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April 1985 MCADA, WYDOSKI: FLANNELMOUTH SUCKER 283 TABLE 1. Length-weight, body-scale and length-fecundity relationships for flannelmouth stickers from the Gunnison, Colorado, Green, and Yampa rivers, 1975-1976. LENGTH-WEIGHT Yampa/Green: Log W = 3.13 Log TL - 5.37 (n = 297, R2 = 0.9) Colorado/Gunnison: Log W = 3.09 Log TL - 5.21 (n = 292, R2 = 0.9) BODY-SCALE Yampa/Green Rivers Male: TL = -18.6342 + 4.8894 SR - 0.0054 SR2 - 0.0004 SR3 (n = 139, R2 = 0.9) Female: TL = -8.7835 + 3.5187 SR + 0.0131 SR2 - 0.0001 SR3 (n = 137, R2 = 0.8) Colorado/ Gunnison Rivers Male: TL = -8.7835 + 2.9904 SR + 0.0156 SR2 - 0.0001 SR3 (n = 158, R2 = 0.8) Female: TL = 46.385 + 0.2820 SR + 0.0443 SR2 - 0.0002 SR3 (n = 137, R2 = 0.8) LENGTH-FECUNDITY Yampa/Green: Log F = 4.03 Log TL - 6.70 (n = 58, R2 = 0.6) Colorado: Log F = 3.00 Log TL - 3.76 (n = 45, R2 = 0.7) Gunnison: Log F = 3.48 Log TL - 5.14 (n = 15, R2 = 0.6) were counted. The fecundity of that fish was then estimated by proportion using total ova- ry weight. Total counts of ova from two fish demonstrated that estimated fecundity dif- fered from actual fecundity by less than 5%. The mean diameter of mature ova from indi- vidual fish was derived from measurements of 30 ova made with an ocular micrometer. The total length-fecundity relationships were de- termined using the equation Log F = b, Log TL - bo (Bagenal 1967), where F is fecundity and bo and bI are empirical constants derived using least-squares analysis. Statistical comparisons between length- weight, body-scale, and length-fecundity regression equations were made using analy- sis of covariance (Snedecor and Cochran 1967). this report (Fig. 2). Average growth in- crements of all fish were greatest at the for- mation of the third annulus and declined steadily thereafter. Data for the two sexes were combined be- cause there was no significant difference be- tween the length-weight relationships for male and female flannelmouth suckers (P>0.05). No statistical difference was de- tected between length-weight regressions from data on fish from the Gunnison and Col- orado rivers (P>0.05). Flannelmouth suckers from the Colorado and Gunnison rivers were significantly heavier than fish of equal length from the Yampa and Green rivers (P<0.001: Table 1). Reproduction RESULTS Age and Growth About 80% of the flannelmouth suckers used in our analyses were collected between April and July. The collection from the Gun- nison River was made in April 1976. Body- scale relationships differed significantly be- tween male and female fish among the study areas (P<0.05: Table 1). However, mean length at annulus formation was similar for the study groups and they were averaged for In the Colorado and Gunnison River col- lections, the smallest mature female was 421 mm long, and all females longer than 490 mm were mature. The smallest mature male was 391 mm long, and all males 470 mm or longer from the Colorado and Gunnison riv- ers were mature. In the Yampa and Green River collections, the smallest mature male was 393 mm long, and all males were mature at 460 mm: the smallest mature female was 405 mm long and all females were mature at 470 mm (Table 2). Thus, fish began to mature at age IV and most were mature by age VI.