Change in Distribution of Bitterlings, and Effects of Urbanization on Populations of Bitterlings and Unionid Mussels in Tatara River System, Kyushu, Japan

The populations of Japanese bitterlings and unionid mussels and the land use of the watershed were investigated in 36 sampling sites in the Tatara river system in northern Kyushu, Japan. Five bitterling species were found in 11 sites in the system. Although Rhodeus ocellatus kurumeus was found to be distributed in 23 sites in 1983, this species was found in three sites in this study. The population of the bitterlings decreased in the sites with a high urbanization rate, although the populations of several other fish species showed no dependence on the urbanization rate. The population of the mussels showed a negative correlation with urbanization rate. In addition, the mussels populations showed positive relationship with the bitterling populations. These three relationships indicate that the decrease in the bitterling population due to the urbanization of the watershed was responsible for the decrease in the mussel population.