Abstract
To explore predictors for juvenile fish diversity in floodplain pools during a low-water period, we surveyed the relationship between species richness and geomorphological characteristics of floodplain pools. Ten floodplain pools located in the middle reaches of the Chikuma River were chosen for this study. These pools were formed by a flood in September 2001. We surveyed each pool from October 2001 to July 2002. The data at the end of October was used for analysis of the period after flooding in autumn. The data at the end of March 2002 was used for analysis of the period before next flooding in spring. Species richness of juvenile fish was used as the target variable. Thirteen geomorphological parameters of each floodplain pool were measured: area, perimeter, covered edge length, proportion of covered edge length to total perimeter, maximum depth, average depth, coefficient of variation of depth, substrate diversity, length of pool, width of pool, shape index, distance from stream, and distance from nearest pool. From the results of multiple linear regression analyses, the usefulness of two of thirteen geomorphological predictors, maximum depth and substrate diversity, was demonstrated for the species richness of juvenile fishes after flooding in autumn. At the period before flooding in spring, the usefulness of proportion of covered edge length to total perimeter was shown. Maximum depth is considered to be an indicator of refuge function for juvenile fish from flooding. Substrate diversity is assumed the index of habitat heterogeneity of floodplain pools. It appears that the presence of cover is a requirement of juvenile fish for feeding and refuge. Because the number of pools in this study was small (n = 10), only these three parameters are not useful predictors, but the results of this study suggest the importance of habitat data on maximum depth, substrate diversity, and cover in predicting the function of nursery areas of floodplain pools.
