Modelling the growth of a protogynous sparid species, Spondyliosoma cantharus (Teleostei: Sparidae)

Abstract

Age determination of fish species is a key process for fisheries management and the accuracy of assessments is highly dependent on age estimates. To model complex life histories such as protogynous hermaphroditism, the growth curve to fit the age-length data should be carefully chosen. For the first time, the first annual growth increment of Spondyliosoma cantharus was validated and several growth functions were applied, in order to find the best growth model. S. cantharus specimens ranged from 2.1 to 38 cm total length and were aged from 0 to 17 years. For the growth functions applied, the hyperbolic modifications of von Bertalanffy curve showed the best fit to the data. Under this model, a change in growth occurs at 8 years, which corresponds to the average age for sex reversal in the species. Estimated total mortality was similar for the two years studied, varying between 0.65 and 0.69 year−1. Natural mortality was estimated by the updated Hoenignls t max-based estimator and the Paulynls-T estimator, ranged between 0.26 and 0.37 year−1. Fishing mortality (0.28–0.43 year−1) and exploitation rate (0.43–0.62) were relatively high, indicating that although the species is not a main target its management needs careful attention.