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species such as smallmouth bass, and northern pike upstream of the structure, Channel catfish have a very large population in the Yampa and Colorado rivers, A well placed structure or weir has the potential to intercept migrating catfish and over time to deplete cattish populations upstream of the structure, Potential locations on the Yampa River could be near Echo Park or Deer Lodge, On the Colorado River a location would need to be determined based on spawning locations. For example, a weir at the 5th Street Bridge could deplete channel catfish in the] 5-Mile Reach, A dDwnstream trap might be effective fDr removal Dfsmallmouth bass Dr nDrthern pike, An analysis Dfthe nonnative fish that have been removed from the Gunnison River at the fish ladder cDuld provide an indicatiDn of potential impacts of a dam Dn Dther non-desirable species. Hypothesis 5, There is a strong inverse relationship between the size of the channel catfish and the size of round tail chub population, Observation: The largest population of round tail chub was at the Escalante site on the Gunnison River with a high number Df Age-O and Age-l fish collected, No channel cattish were collected in the GunnisDn River, The smallest populatiDn Df roundtail chub was at the Lily Park site on the Yampa River, which had a very large channel catfish pDpulation, It strongly appeared that habitat availability was not limited for roundtailchub at Lily Park. The 15-Mile reach was intermediate tD bDth the Escalante and the Lily Park sites fDr both roundtail chub and channel catfish, It was Dbserved in the IS-Mile Reach that the year with the highest percent composition of channel catfish (2003) was also the year with the lowest number of Age-O and Age-I roundtail chub in the sample. Roundtail chub were common in the Dolores River, a river with few channel catfish. This tendency suggests that channel catfish have had a negative impact on roundtail chub. HypDthesis 6a, Smallmouth bass recruitment is related tD temperature and warmer Summer and Fall temperatures since 2000 improved Age-O survival in the Yampa River. HypDthesis 6b, Release of COD I water frDm an enlarged Elkhead Reservoir could impact Age-O survival and small mouth-bass recruitment in the Yampa River. Observation: Smallmouth bass larger than 75 mm at the end of the grDwing season tend to have much better Dver-winter survival than smaller fish (Pat Martinez, persDnal cDmmunication). yay smallmDuth bass were abundant at Duffy in 1998 and 1999, but Dlder bass were not commDn, The increase in small mouth bass CDuld be a functiDn of wanner water temperatures during the dry years. A temperature modeling study appears warranted to determine the meri t of this hypDthesis, 44 I I I I I I I I I I I I I I I J 1 J I