Feeding Ecology of Age‐0 Gar at Texoma Reservoir Inferred from Analysis of Stable Isotopes

Abstract

Conservation and restoration of gar (Lepisosteidae) populations in North America are increasingly of interest to fisheries managers. Alligator Gar Atractosteus spatula are being stocked as age‐0 fish in efforts to re‐establish extirpated populations. However, gars are known to be highly cannibalistic in hatcheries, suggesting that age‐0 Alligator Gar introduced into natural habitats may face predation pressures from other gar species, limiting the likelihood of released fish recruiting to the population. Furthermore, introduced age‐0 gar may not have the proper prey resources for rapid growth that would facilitate recruitment to adulthood. Texoma Reservoir, located on the Oklahoma–Texas border, hosts four native gar species, including the Alligator Gar, whose population is supported by supplemental stocking of age‐0 fingerlings. We investigated feeding by age‐0 gar to obtain a baseline level of trophic ecology for this group of fishes, including the potential for poststocking cannibalism. Food webs were reconstructed via analysis of carbon (δ13C) and nitrogen (δ15N) isotopes using Bayesian mixing model approaches. Isotopic values for age‐0 fish of all four gar species were similar. Invertebrates represented a large fraction of the diet for all gars, followed by Common Carp Cyprinus carpio and Grass Carp Ctenopharyngodon idella. Competitive interactions among Bluegill Lepomis macrochirus, White Bass Morone chrysops, White Crappie Pomoxis annularis, and young gar may occur for invertebrates, shads Dorosoma spp., and Western Mosquitofish Gambusia affinis but are likely short‐lived due to the rapid growth of age‐0 gar after their transition to piscivory. Trophic position of age‐0 Alligator Gar, Longnose Gar Lepisosteus osseus, and Spotted Gar Lepisosteus oculatus was positively related to TL, but this relationship was not observed for Shortnose Gar Lepisosteus platostomus. In Texoma Reservoir, the four native gar species, including stocked Alligator Gar, appear to have adequate food resources for recruitment, with little indication of within‐family or interspecific predation. This suggests that stocked Alligator Gar quickly acclimated to their new environment.

A Review of Grass Carp and Related Species Literature on Diet, Behavior, Toxicology, and Physiology Focused on Informing Development of Controls for Invasive Grass Carp Populations in North America

“…[842] found that stocked grass carp had to be greater than 450 mm in size to ensure they were not eliminated via largemouth bass predation. In Texoma Reservoir (Oklahoma and Texas, USA), grass carp occurred in 33.3% to 38.7% of the stomach content samples of juveniles of four gar species: alligator gar (Atractosteus spatula), longnose gar (Lepisosteus osseus), shortnose gar (Lepisosteus platostomus), and spotted gar (Lepisosteus oculatus) [843]. The size of the grass carp consumed by gar in this study are not directly reported, but the grass carp sampled from the Texoma Reservoir for additional gar diet analyses had 42 to 98 mm total length, whereas the mean lengths of the gar species sampled ranged from 135 mm (shortnose gar) to 194 mm (longnose gar) total length, suggesting that only small juvenile grass carp are susceptible to predation by juvenile gar.…”