Proposed standard weight (Ws) equation and length categories for Utah Chub

Condition indices, such as relative weight (W_r), provide a simple method for comparing length–weight relationships among populations. However, no standard weight (W_s) equation has been developed for Utah Chub Gila atraria, a species of important management focus in the Intermountain West. We obtained length–weight data for 30,541 Utah Chub from 24 populations in Idaho, Montana, Utah, and Wyoming. We used the regression line percentile (RLP), linear empirical percentile (EmP), and quadratic EmP methods to develop average (50th percentile) and above average (75th percentile) W_s equations. Additionally, Froese’s method was used to develop another W_s equation for Utah Chub. Length-related biases were detected in W_s equations developed using the RLP, 50th percentile quadratic EmP, and Froese methods. The linear EmP W_s equations did not exhibit length-related biases for the 50th and 75th percentiles. We propose using the 75th percentile linear EmP W_s equation for Utah Chub between 90 and 410 mm TL. The EmP 75th percentile equation was log₁₀(W_s) = −4.938 + 3.031·log₁₀(TL), where W_s is weight in grams and TL is in millimeters. The English equivalent of this equation is log₁₀(W_s) = −3.335 + 3.031·log₁₀(TL), where W_s is weight in pounds and TL is in inches for 4–16-in Utah Chub. Additionally, we propose that minimum TLs of 100 mm (4 in; stock), 200 mm (8 in; quality), 250 mm (10 in; preferred), 300 mm (12 in; memorable), and 380 mm (15 in; trophy) be used to calculate proportional size distribution (PSD) indices. Better understanding Utah Chub populations using W_r and PSDs will aid managers in assessing management strategies (e.g., biological controls) focused on Utah Chub.