Environmental conditions and fish faunas in low elevation rivers on the irrigated san joaquin valley floor california usa

Saiki, M.K.

California Fish and Game 70(3): 145-157


ISSN/ISBN: 0008-1078
Accession: 005368375

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Physical and chemical characteristics of the lower San Joaquin and Merced rivers showed longitudinal (upstream to downstream) patterns related primarily to irrigation activities. Turbidity, total alkalinity, conductivity, and concentrations of macronutrients (NH3-N, NO3 + NO2-N, total N, ortho-PO4, and total P) increased conspicuously at downstream sampling sites. The fish fauna also differed at upstream and downstream sites. Species captured primarily at upstream sites were sculpins, Cottus spp.; green sunfish, Lepomis cyanellus; redear sunfish, L. microlophus; Sacramento squawfish, Ptychoceilus grandis; hardhead, Mylopharodon conocephalus; and threespine stickleback, Gasterosteus aculeatus; species that seemed to be restricted to downstream sites were inland silverside, Menidia beryllina; white crappie, Pomoxis annularis; threadfin shad, Dorosoma petenense; fathead minnow, Pimephales promelas; splittail, Pogonichthys macrolepidotus; Sacramento blackfish, Orthodon microlepidotus; tule perch, Hysterocapus traski; and striped bass, Morone saxatilis. Published information on the general habitat requirements of fishes indicates that environmental changes are probably influencing the composition and abundance of fish faunas. Further research is needed to isolate the direct and indirect effects of environmental contaminants on fish, with particular emphasis on identifying the toxic components of irrigation return flows.