Otolith microstructure, age, and growth patterns of dolphin, Coryphaena hippurus, in the western Mediterranean

The age and growth of dolphin, Coryphaena hippurus, has been determined in wild specimens between 14.4 and 124 cm fork length (FL) caught off Majorca (Balearic Islands, western Mediterranean). Also, several methods have been applied to validate the results obtained and to assess the aging techniques presently used. In accordance with the sexual dimorphism of this species, the length-weight relationship showed negative allometry in females and iso metry in males. The high correlation between increment counts and known age in 75 reared larvae from 0 to 38 days old (number of increments = 0.3894+0 .9846.days of age; r=0.98) indicated that the daily deposition of growth in crements in sagittal otoliths and regular incremental formation begins on d ay one. This correlation validated the use of otoliths in the aging of 176 juvenile specimens between 16.5 and 58.5 cm FL, in which the minimum and ma ximum ages observed were 47 and 176 days, respectively. Nevertheless, the p rogressive increase in complexity with the ontogenic development of these s tructures suggests that this method may underestimate age in adult fish, pr obably owing to the loss of marginal zones of the otolith during the polish ing process. Thus, from 150 specimens between 65 and 124 cm FL, the interpr etation of annuli from scales gave ages up to 3 years old, whereas readings of otoliths in 36 specimens of the same size interval gave ages between 0 and I year old. Growth parameters were calculated from the age-length relat ionships of otolith and scale readings in juvenile and adult fish, respecti vely, and from the analysis of monthly length-frequency distributions, obta ined in 1990 and 1991 during the exploitation of juveniles from 18 to 70 cm FL (n=4084). The values obtained for L-infinity ranged from 72.4 cm FL in unsexed juveniles and 110.0 cm FL in females both juvenile and adult, where as k ranged from 1.6/year in juvenile and adult females and 2.5/year in uns exed juveniles. Although the results obtained were quite different owing to the different length and age range considered, similar results were obtain ed by comparing the growth performance index (F), and showed the rapid grow th of the species.