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

Abstract

We developed a model of back-calculation of fish size from otoliths that could accommodate both changes in the relationship between otolith and somatic growth that occur through time and variation in growth rates among individuals. We used this model to back-calculate estimates of size and growth from otoliths of three species of Diplodus from the Mediterranean Sea. The outcomes 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 closer to those observed in the field than the biological intercept, time-varying growth, and body proportional models. Comparison of profiles of increment width from otoliths of newly settled and juvenile Diplodus puntazzo and Diplodus vulgaris showed that these species formed a settlement mark, where increment width declined at settlement. In contrast, a settlement mark was not evident in the otoliths of Diplodus sargus. However, settlement of all species 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.