Geographic Variation in Growth of the Starspotted Dogfish Mustelus manazo from Five Localities in Japan and Taiwan

Abstract

Geographic variations in growth of the starspotted dogfish Mustelus manazo from five localities off Japan and Taiwan were examined from centrum analysis using soft x-radiography. Based upon seasonal centrum edge analysis, dark rings were formed annually, during the period of June and July in all localities. It was suggested that ring formation did not vary among localities, although seasonal variations in water temperature differed among localities. Great variations in maximum ages among localities were found. The differences in maximum ages between the northernmost population, Aomori, and southernmost population, Taiwan, were almost two times for both sexes (male, 5-9; female, 9-17). Females grew to a larger size than males and were apparently longer-lived in all localities. The significant sexual differences in growth were found in Maizuru and Shimonoseki. For both sexes, Aomori was the largest length at each estimated age in five localities, and Taiwan was the smallest. The growth differed in all localities for males and most localities for females significantly, however, for females, no significant differences between Tokyo Bay and Shimonoseki, and Tokyo Bay and Taiwan were found. The specimens tended to grow larger and have longer life span in the eastern and northern areas, however, the water temperature may not be a major factor for differences in growth.