Length-Weight Relationships and Potential Biases for Alligator Gar (Atractosteus spatula) from Texoma Reservoir, Oklahoma

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Richard A. Snow
Michael J. Porta
Clifton R. Sager


Alligator Gar (Atractosteus spatula) is the largest fish species found in Oklahoma, which makes obtaining field measurements (particularly weight) by fisheries managers or recreational anglers challenging. A method to overcome the logistical hurdles associated with handling and measuring large fish in the field would be beneficial to managers and anglers. Therefore, the objective of this study is to develop length-weight and length-length relationships for Alligator Gar collected from Texoma Reservoir, Oklahoma using total length (TL), standard length (SL), and girth (G) measurements to predict weights and length measurements of Alligator Gar. A total of 339 Alligator Gars averaging 1,666 mm TL (range = 590 to 2,357 mm TL) and weighing 38.2 kg (range = 0.77 to 105.3 kg) were used in this evaluation. No significant differences in weight of Alligator Gar were detected between sex or season (winter-spring and summer-fall), so all fish were pooled for the remaining analyses. All simple linear regression and multiple regression models produced significant relationships (P ≤ 0.05), were highly correlated (r 2 = 0.88 to 0.99), and mean predicted error values were < 13% for all models. However, the simple linear regression model using TL and the multiple regression model using TL and G were the best predictive models to estimate weight in this evaluation. All weight and length estimates predicted with regression analysis were not statistically different than actual Alligator Gar weights and lengths. Visual inspection of weight bias plots suggests little bias between predicted and actual weights for Alligator Gar ≤ 60 kg, but became more variable for fish > 60 kg. However, the simple linear regression model using TL and the multiple regression model using TL and G produced less biased weight estimates for fish up to 80 kg, but appeared to underestimate weights of Alligator Gar ≥ 100 kg. All of the models evaluated in this study provide managers and anglers with a relatively accurate estimate of Alligator Gar weights from Texoma Reservoir and provides fisheries managers with weight-length information to which other Alligator Gar populations can be compared.

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Applied Ecology & Conservation