Early survival on Japanese flounder Paralichthys olivaceus and their recruitment mechanism: A review

To reveal some ecological factors determining the recruitment levels of Japanese flounder Paralichthys olivaceus, previous studies on factors affecting the early life history of flatfishes, such as quantitative fluctuations, developmental stages, and ecological conditions were reviewed. Many studies focused on the determining the effects of the timing of final settling of larvae and presence of settled first juvenile stages on year class abundances of juveniles after settlement associated with the drastic ecological changes of the metamorphic transition to the benthic stage. However, little quantitative information was available on the early survival of eggs and larvae of flatfishes that were present offshore and transported to the coast. Estimates from European plaice indicated that year class abundances of juveniles and yearly recruitment could be strongly affected by various factors, such as food availabilities on nursery grounds. Similar inferences to those described above have been found for Japanese flounder on the coasts of western Kyushu. Further, some studies suggested that mortality during the period of settlement would have a large impact on the total mortality in the early life stages of Japanese flounder. As results those analyzed by previously published data in the Northern Pacific, a significant positive correlation was found between mysid abundances and abundances of juvenile Japanese flounder. In addition, previously published data suggested that the yearly abundances of juvenile Japanese flounder were significant positively correlated to their recruitment in the Northern Pacific. Then it has been hypothesized that the number of larval and juvenile Japanese flounder individuals surviving during settlement is regulated by the mysid abundances. In the Northern Pacific, it has also been hypothesized that the strong year class strength is organized when successful transport on some great numbers of larvae Japanese flounder will be matched the occurrence of enormous mysid abundance on nursery grounds. Based on the integration of these knowledges, to examine survival strategies associated with the quantitative fluctuations of Japanese flounder in all over Japan, inspecting the significance of mysid abundance at settlement on the coast of western Kyushu was proposed.