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Abstract

Nonnative rainbow trout (Oncorhynchus mykiss) are stocked into several reservoirs in the range of federally threatened Little Colorado spinedace (Lepidomeda vittata), and so have the opportunity to negatively impact Little Colorado spinedace populations. We examined rainbow trout escapement from Nelson Reservior into Nutrioso Creek, critical habitat for L. vittata. We also examined movements of L. vittata and incidence of predation by rainbow trout on L. vittata. We detected no movement of rainbow trout out of Nelson Reservoir over 4 years of study. Lepidomeda vittata marked in 3 streams did not move much; but sample sizes were too small to make any meaningful conclusions regarding movement. Most L. vittata we captured during surveys subsequent to marking were unmarked, suggesting movement out of the study area, low tag retention, mortality, or failure to capture marked fish. Lepidomeda vittata co-occurred with O. mykiss, Salmo trutta, and Salvelinus fontinalis and were typically less than half the size of the sympatric nonnative salmonids. Consequently, they are potential prey fish for these species. We found fish remains in stomachs of 33% of S. trutta, 6% of O. mykiss and 25% of S. fontinalis examined, but remains of L. vittata were found only in a single S. trutta. Because S. fontinalis are rare in the streams examined, they probably do not pose a great threat to L. vittata. Salmo trutta, which are no longer stocked, had the highest piscivory level and may thus pose more of a threat to L. vittata than O. mykiss.

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