Reproductive Ecology of Alligator Gar: Identification of Environmental Drivers of Recruitment Success

Alligator gar (Atractosteus spatula) exhibit many characteristics of a periodic life-history strategy, including extended longevity, late maturity, high fecundity, and variable recruitment success. Observations of alligator gar spawning events indicate that recruitment in inland waters may be linked to spring and summer flood pulses and the availability of floodplain spawning habitats. However, because data have mostly come from observation and not formal experimentation, it is unknown whether these data represent true requirements or if they simply reflect conditions that were easily observed. Therefore, we reviewed existing data regarding alligator gar spawning and early development to draft habitat suitability criteria related to recruitment success and then tested these criteria against historic annual recruitment variability (i.e., year-class strength) in the Trinity River and Choke Canyon Reservoir, Texas. Habitat suitability criteria were proposed for water temperature (20 to 30 °C, coinciding with spring and summer), hydrology (inundation of floodplain habitats to a depth of at least 1 m for a minimum of 5 days), and spawning habitat characteristics (open canopy with herbaceous or small woody vegetation within 0.5 m of the water surface where there is little or no flow). In both the Trinity River and Choke Canyon Reservoir, we found that historic annual recruitment of alligator gar generally corresponded closely with the availability of suitable hydrologic conditions during spring and summer. Alligator gar recruitment was highly variable in both systems with above expected recruitment only occurring in about 30% of the years. The strongest two year classes comprised about half of the population in each system and were produced in years with large, long duration flood pulses during June and July. While additional research is needed to refine the proposed habitat suitability criteria, our study verifies a link between alligator gar recruitment success and the availability of floodplain spawning habitats during the spring and summer in inland waters.

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