Bits & Pieces: Gator Gar Diets and Florida Bass

Field Research: Gator Gar Diets

The alligator gar was once widely maligned as a nuisance species, resulting in unrestricted har-vest and targeted removal from many native waters. Concurrent with overharvest, habitat loss and degradation also caused populations of alligator gar to suffer, to the point that gar numbers were critically reduced or even extirpated from waters where they were once historically abun-dant. In recent decades, the recognition of alligator gar as an ecologically important species, along with their growing popularity as a sportfish, has led fishery agencies to undertake more research to better understand the biology of this fascinating species.

A recent study by the Oklahoma Department of Wildlife Conservation (ODWC) sought to un-cover seasonal food habits and prey selectivity of alligator gar in Lake Texoma, an 85,000-plus-acre reservoir straddling the Oklahoma/Texas border.* Since the ODWC is planning to reintro-duce alligator gar into their native waters, studying their food habits would offer insights into their potential impacts on populations of other fish species.

Gar were sampled with gill nets and also from angler catches and were pooled into two seasonal groups: winter-spring and summer-fall. Stomachs were analyzed from 138 gar ranging in size from 23 to 91 inches. Most gar (91 percent) in winter-spring had empty stomachs, while 83 per-cent collected in summer-fall had at least one identifiable prey item. Stomachs contained an average of 1.2 prey items, and gar were primarily fish-eaters, with 13 identified fish species consumed.

During winter-spring, only gizzard shad and smallmouth buffalo were found in stomachs. In summer-fall, gizzard shad had the highest percent occurrence in stomachs, followed by com-mon carp, river carpsucker, striped bass, grass carp, and smallmouth buffalo, among other spe-cies with lesser occurrence. Suckers and carps made up more than 60 percent of all diet items and also dominated diets by weight and number. The study demonstrated a significant relation-ship between gar length and prey length, with prey sizes eaten ranging from 8.5 to 42 inches long.

The researchers also studied whether alligator gar selected certain types of prey over other types. This was determined by setting juglines from June through September of two years, with hooks baited with a dead whole fish from a pool of bait species chosen at random: largemouth bass, white crappie, catfish, gizzard shad, buffalo, and river carpsucker. Of the 101 gar caught on juglines, only buffalo and river carpsucker were positively selected by gar. Gar selected neu-trally for gizzard shad, and selected against catfish, largemouth bass, and crappie.

The researchers conclude that while alligator gar consume both non-game and game species in Lake Texoma, they mostly eat non-game species, similar to the findings of other studies. And along with incorporating other fish monitoring data, these results can help ease concerns regarding the effects of alligator gar reintroductions on sportfish species, although effects on non-game species also should be considered.

Dr. Rob Neumann

*Snow, R. A., and M. J. Porta. 2021. Seasonal food habits and prey selectivity of alligator gar from Texoma Reservoir, Oklahoma. J. Southeast. Assn. Fish. Wild. Agencies. 8:15-22.

Genetic Investigations: A New Look at Florida Bass Introductions

For more than 30 years, agencies have introduced Florida bass, a species now known to be separate from largemouth bass, into waters with largemouth bass, intending to increase the size potential of the population, production of trophy-size bass, or catch rates of large fish. Much of the impetus for these introductions comes from angler requests to increase the size of bass in their local waters. As a result, most stockings have been done by state management agencies, though unofficial or illegal introductions have occurred and fish have moved among water bodies.

Geneticists have long noted the tendency of first-generation hybrids of mixed stocks to show heterosis or hybrid vigor, resulting in some of these objectives being achieved in some waters, but not others. Several states outside the natural range of Florida bass have state records that were products of such introductions.

Once Florida bass are stocked, they readily spawn with native fish and their offspring continue to mix, resulting in populations dominated by backcrossed individuals, sometimes called Fx generations, typically dominated by largemouth genetics, with the percent of Florida genetics somewhat dependent on environmental and other factors.

Due to a lack of longer-term evaluations of the effects of stocking, biologists from the Arkansas Game & Fish Commission studied the bass population of Lake Ouachita in Arkansas that’s been stocked with over 800,000 fingerling Florida bass between 2007 and 2015.* They collected 1,000 bass and determined the level of genetic introgression, and evaluated stage of maturity, annual mortality rate, size structure, condition, and growth rate. They also compared tournament catches of large bass prior to stockings and afterward to see whether catches of 5-pound and larger bass increased after Florida bass introductions.

Results showed that the genetically mixed bass didn’t mature earlier, survive longer, show improved body condition, or have greater growth potential compared to native largemouths. As for catchability, there was no difference between time required to catch a 5-pound or larger bass in tournaments before and after introductions. They concluded that a stocking program resulting in a subtle shift toward Florida bass genetics won’t increase the trophy potential of a fishery.

In many of the reservoirs of the south-central U.S. stocked with Florida bass, pure Floridas exist at very low levels, and first-generation hybrids occur with decreasing frequency over time as bass continue to backcross. This study suggests that this practice doesn’t improve population characteristics for recreational fishing. The more adverse the environment for Florida bass (more different from their native habitat), the faster Florida bass genetics dissipate. Regions most likely to see dramatic increases in bass size due to stocking, such as California and Texas, are more similar to native waters. Conversely, this team found no evidence of what’s called “outbreeding depression,” a decline in population viability—reduced survival or reproduction—following introduction of non-native genetics, which some scientists had predicted might occur due to Florida bass introductions. But the high cost of Florida bass production and introduction makes it a questionable strategy.

Steve Quinn

*Lusk, S. C., C. R. Middaugh, and A. A. Asher. 2023. Evaluation of population characteristic differences between the largemouth bass and its backcross following a long-term Florida bass stocking effort. N. Am. J. Fish. Mgmt. 43:603-617.

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