Life history characteristics of alligator gar, Atractosteus spatual, in the Bayou DuLarge area of southcentral Louisiana

Abstract

The alligator gar Atractosteus spatula is a large, long-lived, physostomous fish that inhabits aquatic habitats throughout the central U.S., ranging from Oklahoma southward to the Gulf of Mexico. Unfortunately, the alligator gar has declined significantly in abundance throughout much of its historic range and is now considered vulnerable to localized extirpation. The goal of this study was to provide basic data on the ecology and life history of a commercially-exploited alligator gar population in south Louisiana. This study also focused on age determination and alternate aging techniques such as sectioned otoliths and sectioned scales. From 10 April 2007 through 21 May 2008, alligator gar were collected with jug lines from Bayou DuLarge and surrounding areas with the aid of a local commercial fisher. A total of 203 male, 125 female and 1 unsexed alligator gar were collected. Sex ratio was approximately 1:1 for catch by month. Overall, female alligator gar were longer, heavier, and had larger girths than males. Alligator gar predominately fed on fishes (34%), although crustaceans (4%) and non-food items (5%) were also found. Based on gonadosomatic index values, spawning occurred from March through May. Gar ages ranged from 1 to 26 years with a mean age of 5 years for males based on sectioned otoliths (N = 194) and sectioned scales (N = 144). Mean age for females based on sectioned otoliths (N = 122) was 5.5 years, and 5.8 years based on sectioned scales (N = 71). In my sample, it appeared male and female alligator gar matured by age 5. The growth rate (k value from von Bertalanffy growth equation) was 0.323 ± 0.017, and annual survival from a catch curve was estimated to be 79.9% (Z = 0.225). Sectioned otoliths yielded the highest precision between readers (0.46, Average Percent Error) and presented fewer complications during age determination as compared to sectioned scales. Life history and age information from this study will aid with understanding the complex and variable nature of the Bayou DuLarge alligator gar population and will be useful to agencies in the development of future management programs for this unique species.