REPRODUCTIVE-BIOLOGY OF FEMALE STRIPED DOLPHIN (STENELLA-COERULEOALBA) FROM THE WESTERN MEDITERRANEAN

Data on age and length at sexual maturity, calving interval, lactation period, and ovulation and pregnancy rates were analysed from 54 femal e striped dolphin collected during the Mediterranean morbillivirus epi zootic. Age was determined by counting growth layer groups in tooth de ntine, and reproductive status was determined by the macroscopic exami nation of the ovaries and the uterus. Age at sexual maturity (ASM) was estimated using two different methods; giving average estimates of 12 and 12.3 years. The average length at sexual maturity was 187 cm and the calving interval was four years. The annual pregnancy rate (APR) w as calculated using two different criteria. In the first, only females that were pregnant at the time of death, as evidenced by the presence of a foetus, were incorporated in the calculations. This method gave ail estimate of 8.9% as the apparent pregnancy rate of the dolphins ki lled by the epizootic. The second method incorporated in the calculati ons females that were pregnant at the time of death and females that h ad young corpus albicans in the ovaries and a distended uterus. This m ethod is considered to reflect the true pregnancy rate of the populati on and gave an estimate of 25%. Estimates of ovulation rate (0.401) an d lactation period (16 months) were considered to be potentially affec ted by the disease and, therefore, biased. These estimates reflect a p eculiar situation of the diseased dolphins but are useful for Comparat ive purposes. Estimates of ASM and APR, parameters which are not likel y to be affected by the disease, differed markedly from those of other Stenella populations and could indicate a density-dependent response. possibly reflecting food limitations.