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122 The Soulhu~eslern .Na(walisl vol. 28, no. 1 16 ~, 14 sT w 0 12 N C 10 O L T 8 .~. U C 6 a~ w 197 5 ° Log F = 4.81 Log TL-8.44 n=7 r2= 0,78 / • / •/ ~ O ~~ ~i O~M ~~ ~~ i // ~~ ~ •-----• 1976 i Log F=3.60 Log TL-5.4i i 4~ n= 17 r2= 0.57 0~, ~ ~ _ 300 350 400 450 500 Total Length (mm) Fig. 1.-Relation between fecundity and total length of bhtehead suckers Erom Echo Park, Yampa-Green rivers, 1975 and 1976. York, 1981). Fish as short as 79 mm were mature in the San Juan and Little Colorado rivers (Smith 1966). Data concerning size at maturity are somewhat biased in the present study because of collection F'^ nd re - - -a ,-i_-ar'- w.:h ...,...,..el ...., ,.nd as a^result, large individuals comprised most of the collection rColorado and Gunnison river colle- tions were made with electrofishing gear in addition to trammel nets, and a more representative sample was probably obtained. However, large individuals still dominated the collections. fiish examined in this study produced [ewer eggs than bluehead suckers examined by other investigators. Smith (1966) estimated a 319 mm standard length bluehead sucker from the Green River contained 8,500 eggs. A Eish of equal length Erom the Yampa or Green rivers would have produced 5,450 eggs in 1975 or 5,050 eggs in 1976, based on our regression equations. A fish o[ equal length from the Colorado or Gunnison rivers would have produced 7,760 eggs. The esti- mated average fecundity Eor bluehead suckers from the Weber River, Utah (n = 4, 380 to 440 mm TL; Andreasen and Barnes 1975) was 20,227, which is considerably greater than estimated by us. Diameters of mature ova Erom fish examined in the present study were similar to those from the Weber River (1.5.5 ro 2.25; Andreasen and Barnes 1975). Fecundity of [lannelmouth suckers (Calostomus latipinnis) also is greater in the Colorado River than in the Green and Yampa rivers (vlcAda, M.S. thesis, Utah State Univ., Logan. 105 pp., 1971). The greater fecundity may be anributable to temperature differences between the two areas. Temperawre of the Green River is affected by Flaming Gorge Dam (approximately 105 ktn upstream from Echo Park), and is 5-15° lower than that of the Colorado in summer (at the two collection sites; LLS. Geological Survey, Water Resour. Div., Salt Lake City, various pagination, !96!-75).