Recently Documented Tilapia Oreochromis spp. Population in Newnan’s Lake
By Jason O’Connor and Chris Anderson
Tilapia Oreochromis spp. are members of the cichlid family that are native to North Africa and the Middle East (Figure 1). At least two species of Tilapia are well-established throughout peninsular Florida. Blue Tilapia Oreochromis aureus were introduced to the state (via research ponds) by FWC’s predecessor the Florida Game and Fresh Water Fish Commission in 1961 to evaluate their utility as food, game, forage and weed control within the state. Some of these fish were distributed to the public and were subsequently released into freshwater ecosystems in south-central Florida. Nile Tilapia Oreochromis niloticus have been collected in Florida since at least 1972, however, details of their introduction and establishment are less well-documented than for the Blue Tilapia. The two species readily hybridize in the wild, and many specimens collected in Florida exhibit hybrid traits. Both species are largely herbivorous, consuming a mix of plant matter, detritus, and occasionally zooplankton, small insects and fish. Tilapia are farmed at aquaculture facilities throughout the state, and established wild populations support commercial fisheries in central and southern portions of the peninsula. Tilapia are not traditionally sought by recreational anglers, but they do support localized bowfishing oriented recreational fisheries, often in springs and spring runs (e.g., Silver Glen Springs).
Although initially introduced in south-central parts of the state, Tilapia have spread throughout much of peninsular Florida, and now occur in most major drainages east and south of the Suwannee River, with a few isolated records from other states surrounding the panhandle (Figure 2). The Orange Creek Basin, a sub-drainage of the St. John’s River in north-central Florida, is one of the northern-most occupied watersheds in the state (Figure 3). Major lakes in the Orange Creek Basin include Orange, Lochloosa and Newnans. The fish communities in these lakes have been intensively sampled for decades, and although Tilapia have been regularly documented in Orange and Lochloosa lakes for over 15 years, they are rarely encountered on Newnans Lake. Prior to 2021, there had only been 2 documented records of Tilapia in Newnans (both in April 1999), despite annual fish surveys using a variety of sampling methods since 1989. However, we observed a single Tilapia in March 2021 while electrofishing in Prairie Creek, the primary outflow of Newnans Lake. Then in November 2021, we collected two individuals in the northern end of the lake while surveying for Black Crappie Pomoxis nigromaculatus. The following spring (February-March 2022), we observed numerous Tilapia in throughout the lake while surveying for Largemouth Bass. The majority of the individuals collected have been around the same size (35-43 cm), which suggests that much of the population may be from a single annual cohort.
Unfortunately, we don’t have enough information to determine whether the current population expansion of Tilapia in Newnans represents a novel invasion or population growth of an existing low-density population. If this represents a novel invasion, it may have been caused by human-mediated translocation or via natural immigration from established populations within the Orange Creek Basin. There are numerous anecdotal reports of people moving non-native fish among waterbodies in Florida, particularly for species of recreational or commercial importance. It is also possible that the frequency of historically high water levels throughout the Orange Creek Basin since 2017 has facilitated movement of individuals from established populations to Newnans via a series of creeks and canals. Alternatively, it is conceivable that an established population has existed in Newnans since at least 1999 but has occurred at densities below the detection limits of our sampling gears. If this is the case, then the recent population expansion may have been a result of increased access to quality spawning habitat due to sustained high water levels, which increased recruitment in recent years.
Regardless of whether we are witnessing a new invasion of Tilapia or simply a population boom of a historically low-density population, this population expansion has resulted in the greatest frequency of Tilapia observations/collections by FWC in Newnans in the last two decades. Although research on the impacts of Tilapia in large, natural ecosystems is lacking, pond/mesocosm studies on the impacts of high-density Tilapia populations have documented substantial reductions of age-0 production, recruitment, and growth of Largemouth Bass Micropterus salmoides, the most popular freshwater sportfish in Florida. The existence of the long-term fish community dataset provides a unique opportunity to evaluate potential effects that Tilapia establishment/population expansions have on fish populations/communities in a large, natural ecosystem. This highlights the importance of long-term sampling programs (e.g., Freshwater Fisheries Long-term Monitoring Project) for tracking the spread, and abundance of non-native fishes so that their potential impacts on native fish populations and communities can be assessed. Additionally, the Newnans population is currently one of the northernmost established Tilapia populations in Florida. Since climate change will likely facilitate expansion of their established range into the Florida panhandle, information on the effect of Tilapia invasion/expansion on native fish communities in Newnans Lake would inform fisheries managers about potential undesirable impacts if/when new invasions/expansions occur.