Geographic Variations in Reproductive Parameters of the Starspotted Dogfish, Mustelus manazo, from Five Localities in Japan and in Taiwan

Abstract

Geographic variations in reproductive parameters of Mustelus manazo from five localities, four in Japan (Aomori, Tokyo Bay, Maizuru, and Shimonoseki) and one in Taiwan, were investigated from November 1994 to June 1996. Differences in age and length at sexual maturity from Aomori to Taiwan were approximately 3 years and 300 mm in TL, respectively, for both sexes. The sharks appeared to mature at a later age and to a larger size in the most northern population, Aomori, and to be faster and smaller in the southern population, Taiwan. Mating, ovulation and fertilization periods were generally during May and August in the four localities of Tokyo Bay, Maizuru, Shimonoseki, and Taiwan. In Aomori, males showed no clear monthly variation in gonad index, and females in Aomori had a protracted reproductive period. Females became pregnant every year in all localities, except Aomori. The Aomori population apparently has a different reproductive cycle. The Tokyo Bay population is distinctive regarding growth and sex ratios of embryos. In all localities, the number of embryos per litter increased relative to total length of mother. There was no geographic variation in reproductive parameters between Maizuru and Shimonoseki. The coast between these last two sampling areas is a continuous steep slope with similar environmental conditions, and mixing of the two populations may occur.