| Between 2003 and 2005、 we investigated fish fauna in 25 Ishikari River oxbow lakes where a similar survey was conducted in 1977. The results showed a significant increase in the number of fish species、 many of which were invasive species. Cluster analysis of the patterns of change revealed three groups: 1. Small number of species: a significantly increased species count、 around half of which consisted of invasive species; 2. Average number of species: an increased species count、 around 2/3 of which consisted of invasive species; 3. Large number of species: a slightly increased species count、 around half of which consisted of invasive species. Compared to the situation in 1977、 the similarity among fish species tended to be significantly higher. These results indicate that fish fauna increased and became more homogenous over the 28-year period、 and that the uniqueness of fish communities was lost. The influence of invasive species was also clarified. |
