From the river to the estuary: Movements and habitat use of Alligator Gar in Cedar Lakes, Texas

Abstract Objective Although Alligator Gar Atractosteus spatula are known to inhabit river mouths and brackish areas at various life stages, little is known about the residency patterns of Alligator Gar in estuaries. We examined coastal habitat use and movement of Alligator Gar in Texas and analyzed potential environmental drivers of seasonal movement. Methods Alligator Gar were tracked with acoustic tags in the Cedar Lakes region of the Texas Gulf coast, which includes two substantial river mouths and the Intracoastal Waterway. Generalized additive mixed models were utilized to analyze the impacts of water temperature, river discharge, salinity, dissolved oxygen, turbidity, and individual size on movement. Results Individuals utilized both estuarine marsh habitat and riverine habitat seasonally throughout the study, with estuarine detections occurring more frequently in spring–summer (94.0% of detections) and riverine detections occurring more frequently in fall–winter (64.0% of detections). Alligator Gar were mostly absent from the estuary during the coldest months of the year, which was consistent with fishery catch data suggesting their relative absence from estuaries in winter. Fish frequently used the Intracoastal Waterway to travel between habitats (18.8% of detections). Relatively cool water temperatures were predictive of higher rates of movement, and temperature may be a cue for upriver migration in the fall and winter. Conclusions Coastal Alligator Gar overall showed a seasonal preference for productive, shallow estuarine habitat in spring and summer; however, in fall and winter, individuals generally made directed movements into riverine habitat. Our findings indicate that coastal Alligator Gar are highly mobile between estuarine and freshwater habitats and respond to environmental cues to transition between these habitats. Understanding the behaviors and habitat use of Alligator Gar in estuaries will inform future management of the species at the coastal edge of its range.