The Satilla River is a blackwater system draining over 3,000 square miles of coastal plain habitat in Georgia. The tannic waters of this river are home to several species of catfish and panfish, and historically it has been one of the premier sunfish angling destinations in Georgia, particularly for redbreast sunfish (Lepomis auritus).
Several generations of anglers have continued to frequent the waters of the Satilla each spring and summer in search of Satilla gamefish, most notably the brightly-colored redbreast. Historically, these anglers likely served as the primary predator of redbreast and other panfish in the river. However, the unauthorized release of flathead catfish (Pylodictis olivaris) into the Satilla in the mid-1990s allowed for a new apex predator to be introduced into the river.
In 1996, the first confirmed captures of flatheads from the Satilla River were reported to the Georgia Department of Natural Resources (GA DNR). When observing these newly-discovered specimens, fisheries biologists noticed distinctive fin-clip markings mirroring fin-clip markings placed on fish released in the Altamaha River the previous year in 1995 (Bonvechio et al. 2009 & 2011). Consequently, it is likely the initial specimens captured in the Satilla were moved from the Altamaha River and released illegally into the Satilla.
As is often the case with the relocation of other non-native species, the introduction of the flathead catfish into the Satilla has created significant concern to both anglers and fisheries scientists alike. Flathead catfish are native to the Mississippi, Mobile and Rio Grande river drainages of the Gulf Coast (Jackson 1999), among other locales. Their popularity as a large gamefish capable of exceeding 100 pounds likely contributed to the expansion of their range, as anglers seeking new fishing opportunities illegally introduced them to new river systems, including the Altamaha and the Satilla. Since being introduced into the Satilla, flathead catfish have expanded throughout the river, having been documented as far downstream as the freshwater-saltwater wedge (brackish waters of Woodbine) and as far upstream as Waycross.
This expansion has not come without costs. Declines in both angler success and populations of redbreast sunfish, channel catfish and bullhead catfish began to be documented in the early 2000s. While factors such as fishing effort and water levels may also have contributed to these observations, the direct predation by flathead catfish has had devastating effects on these species.
As a result of these declines, fisheries scientists with the GA DNR began limited efforts to remove flatheads from the Satilla in the late 1990’s. By the early 2000’s, however, continued expansion of the flathead and the resulting increased impacts of its predation on native catfish and panfish resulted in a need to expand and increase removal efforts. Thus, in 2006, a crew within the GA DNR, Wildlife Resources Division, Waycross Fisheries office, was tasked with targeting flatheads on a full-time basis, thus resulting in the creation of the Flathead Removal Project (FRP).
In an effort to negate the impacts of flathead catfish on native fish populations, Wildlife Resources Division (WRD) staff began limited, but aggressive, removals of the species in the Satilla via electrofishing in 1996. Despite these removal efforts, the size and number of flathead catfish per hour of electrofishing continued to increase, and it was deemed that a more intensive removal effort with dedicated full-time staff was warranted.
In 2006, the Georgia legislature appropriated funding for three new positions within the WRD Waycross Fisheries office, thus resulting in the creation of the Flathead Removal Project (FRP). These full-time personnel were assigned the task of reducing flathead catfish population levels through direct removal while searching for additional long-term methods for controlling the population. In April 2007, crew with the newly established FRP began intensive removal efforts, removing over 4,000 flatheads from the Satilla that year. Despite this initial success, budgetary constraints resulted in a reduction of FRP staff to two full-time positions the following summer (2008). Nonetheless, thanks to the assistance of temporarily re-directed GA DNR staff, GA DNR Nongame Section grant funding and a host of volunteers, FRP efforts have continued.
Project Objectives and Results
Monitoring (Removal and Tagging)
A primary objective of the FRP is to monitor the flathead population to better know and understand the impacts of current management strategies. Monitoring efforts, such as tagging and sampling, are critical to the proper management of the flathead population and the recovery of the redbreast sunfish and other native fishes. Modeling studies in other states indicate that high exploitation or removal of flathead catfish may provide an avenue for the recovery of native fish populations. Consequently, the GA DNR has chosen an aggressive sampling approach utilizing electro-fishing gear to temporarily stun catfish and allow for selective removal. This equipment generates a low frequency electrical current in the water that temporarily stuns scale-less fish (including catfish) and allows GA DNR staff to use dip-nets to selectively capture only flatheads.
In an effort to obtain baseline information (such as movement, population size, total mortality, and fishing mortality) on the Satilla River flathead catfish population, GA DNR staff initiated tagging studies in early 2007. From March – April, 2007, 471 flathead catfish were caught using electro-fishing methods and tagged with a 3-inch long bright orange anchor tag. Similar efforts were repeated in March – May, 2008, with 96 flatheads caught and tagged. Results of the 2007 tagging efforts indicated that 53% of previously tagged fish were recaptured and removed, thus leading to an exploitation estimate (fishing mortality) of 53%. Additionally, conclusions drawn from analyzing otoliths (found in the inner ear of fish) removed from 484 flatheads included a calculated total annual mortality of 37 percent. Finally, depletion models completed by GA DNR biologists yielded an estimated 40-52 percent reduction in the flathead population. Based on these collective efforts, biologists concluded that the range of different mortality estimates calculated for the 2007 removal ranged from 37-53 percent.
Tagging studies were conducted again in 2008, and GA DNR staff found that 50% of the fish tagged that year were recaptured and removed from the river, thereby resulting in an exploitation estimate (fishing mortality) of 50 percent. With similar successful results being obtained in consecutive years (2007, 2008), no additional tagging has been conducted. However, the potential still exists that tagged fish may still be at-large, and thus anglers are still asked to report any fish caught with a tag to the GA DNR.
Since the implementation of the full-time FRP in April 2007, more than 59,000 individual flathead catfish have been removed from the river (as of July 2016). The size structure of the flathead population has been affected as a result of FRP efforts as well, with the average size fish removed dropping from 5.8 lb in 2007 to 2.2 lb in 2015. Biomass per effort has varied annually but has shown a similar trend, declining from 57.1 kg/hr in 2007 to 36.3 kg/hr in 2015. Interestingly, in addition to observing declines in both the average size and biomass of flatheads over the years, GA DNR staff have also noted several instances of female flatheads displaying gravid eggs at much smaller sizes than before. It is anticipated that such maturation at smaller sizes and younger ages is likely a compensatory mechanism resulting from high removal rates.
Given the results of tagging studies conducted in 2007/08 that yielded estimated fishing mortality rates of more than 50 percent each year and the continued trends of decline in average size and biomass of flatheads removed, maintenance control of flathead catfish in the Satilla River appears possible. This is further supported by past modeling estimates that have indicated significant declines in the size and numbers of Satilla River flathead catfish when fishing mortality rates are higher than 25 percent. However, the success of the FRP can only continue if intense harvest is maintained to prevent the flathead population from rebuilding.
In addition to directed removal via electroshocking, WRD staff have made efforts to examine other control methods, including genetic research that might provide additional long-term assistance in reducing flatheads in the Satilla. Thus far, most genetic research has focused on yielding a triploid (3 chromosome and presumably sterile) flathead catfish that could potentially limit reproduction or reduce the genetic fitness of the population. Researchers with Auburn University have reported progress in successfully producing triploid flatheads in a lab setting. However, many questions remain on the cost, feasibility, safety and effectiveness of this option for use in the wild, and thus additional research is necessary to determine the viability of this potential option before triploid fish are released into the wild.
Flathead Catfish Biology
As one of the largest freshwater catfish found in Georgia, flatheads can reach weights exceeding 120 lb, though most captured are found at smaller sizes (less than 50 pounds).
Often referred to as “mudcats,” “Appaloosa catfish,” or “shovelhead catfish,” they are easily distinguished by their flattened head and free, flap-like adipose fin. The species has yellowish pigmented skin mottled with brown and green; a lower jaw that extends beyond the upper jaw; small eyes; and a non-forked tail. Flatheads may be found throughout various habitats within the river, though they typically prefer deeper waters (e.g. bends in the river) (TPWD 2016).
An apex predator, the diet of flatheads varies and evolves as they mature. Young invertebrates (crayfish, insects, etc.) typically are their primary diet item of flatheads (<300 mm), with fish becoming more prevalent as they grow. Large flatheads (>500 mm) are almost exclusively piscivorous, hence the common use of live bait by fishermen targeting the species. In Georgia, direct predation by larger flatheads has been observed on multiple species of ictalurids (catfish), including various bullhead catfish (Ameirurus spp.), channel catfish (Ictaluris punctatus), white catfish (Ameiurus catus), and even other flatheads (Weller and Robbins 2001). Additionally, they have been noted to prey heavily on several species of centrarchids (panfish), including bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), redar (Lepomis microlophus), spotted sunfish (Lepomis punctatus), and most notably, redbreast. On June 9, 2010, a partially digested (but well intact) juvenile Atlantic sturgeon was recovered from the stomach of a flathead catfish from the Satilla, and while this is the first confirmed field observation of flathead catfish predation on any sturgeon species, it further solidifies the notion that flatheads may consume virtually any available fish prey (Flowers et al. 2011).
The life span of flathead catfish may exceed 30 years, though most do not live that long (Marshall et al. 2009). In Georgia, the spawning season for flatheads occurs from spring through summer. Nesting often takes place in hollow logs, caves, or areas beneath the banks, where the female deposits thousands of eggs and males guard them. Though the number of eggs deposited by a female varies greatly depending on her size, females may lay up to 100,000 eggs at a time (TPWD 2016). After a 4-6 day incubation period, the fry (very young fish) will school together at the nest for several days before eventually seeking independent shelter beneath rocks, roots, and other cover (TPWD 2016). Interestingly, in the Satilla, staff with the Georgia Department of Natural Resources (GA DNR) have noted multiple instances of female catfish responding to high exploitation rates by maturing at smaller sizes and younger ages (Bonvechio et al. 2011). Such a compensatory mechanism has been noted in some marine species, and it’s observance in Satilla flatheads is likely reflective of the population impacts associated with ongoing reduction and removal efforts by GA DNR staff.
Blue Catfish Removal
While the FRP was created with the intended purpose of removing flatheads from the Satilla, a second non-native species has been discovered in the river during removal efforts. In May 2011, GA DNR staff captured a single blue catfish (Ictalurus furcatus) while conducting flathead removals in the Satilla (Bonvechio et al. 2012). Though it is believed that flathead introduction into the Satilla occurred due to illegal stocking by anglers in the mid 1990’s, blue catfish introduction into the river likely occurred when fish migrated to the Satilla River via the intercoastal waterway during high water periods.
A total of seven blue catfish were recovered from the Satilla River in 2011 and two individuals showed up in an access creel survey in 2014. In 2016, a notable spike in blue catfish recruitment was observed with several dozen juvenile individuals being captured, including a gravid adult. Nonetheless, as a large catfish that can exceed 100 lb as an adult, the potential exist for this non-native fish, like the flathead, to have negative implications on native species. As a result, GA DNR staff continue to monitor the blue catfish population in the Satilla while removing all specimens observed during sampling efforts.
Bonvechio, T.F., D. Harrison, and B. Deener. 2009. Populations Changes of Sportfish Following Flathead Catfish Pylodictis olivaris Introduction in the Satilla River, Georgia. Proceedings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies: 63:133-139.
Bonvechio, T.F., M.S. Allen, D. Gwinn and J. S. Mitchell. 2011. Impacts of electrofishing induced exploitation on flathead catfish Pylodictis olivaris population metrics in the Satilla River, Georgia. Pages 395-408 in P. H. Michaletz and V. H. Travnichek, editors. Conservation, ecology, and management of catfish: the second international symposium. American Fisheries Society Symposium 77, Bethesda, Maryland.
Bonvechio, T. F., B. Bowen, J. Mitchell, and J. Bythwood. 2012. Nonindigenous range expansion of the blue catfish Ictalurus furcatus Leseur in the Satilla River, Georgia. Southeastern Naturalist 11/2, 2012.
Flowers, H.J., T. F. Bonvechio and D. Pederson 2011. Observation of an Atlantic Sturgeon Acipenser oxyrinchus eaten by a flathead catfish Pylodictis olivaris. Transactions of the American Fisheries Society 140:250-252.
Jackson, D. C. 1999. Flathead catfish: biology, fisheries, and management. Pages 23-35 in E. R. Irwin, W. A. Hubert, C. F. Rabeini, H. L. Schramm, Jr., and T. Coon, editors. Catfish 2000: proceedings of the international ictalurid symposium. American Fisheries Society, Symposium 24, Bethesda, Maryland.
Marshall, M. D., M. P. Holley, and M. J. Maceina. 2009. Assessment of the flathead catfish population in a lightly exploited fishery in Lake Wilson, Alabama. North American Journal of Fisheries Management 29:869-875.
Texas Parks and Wildlife Department (TPWD). 2016. Flathead Catfish (Pylodictis olivaris). http://tpwd.texas.gov/huntwild/wild/species/catfish.
Weller, R. R., and C. Robbins. 2001. Food habits of flathead catfish in the Altamaha River system, Georgia. Proceedings of the Annual Conferences Southeastern Association of Fish and Wildlife Agencies 53(1999):35-41.
Limited, but aggressive, removals of flathead catfish in the Satilla started in 1996 in an effort to negate the impact on native fish populations.