銚子産ホシザメの年齢,成長,繁殖および食性について

抄録

Over 400 specimens of Mustelus manazo were collected from Choshi to study its age, growth, reproduction, and food habits. Annuli were estimated to occur on vertebral centra yearly from analysis of monthly marginal growth ratios. linear relations were obtained between radius of centrum and total body length. Von Bertalanffy growth equations are described as follows; male: l_t=1043[1-exp{-0.19(t+2.00)}]: famale: l_t=2771[1-exp{-0.032(t+4.77)}]. Both males and females reached their first maturity at 621-640mm and all the specimens over 700mm attained their maturity. However, age determination suggests that females reached maturity at a little older age than males. Monthly gonad indices of males show that copulation occurred between June and July. Gestation period is estimated to be approximately 10 months. Litter size ranged from 1 to 22 with an average of 4.9, although litter size increased with the length of the parent. Stomach content analysis shows that Crustacea were the most important prey animals with 85% occurrence. Among others, percentage occurrence of crabs exceeded 50%. Fishes composed chiefly of sardine were also important food items as well as Polychaeta and Spinculoidea.