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...-: r ~", ~.... ,< ,16 J-)e-JIL/U I <t- -- "'.'r'Dp~+ J (..1 '6'0 / ~ 070C;( /D / 1':" ; 'I !, IV ,.'fer'/-< 'JI'teJr"f" I - ( ))\. .""" .---- RED SHINER VS. NATIVE FISHES: REPLACEMENT OR DISPLACEMENT? Kevin R. Bestgen Department of Biology University of New Mexico Albuquerque, New Mexico 87131 and David L. Propst New Mexico Department of Game and Fish State Capitol Santa Fe, New Mexico 87503 ABSTRACT The introduced red shiner, Notropis lutrensis, has been implicated with reductions in the range and abundance of fishes native to southwestern desert streams. Non-overlapping distributions of red shiner and federally threatened Gila River endemics, Meda fulgida and Tiaroga cobitis, are thought to be evidence of competitive interactions resulting in historic reductions in range and abundance of these two native forms. A recent range expansion of red shiner into the Gila River of New Mexico and complementary distribution of red shiner and native cyprinids was documented, but does not indicate that competitive interactions are occurring. Habitat degradation, reduction in streamflow, and high summer water temperatures in the Gila River below the Middle Box supressed native fishes prior to invasion of red shiner and allow'ed this fish to colonize and dominate the community. In the Gila River above the Middle Box, abundant populations of native fishes including threatened forms exist, and despite a colonization date similar to that in the lower river, red shiner constitutes less than 1% of the community. Analogous situations in th_ San Francisco River, NM and the Verde River, AZ suggest that a transition zone exists. In its native range, red shiners are most abundant following reductions of other indigenous forms caused by habitat degradation. Thus, abundant, diverse indigenous faunas appear to inhibit establishment of large populations of red shiner. The red shiner appears to merely fill voids in Gila River fish communities caused by prior habitat degradation. Maintenance of permanent streamflow and pristine habitat are critical to sustain native fishes and supress populations of red shiner. D~~ rl ~ ~k s CI~YV f'JC~J \rUl \~)'9t~ II