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<br />Table 3, Density estimates at Duffy, Yampa River 1998 to 2003
<br />
<br />YAMPA RIVER Density estimate in fish per hectare
<br />DUFFY Nolha no/ha Nolha Nolha nolha
<br />Species 1998 1999 2000 2001 2003
<br />Total fish 62,9 65.6 51,5 69,4 40,0
<br />Flannelmouth sucker 4.0 2.4 1,8 0,7 0,9
<br />Bluehead sucker 3,6 3.7 4,0 2,7 0.5
<br />Colorado pikeminnow 1.3 0,9 0.6 0.5 0,0
<br />Roundtail chub 2.8 2,9 1,8 2,6 1,1
<br />White S, + hybrids 39.2 39,4 33,0 29.7 20,8
<br />Channel catfish 2,6 5,5 2.3 3.9 3,0
<br />Carp 1,8 1.5 0,5 1,3 0,2
<br />Smallmouth bass 5,0 6.3 6,7 27,1 13.0
<br />Northern pike 2.5 3,0 0,6 1,0 0.5
<br />
<br />Biomass estimates were much lower in 2003 for nearly ail species compared to the
<br />baseline years (Table 4), White sucker and their hybrids were the dominant taxon at this site
<br />over the study period. This species was the best indicator of biomass potential. The large
<br />drop in white-hybrid sucker biomass indicated the fish population was negatively impacted
<br />by the flows in 2003, Bluehead sucker biomass was very low (0.2 kglha) in 2003. The
<br />species that displayed the least change in biomass in 2003 compared to baseline years were
<br />channd catfish and smailmouth bass,
<br />
<br />Table 4. Biomass estimates at Duffy, Yampa River 1998 to 2003,
<br />
<br />YAMPA RIVER
<br />Duffv Kg/ha Kg/ha Kg/ha Kg/ha Kg/ha
<br />Species 1998 1999 2000 2001 2003
<br />Total fish 66,5 65,9 51,0 47.4 22,6
<br />Flannelmouth sucker 4,7 2.7 2,2 0,8 1,1
<br />Bluehead sucker 1.8 1,3 2,2 1,5 0,2
<br />Roundtail chub 2,5 2,7 1,6 22 1.1
<br />Colorado pikem',nnow 2,5 1,6 0,9 0,7 0
<br />White S. + hybrids 39,9 39.7 35 26.9 12,7
<br />Channel catfish 4,3 6,5 3,3 4,1 3,9
<br />Carp 7,3 6,1 2.8 6,1 1,5
<br />Smalimouth bass 1,9 2,6 2,3 4.8 1,9
<br />Northern pike 1.5 2,8 0,7 0,2 0,3
<br />
<br />Mean length of white sucker and smallmouth bass was less in 2003 compared to the
<br />baseline years (Table 5), This higher presence of Age-I white sucker and small mouth bass in
<br />the 2003 sample (Figures A] - 19 and AI-51) indicated improved survival of Age-O in 2002.
<br />This could be due to relaxed predation on their young-of-year (yay) during 2002. Age-l
<br />bluehead sucker, flannel mouth sucker or roundtail chub were not observed in the 2003
<br />survey (Figures A 1-2, A 1-9 and A 1-14) suggesting their yay had poor survival rates in
<br />2002. Also both Age-O and Age-I carp were not found at Duffy in 2003 (Figure A 1-39),
<br />
<br />17
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