KATOH, M.; Seikai Natl. Fisheries Res. Inst., Okinawa: Migration rates of commercially important demersal fishes (Lethrinus atkinsoni and Lethrinus nebulosus) between coral reef islands in Okinawa, Japan

The family of Lethrinidae includes many important food species, and about 900 tons (including some lutjanid species) are harvested annually in the vicinity of coral reefs in Okinawa. Two of the most abundant species (Lethrinus atkinsoni and Lethrinus nebulosus) made up more than half of the total catch. L. atkinsoni and other species are known to aggregate for spawning. This behavior makes them a good target for fishing. The annual catch of Lethrinidae has decreased recently. Knowledge of the population structures and migration rates of commercially important fish species is necessary for effective resource management. There have been few studies that focus on the population structures of coral reef fishes in the vicinity of the Ryukyu Islands. About 50 individuals per population of L. atkinsoni and L. nebulosus were collected around Okinawa, Miyako and Ishigaki islands, which are ca. 300 and 150 km apart, and around Okinawa and Ishigaki islands, respectively. Allele frequencies of six polymorphic allozyme loci for L. atkinsoni and of four for L. nebulosus were investigated. Maximum-likelihood estimation of migration rates using a coalescent method indicated that higher migration rates towards the southwest direction, which is against the major Kuroshio Current. Gene flow along counter currents seems to be predominant for lethrinids in Okinawa. These results and migration estimates from regular F_st values will be compared.