Satilla River Flathead Catfish Project
The Satilla River historically has been one of the premier sunfish angling destinations in Georgia, with redbreast sunfish being one of the most sought after species. Monitoring efforts, such as tagging and sampling, are critical to the proper management of the flathead population and the recovery of the redbreast sunfish.
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. The current removal method is electro-fishing equipment. This equipment generates a low frequency electrical current in the water, stunning the fish which float to the surface.
Tagging and Removal
From March through April of 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 2008, and between March and May, 96 flatheads were caught and tagged.
These tagging studies were used to obtain baseline information (such as movement, population size, total mortality and fishing mortality) on the Satilla River flathead catfish population. Gathering data on the effect of catfish removal and fishing mortality on the population each year will help biologists gain a better understanding for the amount of effort required to suppress the flathead population while biological and/or genetic controls are developed.
Anglers are still asked to report any fish caught with a tag by any of the following methods: mailing or hand-delivering the tag to the Wildlife Resources Division Fisheries Management office located in Waycross (P.O. Box 2089/108 Darling Avenue, Waycross, GA 31502). Anglers should include their name, address, phone number(s), date of catch, catch location (GPS coordinates if possible or local landmarks, etc.), fish length, fish weight and whether the fish was harvested or released (preferably harvested).
In 2007, a total of 4.399 flathead catfish (25,357 pounds) were removed from the Satilla River. Fifty-three percent of previously tagged fish were recaptured and removed from the 2007 tagging study. Results from the 2007 tagging study indicated an exploitation estimate (fishing mortality) of .526 or 53 percent, a total annual mortality of 37 percent calculated from the otoliths of 484 catfish, and a 40-52 percent reduction in the flathead population as indicated by depletion models. Biologists conclude that the range of different mortality estimates calculated for the 2007 removal ranged from 37-53 percent.
In 2008, a total of 3,285 flatheads (9,398 pounds) were removed from the Satilla River. Similarly to 2007, 50 percent of the previously tagged fish were recaptured and removed from the river in 2008. Results from the 2008 tagging study indicated an exploitation estimate (fishing mortality) of .5 or 50 percent.
Consecutive years of tagging (2007 and 2008) has revealed estimated fishing mortality rates of more than 50 percent each year. Biologists find this rate encouraging considering that past modeling estimates indicate significant declines in the size and numbers of Satilla River flathead catfish when fishing mortality rates are higher than 25 percent.
Because similar successful results were obtained for tagging in 2007 and 2008, tagging will not be conducted in the future and instead sampling efforts will focus solely on the removal aspect of the project. In 2009, a total of 5,788 flatheads (7,815 lb) were removed and in 2010, a total of 6,289 flatheads (11,101 lb) were removed from the Satilla River.
Since the implementation of the full-time flathead management program in April 2007, more than 53,671 pounds of flathead catfish (19,761 fish) have been removed from the river. The size structure of the flathead population has been affected with the average size fish removed dropping from 5.8 lb in 2007, to 2.9 lb in 2008, to 1.4 lb in 2009, but slightly increased to 1.8 lb in 2010. Biomass per effort show a similar trend and had also declined from 57.1 kg/hr in 2007, to 23.6 kg/hr in 2008, to 23.6 kg/hr in 2008 to 19.9 kg/hr in 2009, but increased to 31.1 kg/hr in 2010.
Maintenance control of flathead catfish in the Satilla River appears possible given our reported changes in the size structure and biomass of the population, but intense harvest needs to be maintained to prevent the flathead population from rebuilding, especially during high water years, where strong recruitment has been demonstrated by the introduced flathead population.
The project’s lead biologist has made efforts to look at other control methods, including genetic research that might yield a triploid (3 chromosome) flathead catfish. Introduction of this fish could potentially limit reproduction or reduce the genetic fitness of the population. However, additional research is necessary to determine the safety and effectiveness of this option.
Researchers with Auburn University have recently reported tremendous strides in artificially spawning triploid flatheads. Analysis revealed a 100 percent triploid induction rate. This research indicates that triploid flathead catfish can reliably be produced in a lab setting.
In the future, Division biologists are planning additional research, including possible future collaboration with Auburn University on the sexual reproduction of triploid flathead catfish.
Monitoring efforts of the flathead catfish population and redbreast sunfish population will provide the best guideline. It is unknown how removal efforts will affect these fish populations over time. Therefore, the length of the project is undetermined at this time.
The Satilla River is a typical floodplain driven ecosystem. Large amounts of beneficial nutrients enter the system during high water periods.
Ancedotal fishing reports suggest that the redbreast sunfish has begun to make their comeback in the Satilla, but there simply has not been enough time for this population to recover. During the spring and summer of 2010, favorable water conditions (high water) for redbreast sunfish production have persisted on the Satilla. Such conditions combined with continued efforts to reduce the flathead catfish population will hopefully result in the redbreast sunfish population rebounding to historical levels throughout the entire river.
Spring standardized electro-fishing efforts in 2010 did reveal a large increase in the catch per effort of redbreast sunfish (88 fish per hour in 2009 compared to 208 fish per hour in 2010). Biologists caution that the majority of these fish were less than four inches in length and it is currently inconclusive as to whether or not these fish will survive to the desired harvestable size of 7-8 inches. This increase also may be due to flathead reduction, but other factors, such as water level and fishing effort may also have been an important influence on the increase of redbreast sunfish abundance.
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