Heredia, N. and P. Budy. 2018. Trophic ecology of Lahontan Cutthroat Trout Oncorhynchus Clarkii Henshawi: historical predator-prey interaction supports native apex predator in unique desert lake. Transactions of the American Fisheries Society. 147:842–854, DOI: 10.1002/tafs.1006. USGS FSP: IP-066465.
Pyramid Lake, Nevada remains one of the last strongholds for lacustrine Lahontan cutthroat trout (Oncorhynchus clarkii henshawi; LCT), following historical declines throughout their native range. In Pyramid Lake, LCT have persisted despite anthropogenic alterations, and the population now depends entirely on stocking programs and efficient management. The purpose of this study was to identify important food-web interactions and potential limitations to the LCT population. The objectives were to 1) compare seasonal depth distributions, seasonal diet overlap, and trophic niche overlap between LCT and non-native Sacramento perch (Archoplites interruptus); and 2) to evaluate the seasonal depth distribution patterns of LCT and native tui chub (Gila bicolor), seasonal changes in LCT diet, and current LCT trophic position (TP). LCT remain apex predators, with both trophic position (large LCT TP = 4.30 ± 0.04 [mean±1.96∙SE]) and diet composition indicating high rates of piscivory (average annual rate of piscivory = 77.1% for large LCT; > 400 mm TL) throughout the year. Small LCT (200 – 400 mm TL) exhibited weak dietary overlap (Schoener’s Index = 0.55) and large LCT exhibited strong overlap (0.72) with Sacramento perch. Small and large LCT, and Sacramento perch, preyed most heavily on tui chub. Isotope data indicates strong overlap between large LCT and Sacramento perch niche space (large LCT 88.6%); however, catch rates indicate that Sacramento perch are only present in small numbers throughout the lake. LCT demonstrate high rates of piscivory, are not negatively influenced by the presence of Sacramento perch and do not appear to be exceeding carrying-capacity.