Age and growth of marbled sole Pleuronectoes yokohomae in Kikonai Bay, Hokkaido, Japan
Age and growth of marbled sole Pleuronectes yokohamae werer estimated from growth increments in otolith. The samples were collected with commercial set nets and an experimental bottom trawl net in Kikonai Bay and the nearby waters, southern coast of Hokkaido, from May 1994 to July 1995. Monthly changes in the percentage occurrence of oltoliths with translucent edge in one band and the marginal increments on the other hand verified that the translucent zone was formed once a year after their spawning season in May, indicating availability of outer margin of translucent zone as an annulus. The regression method as well as Fraser-Lee's method was used to estimate the back-calculated lengths. Growth of marbled sole was expressed by the von Bertalanffy asymptotic growth function: TLt=361.78[1-exp-0.390(t-0.098)) for males and TLt=438.15[1-exp-0.323(t-0.145)) for females using back-calculated lengths by the regression method and TLt=367.04[1-exp-0.388(t-0.114))] for males and TLt=436.05[1-exp-0.323(t-0.147)) for females by the Fraser-Lee's method, where TLt is total length (millimeters) at estimated age t. The theoretical lengths predicted by these two methods at all estimated ages were very similar. It was found that the growth rate of marbled sole in this study area was relatively high compared to those obtained in the Inland Sea of Japan as. However, the highest growth rate was observed with regard to the population off Fukushima Prefecture, although the bottom water temperatures were similar to those in Kikonai Bay. It is inferred that the geographical variation in the growth rates of marbled sole is influenced by the hydrographic and food conditions.