Estimation of the Length‐at‐Age Relationship of Mississippi's Spotted Seatrout

Spotted Seatrout Cynoscion nebulosus are a highly valued recreational inshore species in Mississippi coastal waters. The accurate description of the length‐at‐age relationship is critical for assessment efforts of the stock. Because Spotted Seatrout exhibit small‐scale movements, the stocks in the Gulf of Mexico are managed as state‐specific units. Therefore, local demographic estimates of length at age are needed for assessment. We estimated the length‐at‐age relationship of Spotted Seatrout in Mississippi by using tag recapture records and otolith‐derived age estimates. Three nonlinear length‐at‐age models were fit to sex‐aggregated, tag recapture data and four nonlinear length‐at‐age models were fit to sex‐specific, otolith‐derived age data. For each suite of models, model support was determined using Akaike information criteria. The Francis (1988a) GROTAG method had the greatest support of the three models fit to the tag recapture data, and the resulting parameter estimates from the model were L∞ = 550.8 mm and k = 0.45/year. The three‐parameter logistic model had the greatest support of the four models fit to the otolith‐derived age data for both males and females and the resulting parameter estimates of L∞ were 605.3 mm TL for females and 574.9 mm TL for males. The results of this study indicate that (1) the Francis (1988a) GROTAG model was the best‐supported method for the determination of the von Bertalanffy growth function parameters from tag recapture information, and (2) the von Bertalanffy growth function may not be the best model to describe the length‐at‐age relationship of Mississippi's Spotted Seatrout. This work highlights the utility of using multiple sources of length‐at‐age information and fitting multiple models to enhance both the description of the length‐at‐age relationship and to determine biases that occur in both. Received July 13, 2015; accepted November 3, 2015