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Individual growth estimation of Ucides occidentalis (Brachyura, Ocypodidae) in the Gulf of Guayaquil, Ecuador by indirect methods and multi-model selection

Abstract:

Ucides occidentalis (Ortmann, 1897) is a commercial crab in the Ecuadorian continental coast, however, little knowledge is available about its biology. A very important aspect for stock assessment and fisheries management is the species' individual growth. In this paper U. occidentalis growth in males and females was determined by indirect methods and the multi-model approach. By Kernel density estimators size frequency distributions were built, separating their Gaussian components by the Bhattacharya's method. Using modal progression, the cohorts were identified, and one was selected to apply asymptotic, non-asymptotic, and Schnute's versatile growth models. The best fit model was selected using the Akaike and Bayesian weights. Case 1 of Schnute was the winner model in both sexes, asymptotic in males with L∞ = 93.62 mm cephalothorax width (CW), k = 0.57 year-1 and t0 =-0.02 year-1, but it was non-asymptotic for females with an inflexion point in 2.49 years that corresponded to 73.72 mm CW. The type of individual growth of this species varies between sexes, which may be linked to reproductive issues; however, we should consider the data source and their impact on the interpretations that we can draw about individual growth. Therefore, for future studies, using other sources of information such as commercial catches or capture-recapture to validate the results presented, is recommended.Ucides occidentalis (Ortmann, 1897) is a commercial crab in the Ecuadorian continental coast, however, little knowledge is available about its biology. A very important aspect for stock assessment and fisheries management is the species' individual growth. In this paper U. occidentalis growth in males and females was determined by indirect methods and the multi-model approach. By Kernel density estimators size frequency distributions were built, separating their Gaussian components by the Bhattacharya's method. Using modal progression, the cohorts were identified, and one was selected to apply asymptotic, non-asymptotic, and Schnute's versatile growth models. The best fit model was selected using the Akaike and Bayesian weights. Case 1 of Schnute was the winner model in both sexes, asymptotic in males with L∞ = 93.62 mm cephalothorax width (CW), k = 0.57 year-1 and t0 = -0.02 year-1, but it was non-asymptotic for females with an inflexion point in 2.49 years that corresponded to 73.72 mm CW. The type of individual growth of this species varies between sexes, which may be linked to reproductive issues; however, we should consider the data source and their impact on the interpretations that we can draw about individual growth. Therefore, for future studies, using other sources of information such as commercial catches or capture-recapture to validate the results presented, is recommended.