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Comparison of growth pattern of male Ucides occidentalis (Ortmann, 1897) (Brachyura: Ocypodidae) based on a combination of commercial catches and non-commercial data

Abstract:

Growth estimates of animals are often based on a single data set. The sizes used to determine these estimates can nevertheless be biased by the selectivity of the data source and how well the data represent a population. The average growth of the brachyuran crab Ucides occidentalis (Ortmann, 1897) (Ocypodidae) had been previously estimated utilizing data derived from either commercial catch or scientific field data, consequently generating conflicting results. We determined the average growth of male U. occidentalis by analyzing commercial catch data alone and, subsequently, estimated average growth from a combination of the same commercial data with scientific data collected in situ in mangrove areas (i.e., combined data). Size frequency distributions were constructed using Kernel density estimators, characterizing the modes as Gaussian components. A multi-modal approach was used to select one of five growth models (asymptotic, non-asymptotic, and versatile) that most closely represented the average growth estimated from both cohorts of combined data, which had previously been identified through modal progression, and commercial data. The case 1 of the Schnute model was selected as the best model by Akaike Information and Bayesian Information criteria for both commercial and combined data sets. A convex growth curve was generated for the commercial data (asymptotic growth), whereas an inverted vertical sigmoidal curve was generated for the combined data (non-asymptotic growth). The data sets differed in that commercial data were represented by adult individuals, whereas the combined data included juveniles and adults. This difference significantly affected the average growth estimates calculated for each data set. The growth pattern of male U. occidentalis is best described by a non-asymptotic growth curve, which is consistent with that reported for females of this species.