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a <br />ISSUE 1, 1989 CHANGES ^V FISH COMMUNITIES FOLLOWING CONCRETE LINING OF THE COACHELLA CANAL <br />Information collected in 1980 (Minckley et al. 1983), <br />prior to lining the first 78 km of the Coachella Canal <br />(Reach I), allows for a comparison offish communities <br />on a pre- versus post-project basis. Additional infor- <br />mation, available from studies made during the same <br />dewaterings in 1980 and 1984 but conducted 100 km <br />further downstream (Reach II) (Beaty et al. 1981, <br />Beaty 1984), provide somewhat of an experimental <br />control (Table 3). <br />Comparisons of fish diversity (number of species), <br />density (fishlm2), and biomass (grams/m2, Table 4) <br />demonstrate that, in nearly all instances, values for the <br />lined canal are lower than those in earthen sections. <br />The only exception was a slight increase in fish den- <br />sity (8.9%) when compared to Beaty's 1984 data. Even <br />with that increase, overall biomass dropped more than <br />30%. The data suggest that concrete lining led to <br />changes in species diversities of -14.3 to -62.5%, den- <br />Table 3. Comparison of the Relative Abundance (%) of Major Fishes Taken from Lined and Unlined Sections <br />of the Coachella Canal. <br /> Reach I <br />Pre-lining <br />1980 <br />(Minckley et al. <br />1983) <br />Post-lining <br />1984 <br />1980 <br />(Beaty et al. Reach II <br />1984 <br />1981) (Beaty 1984) <br />Channel catfish 78.8 96.6 83.3 86.1 <br />Threadfin shad 0.2 1.1 0.3 0.0 <br />C~'p 1.0 1.0 0.3 4.9 1! <br />Red shiner 11.5 1.2 0.0 2/ 1.2 <br />Largemouth bass 2.6 Tr. 31 2.2 1.9 <br />Sunfish 5.1 0.0 1.1 3.5 <br />Flathead catfish 0.9 0.0 1.1 2.4 <br />Tilapia 0.0 Tr. 11.2 0.0 <br />Black crappie 0.0 0.0 Tr. 0,0 <br />Striped bass 0.0 0.0 0.0 0.1 <br />Total 3,527 3,439 4,714 1,092 <br />fishlm2 0.229 0.089 0.147 0.034 <br />g/m2 49,369 4.367 12.035 6.245 <br />1/ =sample included five experimental grass carp (Ctenopharyngodon idellus) <br />2/ =not included in analysis. <br />3/ = Tr. less than 0.05 percent. <br />sities of +8.9 to -83.8%, and biomass of -30.1 to <br />-92.2%. <br />These declines undoubtedly reflect corresponding <br />reductions in the type and diversity of aquatic habitat. <br />As predicted by Minckley et al. (1983), fishes adapted <br />for swiftly flowing water continued to maintain rela- <br />tively high populations. Conversely, those fishes <br />dependent upon cover and more lentic conditions were <br />signficantly reduced or eliminated. For example, <br />largemouth bass, other centrarchids, and flathead cat- <br />fish (Pylodictis olivaris) contributed 7.9 to 15.6% to the <br />earthen canal's total community. In the lined canal a <br />single largemouth bass was the only fish to represent <br />that group (0.035%). <br />Changes in relative abundance were less obvious. <br />Channel catfish remained the dominant species. <br />Catfish in the earthen section represented 78.8 to 86.1% <br />of the total catch compared to %.6% for the lined canal. <br />Although the earthen canal enjoyed a greater degree <br />of species diversity, the majority of species contributed <br />a small portion of the overall community. <br />While the above comparisons assume that Reach II <br />data provide an experimental control, it must be <br />recognized that the relatively low values for 1984 could <br />also be the impact of either the upstream, lined section <br />of the canal, or of maintenance activities. Regardless, <br />trends in either case (i.e., valid or invalid 1984 control) <br />suggest decreases in diversity density, and biomass <br />after lining. <br />The first, 78-km, lined section of the Coachella <br />Canal represents a relatively short section compared <br />to the entire canal system in southern California. <br />