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Table I . List of habitat types as classified by geomorphology. Secondary Channel (SeC) -habitats formed by the erosion/ deposition cycle of small secondary channels during passage of a flood, and revealed by receding water levels. Usually retaining slight flow until late in the year. Scour Channel (SC) -habitats formed by the erosion/deposition cycle of small channels behind large alternating sandbars. Scoured out during floods and revealed by receding water levels. Usually relatively deep and . permanent. Migrating Sand Waves (MS) -habitats formed by the relative movement of adjacent migrating sand waves. Relatively shallow and ephemeral. Horseshoe Vortex (HS) -habitats formed by scour holes generated at high flows at the upstream ends of islands due to development of horseshoe vortex patterns. Moderately deep and semi-permanent. Flood Plain (FP) -habitats formed by the inundation of abandoned channels or floodplains. Related to seasonal high flows or rainfall events. ~ Flooded Tributary Mouth (FT) -habitats formed by rising river levels flooding into tributary mouths. Related to seasonal high flows or rainfall events. Shoreline Eddy (SE) -habitats formed by recirculating areas due to irregularities of the bank. Constricted Reach Eddy (CE) -habitats formed by large eddies generated by constriction of the channel by ~ debris fans. Shoreline (SH) -shallow sloping shoreline areas. ~ RESULTS Species compositiou and relative abundance A total of 674,261 fish composed of 17 different species were collected during the study ~ period (Table A1). Five species were native, the remainder were non-native. The most common species collected were three non-native cyprinids; red shiner (Cyprinella lutrensis), sand shiner (Notropis stramineous) and fathead minnow (Pimephales promelas) (Table 2). These three species comprised an average of 79.8% of the total number of fish collected in the upper section, and 98.6% in the lower section. They were fairly evenly distributed, with red shiner most ~ abundant in 1992 and 1993, and sand shiner most abundant in the last three years. These three species are ubiquitous in the nursery habitats, and always occur together. For the remainder of this report they are collectively denoted asnon-native cyprinids (NNC). Other non-native species were collected sporadically and none made up a significant proportion of the total except in the upper section in the summer and fall of 1995, when mosquitofish (Gambusia aff nis) and ~ green sunfish (Lepomis cyanellus) occurred in greater abundance, presumably as a result of prolonged flooding of the Moab sloughs (Scott E. Matheson Wetlands Preserve), at RM 60 to 64. . 3