Movement and Habitat Use of Alligator Gars in the Escambia River, Florida

Abstract

In Florida, the population status of the Alligator Gar Atractosteus spatula is unknown, and harvest of this species was prohibited in 2006. Although abundance estimates are needed, first information about its habitat use and life history is required. We examined movement, habitat use, and home range of Alligator Gars in the Escambia River, an unregulated coastal river in Florida. Twenty-two fish (TL range = 92–193 cm) were captured by using large-mesh gill nets and were tagged with external transmitters. Detachment of tags resulted in 16 fish being tracked for the study (tag retention time = 2–19 months). Seasonal movements of fish were monitored by active daytime tracking and via fixed-station receivers to determine home and core ranges. Results suggested that Alligator Gar movement was seasonal and related to water temperature. Mean linear home ranges and core ranges were each approximately five times smaller during the cold season (water temperature ≤ 15°C) than during the warm season (>15°C). Diel movement and habitat information was collected (N = 8 Alligator Gars per season) from arrays of fixed-station receivers that recorded data continuously for 24 h during deployment. Individuals moved little and at a lower travel rate during 24-h periods in the cold season, whereas they became highly mobile during the warm season, moving at a higher travel rate. Alligator Gars spent proportionally more time in main-channel habitat (62.5%) during the warm season and in off-channel habitat (84.2%) during the cold season, but no difference in diel use of these habitats was evident between seasons. An understanding of movement patterns and habitat use could lead to increased catch, thereby improving the accuracy of abundance estimates and the reliability of population assessments. Comprehensive knowledge of these behaviors should help to guide conservation and management efforts in regulated and unregulated rivers throughout the Alligator Gar’s range.

Received January 24, 2017; accepted June 9, 2017Published online August 10, 2017

ACKNOWLEDGMENTS

We are grateful to the FWC Blackwater Research and Development Center staff for providing assistance during this research, especially Randy Simmons for his work in recovering lost tags and receivers. We also thank the staff of the USFWS office in Panama City, Florida, for their cooperation during the initial stages of this research and for their continued support throughout the project.