PARENT SESSION
Poster Session 13: Landscape Ecology / Geomorphology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Spatial index for juvenile fish diversity in floodplain pools.

YAMASHITA, Shingo^*,1, ¹ River Restoration Team, Public Works Research Institute, Tukuba, Ibaraki, JAPAN

ABSTRACT- A predictive understanding of the relationship between biodiversity and the structure of the physical environment of floodplains is essential for the conservation of fish habitats and management of riverine environments. Floodplains contain numerous water-filled depressions called backwaters. Backwaters without permanent connection to the main stream, which are influenced strongly by annual floods, are referred to as floodplain pools in this study. Halyk and Balon (1983) showed that as nursery areas, floodplain pools produce fish biomass that can return to the stream during periods of stream-pool connection. They studied the relationship between fish diversity and pool area or stream accessibility during flooding, and found a significant correlation between species richness and pool area. However, no other parameters of the physical environment of floodplain pools were used in the study. Therefore, to explore predictors for juvenile fish diversity in floodplain pools, I investigated the relationship between species diversity and the spatial characteristics of pools on two scales (micro and pool scale). One major floodplain pool located in the middle reaches of the Chikuma River in central Japan was chosen for the micro-scale study. I measured the distribution of cyprinid juveniles and calculated eight spatial characteristics per 2-m grid cell in the pool on July 2000 and 2001. The regression tree models selected less distance from cover as the best predictor of the species richness of cyprinid juveniles during daytime. Ten floodplain pools located in the Chikuma River were chosen for the pool-scale study from October 2001 to July 2002. From the results of multiple linear regression analyses, the usefulness of two of thirteen geomorphological predictors, maximum depth and covered edge length, was demonstrated for the species richness of juvenile fishes. Maximum depth is considered to be an indicator of refuge function for juvenile fish from flooding. 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 parameters are not useful predictors, but the results of this study suggest the importance of habitat data on maximum depth and cover in predicting the function of nursery areas of floodplain pools.

Key words: Biodiversity, Floodplain pool, Geomorphology, Juvenile fish