Date of Award

6-2009

Department/Program

Natural Resources Management

Advisor

James R. Vilkitis

Abstract

This study examined the diet composition of ninety-nine Sacramento pikeminnow (150-410 mm [5.9-16 in] fork length [FL]) collected from the upper and lower main stem of Chorro Creek, Morro Bay Watershed, California in 2006. The goal of this study was to characterize the spatial and seasonal variability in the diet of Sacramento pikeminnow within Chorro Creek and to determine what proportion of the diet is represented by rainbow trout (Oncorhynchus mykiss) and their anadromous form (steelhead). Prey was identified in 88% of the samples collected in the early season and 84% of the samples collected in the late season. Fish and/or scales were identified in 12% of the samples collected. Sacramento pikeminnow consumed a wide variety of prey; the diversity of individual diets was higher in the lower main stem than the upper. Overall, diet diversity increased with Sacramento pikeminnow length. In both the early and late season, crayfish formed the largest part of the diet of large Sacramento pikeminnow (>250 mm [9.8 in]). There was a slight increase in the proportion of fish in the diet during the late season, and tendency for cannibalism which was primarily observed in the upper main stem of Chorro Creek. In summary, the overall results of this study support the conclusion that Sacramento pikeminnow are not significant predators of O. mykiss in natural stream conditions. However, conclusions about the ability of Sacramento pikeminnow in Chorro Creek to reduce O. mykiss populations will require further information on the prey selection of Sacramento pikeminnow when juvenile O. mykiss and adult pikeminnow are abundant.

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