Abstract
An undescribed goby, Rhinogobius sp. BI (Bonin island type) sensu Suzuki (1992), is now endangered, however, there is little information about their micro-distribution and the habitats which are necessary for their conservation. Field research on Chichi-jima and Haha-jima islands in the Northwestern Pacific was done twice to clarify the present status of the goby populations. The presence of the goby was confirmed at all the stations in the south area of Chichi-jima Island and at four stations of Haha-jima Island. The goby inhabited deep water in streams with sand and gravel, and the population density was assessed to be comparatively high at Tokoyono-taki and Shigure-dam. The specimens collected from Haha-jima Island well matched R. sp. BI from Chichi-jima Island. But, the variation about the numbers of pectoral fin rays and predorsal scales, is low in the specimens from Haha-jima Island. The population of Haha-jima island seems to have low genetic diversity as compared with that of Chihi-jima island. Present study suggests that each population composes an independent local population.
