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CHANGES IN FISH COMMUNITIES FOLLOWING CONCRETE LINING OF THE COACHELLA CANAL, SOUTHEASTERN CALIFORNIA GORDON MUELLER, GARY BRYANT and TOM BURKE Bureau of Reclamation Lower Colorado Region Boulder City, Nevada ABSTRACT ~~~ ~f, The fish community of a 3.4-km section of the concrete-lined Coachella Canal, Imperial County, California, was comprised of six species, with an absolute density of 0.039 fishlm2 and estimated biomass of 4.367 g/m2. When compared to studies conducts in the canal prior to lining, or in other unlined areas, these data suggest reductions in species diversity (-14.3 to -62.5%), density (+S~ to -X3.8%), and biomass (-30.1 to -91.2%). These data support speculations that numbers of river-adapted fish would remain relatively high in a concrete- lined canal, .but lentic and cover-oriented fishes such as centrarchids would decline. INTRODUCTION Water is an increasingly important commodity in the arid American southwest, and demands on this limited resource have placed important emphases on water conservation and salvage programs. Local, State, and Federal agencies are vigorously involved in identifying, developing, and implementing programs to better utilize existing water resources (Bureau of Reclamation 1984). Canal lining is a common, cost effective method of reducing seepage losses. In view of potential water shortages, efforts are being made to accelerate canal lining programs throughout the Imperial and Coachella Valleys of southern California. If these conservation programs are implemented, impacts of aquatic canal communities could be substantial. This paper presents new information concerning the fishery which reestablished following canal lining, and compares these data with those from investi- gations simultaneously conducted on an unlined portion of the same canal. Additional comparisons are made to studies conducted in two reaches of the Coachella Canal in November 1980, prior to lining (Minckley et al. 1983). STUDY AREA In 1980, the first 78 km of the Coachella Canal, southeastern California, were concrete lined as part of the Colorado River Basin Salinity Control Project, Title I. Our 1984 study site was a 3.4-km section of canal located approximately 13 km north of its diver- sion from the All-American Canal near Holtville, California (Fig. 1). The concrete canal has a ratio of 1.5:1 side-slopes, bottom width is 4.9 m, and top width is 16.3 m, with maximum water depth of 3.2 m. Maximum designed discharge capacity is 44 m31s with an operational water velocity of 1.4 mis. The same area was sampled in 1980, before lining (Minckley et al. 1983). METHODS To enable pre- and post-lining comparisons, sampl- ing techniques, location, season, and equipment were similar to those used by Minckley et al. (1983). The study area was subdivided into four sample sections (A, B, C, D, up- to downstream) ranging in length from 244 m to 1610 m. Each section was blocked by 2.5-cm bar-measure nets prior to water outage. Nets were Mueller, G., Bryant, G., and Burke, T. 1989. Changes in Fish Communities Following Concrete Lining of the Coachella Canal, Southeastern California. Journal of the Arizona-Nevada Academy of Science 23:1-6.