Body growth and reproduction of individuals of the sciaenid fish Stellifer rastrifer in a shallow tropical bight: A cautionary tale for assumptions regarding population parameters

Knowledge of population parameters and the ability to predict their responses to environmental changes are useful tools to aid in the appropriate management and conservation of natural resources. Samples of the sciaenid fish Stellifer rastrifer were taken from August 2003 through October 2004 in shallow areas of Caraguatatuba Bight, southeastern Brazil. The results showed a consistent presence of length-frequency classes throughout the year and low values of the gonadosomatic index of this species, indicating that the area is not used for spawning or residence of adults, but rather shelters individuals in late stages of development. The results may serve as a caveat for assessments of transitional areas such as the present one, the nursery function of which is neglected compared to estuaries and mangroves. The danger of mismanaging these areas by not considering their peculiarities is emphasized by using these data as a study case for the development of some broadly used population-parameter analyses. The individualsʹ body growth parameters from the von Bertalanffy model were estimated based on the most common approaches, and the best values obtained from traditional quantification methods of selection were very prone to bias. The low gonadosomatic index (GSI) estimated during the period was an important factor in stimulating us to select more reliable parameters of body growth (L∞ = 20.9, K = 0.37 and Z = 2.81), which were estimated based on assuming the existence of spatial segregation by size. The data obtained suggest that the estimated mortality rate included a high rate of migration of older individuals to deeper areas, where we assume that they completed their development.