habitat that has biologists concerned about this fish's status, but rather its interaction with a closely related species, Alabama spotted bass.

Alabama spotted bass were introduced, presumably by anglers, into Lake Keowee in the mid-1980s. This unauthorized introduction resulted in the growth of a significant spotted bass fishery there, which coincided with a dramatic decrease in abundance of native redeye bass. There was a similar introduction in Lake Richard B. Russell. The Alabama spotted bass has spread throughout the upper Savannah system of reservoirs, and is now present in Lakes Jocassee, Keowee, Hartwell and Russell. By the early 1990s fisheries biologists were seeing physical characteristics of both species in single specimens, and redeye bass from Lake Keowee were becoming difficult to identify. Hybridization between native redeye bass and the introduced Alabama spotted bass was suspected, and later confirmed through DNA analysis.

The redeye bass is one of the black bass, a group of closely related species that includes the more widely known largemouth, smallmouth and spotted bass. The redeye and largemouth bass are the only two black bass native to South Carolina waters. The redeye bass is one of the more rare black basses. In South Carolina, it is native only to the Savannah River drainage, comprising a natural resource that is unique to the state. Studies have shown Savannah drainage redeye to be distinctive both physically and genetically from redeye in other drainages within the species' range. Redeye bass prefer cool flowing mountain foothill and piedmont streams, but have also thrived in the upper Savannah lakes. The world record redeye bass weighed 5 pounds, 2.5 ounces, and was caught by a South Carolina angler on Lake Jocassee.

The S.C. Department of Natural Resources (DNR) has partnered with Duke Energy and University of South Carolina in the study of redeye bass, and has been awarded a federal grant to fully evaluate the impact of hybridization on redeye bass throughout the Savannah drainage. Beginning in 2004, tissues from about 1,300 bass were collected for genetic analysis. Fish were evaluated from Lakes Jocassee, Keowee, Hartwell and Russell, as well as from eleven stream redeye bass populations throughout the drainage.

DNR monitors stocks of freshwater fish throughout the state and engages in public outreach efforts to educate anglers on the importance of returning fish only to those reservoirs from which they came. This was highlighted during the Aug. 14-17 Forrest L. Woods Tournament when tournament officials paid special attention to maintain separate hauling trucks for those fish caught in Lake Murray and Lake Monticello.  DNR biologist Jean Leitner said, "The movement of fish, or of any aquatic plant or animal, from one water body to another has the potential to do severe damage. What we have found in our redeye bass populations is a perfect example of that."

While nine of 11 stream populations were free of hybrids, what has been found in the lakes is much more negative. Pure redeye bass have become extremely rare in Lakes Keowee and Russell, where Alabama spotted bass were introduced and initially 'took off' in the drainage. The non-native Alabama spotted bass made up 33 percent and 21 percent of the fish analyzed from Lakes Keowee and Russell, respectively, while redeye bass appear to have been almost completely displaced.  Less than 1 percent of fish collected from Keowee, and only 5 percent collected from Russell could be identified as redeye bass. 

Redeye bass did comprise 44 percent and 32 percent of fish analyzed from lakes Jocassee and Hartwell, and pure Alabama spotted bass were rare in those two populations. But hybrids made up 24-32 percent of fish caught from all four lakes.  The majority of those hybrids were the result of redeye bass x Alabama spotted bass crosses. A small number of hybrids between largemouth bass and Alabama spotted bass were collected as well.  

"The proportions of pure redeye and Alabama spotted bass found in the four lakes studied correspond well with the introductions of spotted bass into Lakes Keowee and later Russell," said Leitner. "Further, the displacement of redeye bass in favor of Alabama spotted bass in Lakes Keowee and Russell indicates that hybrids between the two species are selectively backcrossing with redeye. If this is the case, we would expect the proportion of redeye bass in Lakes Jocassee and Hartwell to decline with each successive generation. Over time, they would approach those seen in Lakes Keowee and Russell. Certainly the ability of native redeye bass to persist in these reservoirs is in question."

An equally negative, but more recent development in the status of the native redeye bass of the Savannah drainage is the sudden appearance of non native smallmouth bass in the area of the Savannah River known as Augusta Shoals. A push to stock smallmouth in that area of the Savannah has been resisted by both the Georgia and South Carolina DNR's because of the threat it would pose to redeye bass. However, over the last year anglers have reported catches of smallmouth bass in the shoals. DNR followed up those reports with collections of fish last fall, and confirmed the presence of smallmouth bass as well as hybrids in a population that yielded only pure redeye bass three years earlier.

Leitner said this emphasizes how damaging the indiscriminate movement of fish can be. "Hybridization in those major redeye populations represents a huge loss for one our native natural resources," she said. "We were glad to still find pure redeye in many of the smaller streams surveyed.  Protection of those habitats and the fish in them will likely prove vital to the future of redeye bass in the Savannah drainage. "

Contact DNR biologist Jean Leitner via e-mail at LeitnerJ@dnr.sc.gov for more information on redeye bass in South Carolina. Find out more about freshwater fishing rules and regulations.

DNR protects and manages South Carolina's natural resources by making wise and balanced decisions for the benefit of the state's natural resources and its people.

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