Abstract

Estimation of the age distribution of fish in different fisheries sectors is a necessary tool for age-based modeling and stock assessment. Two methods of estimating ages from fork lengths of gray triggerfish (Balistes capriscus) sampled from both commercial and recreational sectors in Gulf of Mexico (Gulf) fisheries are compared and described. A multinomial model was used to estimate the probability (± standard error) of a fish of a particular length class (25 mm length categories) occurring in a particular age class. This model was based on age and growth data derived from hard part analyses combined from numerous studies throughout the Gulf. An age frequency distribution was then developed for each fish in the aforementioned fishery dependent data sets, and those frequencies were aggregated for all fish in a particular data set to form an overall age frequency distribution. The more known technique of estimating age from length using an inverted form of the von Bertalanffy growth function was also used. The categorical modeling technique allowed the calculation of standard error for each age class in the overall frequency distributions, which estimation of age using inverted von Bertalanffy functions does not make possible. Finally, mortality estimates of Gulf gray triggerfish are derived using the slope of the descending limbs of the age frequency histograms.

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