Stock identification study on elasmobranchs

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Stock identification studies on elasmobranchs, particularly three species of sharks, were conducted using morphological, ecological, and genetic characters. Regarding starspotted dogfish Mustelus manazo, extensive study on stock identification was carried out based upon 1,514 specimens collected from seven localities. Morphological differences between localities were detected by canonical correlation analysis. There were also observed geographical differences in age and growth, showing trend of increase of growth and longevity toward the northern locality. The similar trend was also observed in lenngth at birth. Length and age at maturity showed a tendency of increase with latitude. Litter size showed an increase with parent length and the smallest number in Tokyo Bay at the same length whereas largest in Taiwan. However, the reproductive cycle in Aomori seemed to be quite different from other localities. Food habits also revealed geographical variations, demonstrating an increase in the ratio of stomach content weight to total weight toward south. As a result, it is suggested that there are at least five stocks of the starspotted dogfish around Japan. Regarding shornose spurdog Squalus megalops, paopulation studies were conducted using morphological and gentic characters based upon 133 specimens collected from seven localities in the world. Significant differences were observed in shape of dermal denticles and pectoral and caudal fins between localities, resulting in the separation of three groups, the Mediterranean, South Africa, and Japan and Australia. Genetically, three groups, Japan, Australia and South Africa were distinguished. For these reasons, the species complex was divided into four groups, Japan, Australia, the Mediterranean and South Africa. Regarding the oceanic whitetip shark Carcharhinus longimanus, age, growth and reproduction were elucidated in the Pacific Ocean for the first time and fundamental information on stocks of the shark was obtained.