USING FLUVIAL GEOMORPHOLOGY TO DESIGN SUCCESSFUL HABITAT FEATURES

The Rio Grande silvery minnow (Hybognathus amarus) is an endangered fish species in the Rio Grande, NM. A dramatic decline in minnow population was noted after the Army Corps of Engineers Cochiti dam began operating in 1973; Cochiti dam was built for flood and sediment retention. The dam is located approximately 45 miles north of Albuquerque NM forming the upstream end of the middle Rio Grande reach. The decreased peak flows and sediment supply initiated changes in channel morphology linked with degraded fish habitat. Successful recovery of this species is dependent on both identifying suitable habitat features and then recreating the features (restoration). One difficulty in designing habitat restoration projects for riverine fish species is translating quantitative habitat measurements into a functional landscape. Since the silvery minnow produces semi-buoyant pelagic eggs, examining the minnow?s early life history in the context of fluvial geomorphology suggests that nursery habitat is lacking in the river. Identifying nursery habitats (microhabitat features) begins by finding and quantifying where the eggs and larvae exit the main current for rearing (retention). A geographic information system (GIS) is used to visualize geomorphic data coupled with fishery data for evaluating physical associations with the declining silvery minnow populations. Understanding the relationships between channel morphology and microhabitat will provide fishery and watershed managers better tools for directing habitat restoration, and other activities for species recovery.