Andrus, C. W. Dynamac Corporation Environmental Services, andrusc@mail.cor.epa.gov
Greene, M. C. Dynamac Corporation Environmental Services, greenem@mail.cor.epa.gov

 
COMPARISONS OF SUMMER FISH ASSEMBLAGES BETWEEN OFF-CHANNEL AND MAIN CHANNEL HABITATS OF THE WILLAMETTE RIVER, OREGON, USA.
 
Fish assemblages in off-channel features of a large river in the Pacific Northwest were sampled in summer, 1997, to determine differences between daytime and nighttime use of these habitats. Certain species and size classes of fish migrated from the main channel at night; this was most pronounced for large grazing species such as largescale sucker (Catostomus macrocheilus) and chiselmouth (Acrocheilus alutaceus). Physical features and water characteristics influenced, to some extent, relative abundance and size classes of fish among and within off-channel features. Fish were sampled at night within paired off-channel and main channel sites in summer, 1998, to determine spatial patterns and habitat associations throughout a 70-km reach of the river. In addition, a subset of these sites were sampled twice again to investigate temporal changes from early to late summer. Main channel fish assemblages were predominantly larger fish. Their relative abundance and species mix exhibited complex longitudinal changes from upper portions of the study reach to lower portions. Off-channel features were dominated by smaller fish and these assemblages were often influenced by physical and water characteristics. Introduced fish were present in small numbers within off-channel features and rarely found in the main channel. Fish within off-channel features had a greater percentage of physical anomalies than did fish in the main channel.
 
Day: Monday, Feb. 1
Time: 02:45 - 03:00pm
Location: Hilton of Santa Fe
 
Code: SS47MO0245H