Success of Morphometric Gender Identification of Alligator Gar

We attempted to discriminate the gender of 258 Alligator Gar Atractosteus spatula using a non-lethal technique based on morphometric ratios. Fish were collected from seven different populations and ranged in size from 591 – 1,920 mm SL.  Application of a classification method based on two different body measurement ratios exhibited accuracy rates of 98.5% for males and 86.1% for females.  However, this method classified 29% as unknown. A cross-validated discriminant analysis using all fish exhibited accuracy rates of 83.7% for males and 88.8% for females. A logistic regression based on the success of the discriminant analysis suggests fish >1100mm in SL are easier to identify using the morphometric ratios (≥90% accuracy), likely because the changes in body shape are associated with sexual maturity. Current methods involve either the lethal gross examination of gonads or time-consuming assays.  Our easy-to-apply technique provides a non-lethal, cost-effective alternative beneficial to Alligator Gar management and conservation efforts ranging from broodstock collections to studies of life history and population dynamics.