| Interstitial spaces between rocks (ISR) have an important function as an aquatic habitat, and a number of rehabilitations have been implemented using rocks of varying sizes in various countries. Although ISR as fish habitat have been relatively well studied in the natural streams, conventional survey methods are presumed inaccurate because they lack justification for the assumption that fish individuals were quantitatively caught. Furthermore, few studies have rigorously examined the relationship between fish assemblages and physical environment in ISR focusing on the varying sizes of rock. This study invented survey methods that quantitatively characterize the fish assemblages in ISR, and examined the relationships between fish assemblage and physical environment in ISR formed by rocks of varying sizes (100mm: pebble, 200mm: cobble, 350mm: boulder) in large experimental streams (800m long). Significant differences in fish assemblage structures were found only between pebble and boulder sites with species characterteristic of each rock size; the former with Japanese eel Anguilla japonica, goby Gymnogobius urotaenia and other demersal fishes and the latter with stone moroko Pseudorasbora parva, crucian carp Carassius sp. and other water-column fishes. The model analyses between each species and environmental variables (substrate size, velocity, depth, volume and light intensity in ISR) showed that velocity in ISR, channel velocity and depth contributed to fish uses of ISR, indicating that both micro habitat as ISR and channel condition were important determinants for fish habitat use. Our research suggests that effective rehabilitation using rocks would need to carefully consider both rock sizes and channel morphology condition. |
