Validating morphometrics as a non‐lethal tool to determine Arctic Grayling sex.

Abstract Objective Some Graylings ( Thymallus spp.) possess an elongated dorsal fin and other morphological traits that can be sexually dimorphic as demonstrated in European Grayling T. thymallu s. North American Arctic Grayling T. arcticus are assumed to follow these trends, but decisive evidence is lacking. This study aimed to determine whether sexually dimorphic characteristics, including posterior dorsal height, of Arctic Grayling in Interior Alaska can be used to accurately predict fish sex. Methods We used computer imaging software to measure 22 morphometrics on 97 Arctic Grayling of known sex from streams in Interior Alaska and developed a set of binomial models to evaluate the validity of morphometrics as predictors of Arctic Grayling sex. Result Posterior dorsal height was a reasonably accurate predictor of sex (~90% accurate at fork lengths ≥ 300 mm), although models containing additional morphometrics were more accurate (100% accuracy at fork lengths ≥ 250 mm). Conclusion This study presents an affordable, non‐invasive, and replicable method for non‐lethal determination of Arctic Grayling sex using digital images from the field, with potential application to other salmonids.