摘要：Dams on rivers alter hydrology and geomorphology downstream, which often affect fish assemblage composition. Such was the case on the Upper Cheyenne River below Angostura Dam. Fish species composition varied dramatically among sampling periods, including pre-dam (1892 to 1893), immediate post-dam (1949 to 1952), and recent (post-1995) collections. Of 25 fish species that were collected, only the white sucker (Catostomus commersonii) was present in all sampling periods. Quantitative comparisons of recent samples (1996 to 1997 versus 2004) indicated 41% faunal turnover between 1997 and 2004 (seven species missing, two species gained). However, the most remarkable change from 1997 to 2004 was the increased dominance of red shiner (Cyprinella lutrensis lutrensis; from 6 to 22%) and smallmouth bass (Micropterus dolomieu; from 3 to 18%), and disappearance of flathead chub (Platygobio gracilis; from 28 to 0%). A mix of historic inhabitants, invasive native species, and invasive nonnative species dominated the recent (2004) fish community. Possible explanations for dramatic fish assemblage flux below Angostura Dam include variable sampling bias and gear limitations, major flow regime differences between drought periods and normal periods, top-down effects of smallmouth bass predation, chronic effects of Angostura Dam on instream habitat conditions, or (most likely) a combination of these effects.
