Spatiotemporal Patterns of Gars in Two Subtropical Estuaries

Abstract Characterizing drivers of estuarine fish assemblages provides valuable insights into estuarine ecology and how each species may react to stressors such as climate change and anthropogenic disturbances. Although they are known to inhabit estuaries, gars are managed as freshwater species and little is known about their movements, reproduction, or other ecological requirements. This study quantitatively describes and compares spatiotemporal dynamics of Alligator Gar ( Atractosteus spatula ), Spotted Gar ( Lepisosteus oculatus ), and Longnose Gar ( Lepisosteus osseus ) in two subtropical estuaries in the northwestern Gulf of Mexico. Thirty-three years of data from a long-term monitoring program were used in hurdle models to identify abiotic factors that impacted gar presence and abundance and to map spatial hot spots to find spatiotemporal patterns within the species assemblage. Within both Galveston Bay and Sabine Lake, season and salinity were the primary drivers of gar presence and abundance for all three species. Alligator Gar were more abundant in higher salinity areas than Spotted Gar and Longnose Gar. Longnose Gar were most abundant in areas with the lowest salinity. All species were most abundant in the spring on the eastern side of both estuaries, correlating strongly with the spring spawning season and marshes and tidal creeks that are less anthropogenically disturbed and frequently flooded. The results of this study suggest potential niche partitioning through species-specific salinity thresholds and the importance of undisturbed marsh habitat and tidal creeks.