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. , C) , (.:-) ~ ~~. ~, ~ en ~ co ~ ~ ~ , , , , , ~ , -, '" -, ~ :l :l ~ :l ) .~ ") ~ :i :i ~ ) '"' ~ ? ? '"' ~ '" ~ '" .. '" .. '"' ~ '"' -# '" -# '"' ~ ... ~ " ~ Fish species common in summer collections were also common in autumn collections. Plains killifish and western mosquito fish were generally more common in autumn than summer collections. Between 1993 and 1995 total autumn abundance of fishes (Reaches combined) did not change appreciably. Total abundance in 1996 (a low spring runoff and summer flow year) was substantially less than in preceding years. In 1997, total abundance was the lowest ofthe study. From 1993 through 1996, Shannon- Wiener Diversity declined but increased in 1997 to the second-highest value of the study. Total abundance of fishes in Reach 5 peaked in 1993 and 1996 and was lowest in 1997. Between 1993 and 1995, Shannon-Wiener Diversity changed little, declince in 1996, and was highest in 1997. Red shiner was the most abundant species in autumn collections in Reach 5 in all years, except 1997 (high spring runoff and summer flows) when speckled dace was most abundant. Fathead minnow and specked dace were usually the second- or third-most common species. Flannelmouth sucker and bluehead sucker were rare in 1996, a low spring runoff and summer flow year. Colorado pikeminnow, likely stocked individuals, was the third-most common species in Reach 5 secondary channels in 1997. Roundtail chub was found only in 1997. No attribute of summer discharge was significantly related to any commonly-collected species, except the positive relationship between autumn abundance of western mosquitofish and days discharge < 500 cfs. Attributes indicative oflow summer flow were negatively related to autumn abundance of native species. Mean summer discharge was negatively related to red shiner abundance. Between 1993 and 1996, total abundance of fishes in Reach 4 declined slightly, but abundance in 1997 was considerably less than in preceding years. Shannon- Wiener Diversity changed little from 1993 through 1996 and increased slightly in 1997. Red shiner was the most abundant species in all years and fathead minnow or speckled dace were second-most abundant in all years. Neither flannelmouth sucker nor blue head sucker was common during autumn in Reach 4 secondary channels and bluehead sucker was absent in 1996. Colorado pikeminnow and roundtail chub were found in Reach 4 secondary channels in 1997, but not in preceding years. Elevated summer flows were negatively correlated with summer abundance of nonnative red shiner, fathead minnow, channel catfish (significantly) and western mosquito fish; fathead minnow abundance was significantly, and positively, related to days summer discharge < 500 cfs. Autumn abundance of native flannelmouth sucker, bluehead sucker, and speckled dace were negatively, but not significantly, related to days summer discharge < 500 cfs. Total abundance of fishes in Reach 3 peaked in 1995 and was least in 1997. ShannOn-Wiener Diversity declined from 1993 through 1996, but increased in 1997. Red shiner was always the most abundant species in Reach 3 and fathead minnow or speckled dace were always second- or third-most common, except in 1993 when channel catfish was third- most common. Flannelmouth sucker was uncommon in all years and bluehead sucker was absent in 1993. Colorado pikeminnow and roundtail chub were found in 1997. No attribute of summer discharge was significantly related to autumn abundance of any commonly collected species. Speckled dace abundance Was negatively related to days discharge < 500 cfs. . . In most years (1993 through 1997), summer abundance of fishes was usually greater in summer than autumn; in Reaches 5 and 4 differences were substantial. Between summer and autumn (years combined) abundance differences were typically . iii