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In 2004 native species comprised 53% of the total catch, less than in 2000 (81%) and 2001 <br />(65%) (Table 1). Black bullhead was the most common fish > 150 mm (44%) in 2004, but was <br />uncommon in 2000 (5%) and 2001 (0.6%). Anderson (2005) concluded that sedimentation <br />appeared to have increased suitable habitat for black bullhead and he further speculated that <br />predation by a large bullhead population could be responsible for the reduced flannelmouth <br />sucker and roundtail chub abundance in 2004. The Big Gypsum site is scheduled to be sampled <br />in 2005 (Anderson 2005). <br />Table 1, Species composition for fish >150 mm and total fish in sample. <br />Species <br />Composition Fish over 150 mm <br /> 2000 2001 2004 2000 <br />Flannelmouth 16 58 <br />sucker 2 10 <br />Bluehead 2 6 <br />sucker 1.2 1.0 <br />Roundtail 55 25 39 <br />chub 51 <br />Channel 16 8 6 <br />catfish 8 <br />Carp 3 1.7 7 1.7 <br />Green 2 1.4 <br />sunfish 4 <br />Brown trout 0.3 <br />Black 5 0.6 <br />bullhead 44 2.5 <br />Speckled <br />dace 18 <br />Red shiner 2.8 <br />Sand shiner 0.1 <br />Fathead <br />minnow 0.1 <br />Native <br />species 73.1 % 87.9% 42.9% 80.5% <br />The shift in species composition for flannelmouth sucker and roundtail chub between years <br />(2000 and 2001) was similar to Reach 5 data reported by Valdez et al (1992) for collections <br />made in 1990 and 1991. In 1990 the most common fish was roundtail chub (48%) followed by <br />flannelmouth sucker (35%), but in 1991 flamlelmouth sucker (51%) raid{ed first and roundtail <br />cub (20%) second. k7stability in species composition was not observed in other rivers with these <br />native species (Anderson 2004). The most likely explanation is these species are dominated by <br />young age-groups (Age 0 and Age 1) and minor changes in year class strength between years can <br />result in large variations in abundance between years. <br />16 <br />