Comparison of techniques of back-calculation of growth and settlement marks from the otoliths of three species of Diplodus from the Mediterranean Sea

We developed a model of back-calculation of fish size from otoliths that co uld accommodate both changes in the relationship between otolith and somati c growth that occur through time and variation in growth rates among indivi duals. We used this model to back-calculate estimates of size and growth fr om otoliths of three species of Diplodus from the Mediterranean Sea. The ou tcomes of our model were compared with those of three other models and with growth curves estimated directly from populations of fish in the field. We found that our new model produced estimates of size-at-age that were close r to those observed in the field than the biological intercept, time-varyin g growth, and body proportional models. Comparison of profiles of increment width from otoliths of newly settled and juvenile Diplodus puntazzo and Di plodus vulgaris showed that these species formed a settlement mark, where i ncrement width declined at settlement. In contrast, a settlement mark was n ot evident in the otoliths of Diplodus sargus. However, settlement of all s pecies coincided with a sharp decline in somatic growth rate. Thus, growth rate may provide a means of estimating the timing of settlement in species that do not display a marked change in increment width.