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,... i~ Ii \ . }t 330 BIOLOGICAL REroRT 19 ,; ., Silver chubs were known only in the Missouri River into southeastern South Dakota, and speckled chubs were not known to occur north of Nebraska. Pflieger (1975) considered speckled chubs common in the Missouri and lower Mississippi rivers. Stur- geon chubs, sicklefin chubs, flathead chubs, and silver chubs were considered common inhabitants of the Missouri River and the Mississippi River downstream from the Missouri confluence (Pflieger 1975). However, Pflieger and Grace (1987) reported a dramatic decline in the abundance of flathead chubs from 1940 to 1983 throughout the Missouri River in Missouri. Although they reported slight increases in the density of sturgeon chubs, sicklefin chubs, silver chubs, and speckled chubs in Mis- souri, these species were only numerous in the lowermost sections ofthe Missouri River nearest to the Mississippi River. Upper stations on the Mis- souri River in Missouri and adjacent to Nebraska showed low numbers of these chubs in 1978-83 collections (Pflieger and Grace 1987). During 1971, 1974, and 1975, 16,384 small fish were seined during 3,060 seine hauls with a 150m bag seine (6.13-mm mesh) from the channelized Missouri River in east-central and southeast Ne- braska (Hesse and Wallace 1976). No sturgeon chubs or sicklefin chubs were collected; 324 (2.00Al by composition) flathead chubs, 1,195 (7.3%) silver chubs, and 72 (0.4%) speckled chubs were collected (Table 1). From 1986 to 1990, 6,217 small fish were seined (234 seine hauls, 150m bag seine, 6.13-mm mesh) from the channelized Missouri River in east- ',' I ~I ~1 i;! '~' ,~ ~' r central and southeast Nebraska. One sicklefin chub and 1 sturgeon chub (0.03%), 3 (0.05%) flathead chubs, 120 (1.90/0) silver chubs, and 2 (0.03%) speck- led chubs were collected. Mean catches per seine haul were as follows: flathead chubs, 0.11 (1971- 75) and 0.01 (1986-91); silver chubs, 0.39 (1971-75) andO.51 (1986-91); speckled chubs, 0.02 (1971-75) and 0.009 (1986-91). Seine hauls were difficult to replicate; percent composition is a better indicator of population trend than CPUE in this instance. Two reaches (165 km) of the Missouri River in northeast Nebraska remain unchannelized, al- though the uppermost reach (72 km) is isolated between Fort Randall and Gavins Point dams. During 1983-90, 32,448 small fish were seined (1,360 hauls, 15-m bag seine, 6. 13-mm mesh). No sturgeon chubs, sicklefin chubs, or speckled chubs were collected; one (0.003%, 0.OOO7jhaul) flathead chub, and seven (0.02%, 0.005jhaul) silver chubs were collected. River Minnows in the Missouri River Plains minnows (Hybognathus placitus) and the western silvery minnows (H. argyritis) were com- mon in the Missouri River at the turn of the cen- tury. They are similar species taxonomically and with respect to habitat preferences (Pflieger 1975). Jones (1963) reported they were widely distributed in the Platte, Republican, Loup, Elkhorn, and Nio- brara rivers. The plains minnow was the most abundant minnow in the upper Missouri River in Table L The relative abundance and catch per unit of effort (CPUE) of flathead chubs, silver chubs, speckled chubs, plains and silvery minnows combined, and total cyprinids seined from the Missouri River, Nebraska. Species Location Period Effort No. sampled Sample size % CPUE Flathead chubs channelized 1971-75 3,060 324 16,384 2.0 0.11 channeliied 1986-90 234 3 6,217 0.05 0.01 unchannelized 1983-90 1,360 1 32,448 0.003 0.0007 Silver chubs channelized 1971-75 3,060 1,195 16,384 7.3 0.39 channelized 1986-90 234 120 6.217 1.9 0.51 unchannelized 1983-90 1,360 7 32,448 0.02 0.005 Speckled chubs channelized 1971-75 3,060 72. 16,384 0.4 0.02 channelized 1986-90 234 2 6,217 0.03 0.009 unchannelized 1983-90 1,360 0 32,448 0.0 0.0 Plains and silvery minnows channelized 1971-75 3,060 4,589 16,384 28.0 '1.5 channelized 1986-90 234 102 6,217 1.6 0.4 unchannelized 1983-90 1,360 21 32,448 0.06 0.01 Total cyprinids channelized 1971-75 3,060 6,180 16,384 37.7 2.01 channelized 1986-90 234 229 6,217 3.7 0.9 unchannelized 1983-90 1,360 28 32,448 0.09 0.02