A simple age verification method is presented for centrum edge analysis (CEA) of elasmobranch species. In this method, a binomial model is linked with a von Mises distribution for circular data, taking the characteristics of the CEA data into account. The periodicity of growth band pairs is categorized as no cycle, an annual cycle, or a biannual cycle. Three models are then constructed according to different periodicities. We use the Akaike information criterion (AIC) to determine which model is the best. The models were applied to the shortfin mako shark ( Isurus oxyrinchus ) data collected in the North Pacific to identify the best periodicity model. The AIC best-fitting model was one involving an annual cycle. The general performance of the method was evaluated using simulated data of various sample sizes, formation times, and durations of growth band pairs. The simulation trials showed that the performance of the method was satisfactory with moderate sample sizes. This method should improve the accuracy of age determination and could be applied to all species that have periodic growth band pairs.

We determined the age and growth rates of male and female shortfin makos, (Isurus oxyrinchus), from the western and central North Pacific Ocean. Growth band pairs were counted on half-cut vertebral centra using a shadowing method. In this method, we focused on the ridges on the surface of the centra, consisting of a convex and concave structure. After comparing four enhancing methods, we decided on the use of shadowing method for aging. Vertebrae from 128 males and 147 females were examined. The centrum edge analysis suggested annual band pair formation. Von Bertalanffy growth curves were fitted separately to the length-at-age data for males and females with birth length fixed. Until approximately 7 years of age, both sexes showed similar growth rates; thereafter, males showed a significantly slower growth rate compared to females. It was suggested males and females mature at approximately 6 years and 16 years, respectively. These life-history characteristics suggest relatively low productivity for this species, which agrees with reports on populations in other geographic regions.

Shortfin mako, Isurus oxyrinchus, is a highly migratory shark with a worldwide distribution. Despite recent global concern and intensive ecological studies on this species, little is known about its reproduction, owing to a paucity of information on mature females. We investigated the size-at-maturity and reproductive traits of shortfin mako in the western and central North Pacific. Males attain maturity at a much smaller size (156 cm) than females (256 cm). The positive relationship between maternal size and litter size indicates that fecundity increases as the female grows. The seasonal trends in the gonadosomatic index of mature individuals and the presence of females in early pregnancy confirmed that mating occurs from spring to summer. From monthly changes in embryonic body lengths, averaged per litter, and the seasonal occurrence of neonates, we infer that parturition occurs from winter to spring and the gestation period is 9–13 months. There was a negative correlation between embryonic developmental stages and environmental temperature for females in various stages of pregnancy. The productivity of this species may be higher than previously thought, considering the estimated gestation period and size-related fecundity.