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function of a lack of smaller fish there, instead of a lack of larger fish on the Colorado River. Mean lengths between all sites were statistically different at P<O.OOI in 1999. Duffy in 1999 also had the highest percent oflarger roundtail chub with 90% of the sample 40 cm or larger, a result of very few chub under 40 cm. At Sevens 67% of the chub were 40 cm or larger, but on the Colorado River only 4% were in over 40 cm (Appendix C Figure 7, 8 and 9). Mean length of roundtail chub on the Colorado River was 321 rom and 449 mm and 400 mm for Duffy and Sevens, respectively (Table 4.), and mean lengths between all sites were statistically different at P<O.OOI in 1999. The smaller mean length on the Colorado River for Chub is due to a much better representation of smaller sized fish, Table 4. Mean length for fish >15 cm collected in the Yampa and Colorado Rivers. MEAN LENGTH IN MM -. Sevens Sevens Duffy Duffy 15-Mile Species/year 1998 1999 1998 1999 1999 BH 342 336 357 382 366 CC 497 448 529 476 433 CP 572 533 670 679 440 CPM 628 610 608 575 573 FM 488 465 . 459 486 422 NP 383 411 433 518 RTC 380 400 442 449 321 5MB 295 276 278 292 WB . 329 375 413 421 374 WF 460 442 475 473 393 WS 359 352 411 406 287 Duffy also had significantly higher mean lengths for most other species including catfish, carp, white sucker and white-flannel mouth and white::bluehea,d hybrids, pike and bass ". .- ~'~aTi ~ (Table 6). On the Colorado River small white sucker were found primarily in backwater habitats whereas white sucker over 25 cm were primarily in the main channel (Appendix C Figure 10 and 11). The smallest channel catfish caught on the Yampa River was 30 cm and 34