Geographic Variation in Growth of the Starspotted Dogfish <i>Mustelus manazo</i> 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 vari ations in water temperature differed among localities. Great variations in maximum ages among locali ties 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). Fe males 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 sig nificant 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.

Reproductive biology of the fanray, Platyrhina sinensis (Batoidea: Platyrhinidae) in Ariake Bay, Japan

“…For some elasmobranchs, mating is correlated with minimum GSI, when the seminal vesicle is full of spermatozoa, and GSI reaches a low value (e.g., Yamaguchi et al 1997Yamaguchi et al , 2000Kyne and Bennett 2002). In also this study, males with mature sperm occurred from August to November when the monthly GSI was significantly decreased.…”

Geographic variation in the growth of white croaker, Pennahia argentata, off the coast of northwest Kyushu, Japan

“…In order to compare the growth equations between sexes or among localities, we followed the same procedure as Yamaguchi et al (1998). At first, we calculated the objective function (Y) of weighted least squares method, which is the residual sum of squares.…”

Occurrence, Growth and Food of Longheaded Eagle Ray, Aetobatus flagellum, in Ariake Sound, Kyushu, Japan

“…We used the x-radiography method for age determination, because it was most successful (Yamaguchi et al, 1998;Cailliet & Goldman 2004). We measured the radius of each centrum from the focus to the distal margin ( Figure 2).…”

“…The data was accepted if we counted the same number of rings every time. To determine the period of ring formation, we classified the marginal formation into three grades following methodology used in previous studies on sharks (Tanaka & Mizue 1979;Yamaguchi et al 1996Yamaguchi et al , 1998 Grade 1; A dark (opaque) ring has formed at the marginal region and is narrow, Grade 2; A light (translucent) ring has formed at the marginal region and is narrow, Grade 3; A light (translucent) ring has formed at the marginal region and is wide.…”