Georgia Wildlife Resources Division
2067 U.S. Hwy. 278, SE, Social Circle, GA 30025
In an effort to negate the impacts of flathead catfish on native fish populations, Wildlife Resources Division 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, GA DNR 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.