Alligator Gar Movement and Macrohabitat Use in the Lower Trinity River, Texas

Abstract

Using acoustic telemetry, we characterized movements and macrohabitat use of 46 Alligator Gars Atractosteus spatula in the lower 180 km of the Trinity River, Texas. Although several Alligator Gars used over 100 km of the river, 83% of the tagged fish had linear home ranges less than 60 km during the 22 months of study. As a result, home ranges of fish that were tagged in different parts of the study area rarely overlapped. Home range size varied by season, with the smallest home ranges occurring in winter. Greatest movements occurred during the spawn (May–June) and postspawn (July–October) seasons, and movements were correlated with increasing water temperatures based on detections of tagged fish at fixed receiver stations. Tagged Alligator Gars were most often associated with main-channel habitats when river stage was at base level and during small flood pulses (<3-m rise). When in the main channel, tagged Alligator Gars selected water that was deeper than the average within their home ranges. In contrast, during large flood pulses (≥3-m rise), tagged fish were found in tributaries and inundated floodplains, regardless of season. Use of tailwater and estuarine macrohabitats was seasonal and limited to fish that had been tagged near those areas. Limited home ranges and observed spatial segregation of fish tagged near the upper and lower boundaries of the 180-km study area suggest that the fish have access to critical habitats needed for reproduction, feeding, and migration within relatively small spatial scales. As such, Alligator Gars in the lower Trinity River do not appear to represent a single panmictic population, indicating that localized rather than regional management efforts would be appropriate.

Received May 18, 2012; accepted April 15, 2013

ACKNOWLEDGMENTS

We thank the staffs of the TPWD Heart of the Hills Fisheries Science Center and River Studies programs for providing field assistance and equipment. Editorial comments by A. Barkoh, R. Betsill, W. Karel, and C. Robertson improved this manuscript. Funding was provided in part by the U.S. Fish and Wildlife Service through the State Wildlife Grants Program Grant T-53-1 to the TPWD Inland Fisheries Division.