Comparison of Female Reproductive Patterns of Two Populations of Alligator Gar in Coastal Louisiana

Alligator gar populations have declined in much of the species’ native range but are considered secure in south Louisiana. The objective of this study was to quantify and compare female reproductive patterns of alligator gar collected from Terrebonne Estuary (N=50) and Rockefeller Wildlife Refuge (N=75).  Fish were collected from September 2011 to August 2012 using gillnets, juglines, and bowfishing. To assess female reproductive patterns, plasma estradiol concentrations were quantified using ELISA, reproductive phase was classified (immature, developing, spawning capable, regressing, regenerating) using gonad histology. Terrebonne estradiol concentrations peaked in April (0.623 ng/ml) followed by declines in May (0.255 ng/ml) and June (0.14 ng/ml). Rockefeller estradiol concentrations peaked in March (2.34 ng/ml) followed by declines in April (1.09 ng/ml), May (0.162 ng/ml), and June (0.099 ng/ml).  Regressing females (post-spawn) were most prevalent in Terrebonne during July (30%) and in Rockefeller during June (40%).  The majority of fish spawned during May and June in Terrebonne and April and May in Rockefeller.  Previous studies have examined gonad histology in alligator gar and other gar species in south Louisiana, but this is the first study to couple examination of gonad histology and reproductive steroid levels to more accurately define reproductive patterns.