Abstract
All life stages of the largescale sucker (Castostomus macrocheilus) occurred throughout the Hanford Reach of the Columbia River. Peak population estimates were 14,961 + 9422 and 12,343 + 6721 per km for June and July 1981. Although some individuals showed little movement, tag-return data indicated the majority of the population was mobile. Most upstream movement over Priest Rapids Dam occurred in June. Growth rates, as determined by analysis of scales, were highest during the 1st 4 years and ranged from 37-73 mm per year until maturity. Fish were aged to 15 years, however measurements of tagged fish provided evidence that ages of larger fish were underestimated. Length-weight relationships were logeW = -9.8 + 2.7 logeL and logeW = -5.8 + 2.0 logeL, for females and males, respectively. Both sexes matured near 400 mm FL at 6-9 years of age. Peak spawning occurred in late May and June at water temperatures from 12-15 C. Anal fin length of mature males was significantly larger than mature females throughout the year. Diet of largescale sucker consisted mainly of periphyton and insect larvae. Diet overlap occurs between sympatric bridgelip sucker (C. columbianus) and several members of the cyprinid community at Hanford. Largescale suckers are important prey for a number of vertebrate predators, including fishes and birds.
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