Budy, P., G.P. Thiede, N. Heredia, and Erik Horgen. 2021. Exploring the contemporary relationship between predator and prey in a significant, remnant Lahontan Cutthroat Trout population in Pyramid Lake, Nevada. Submitted to the Transactions of the America Fisheries Society. DOI: 10.1002/tafs.10291
USGS FSP: IP-119395.
Lahontan Cutthroat Trout (LCT) Oncorhynchus clarkii henshawi have experienced some of the most marked reductions in abundance and distribution of Cutthroat Trout. In Pyramid Lake, Nevada, USA the population of LCT has returned from the brink of extirpation, and although highly managed via stocking, is thriving, and has recently started to reproduce naturally. Our objectives were to determine: 1) if predator and prey remain tightly coupled, 2) whether LCT are food limited, and 3) the status of the LCT population with regard to the potential prey-based contemporary carrying capacity. We used a multi-faceted approach including intensive field fish sampling, bioenergetic modeling, cohort reconstruction, and comparisons of prey availability to consumption. We estimated the average population of LCT in Pyramid Lake is 1.2 million, average annual stocking is 650,000, and fish angled ranges from 5,000 – 14,000/yr (90% release rate). Driven by seasonal and size variation in consumption, individual annual consumption of LCT varied from 667 - 992 g/yr for small LCT (200 – 400 mm) and 2,388 - 3,057 g/yr for large LCT (> 400 mm). LCT are consuming on average, 14 – 63% of the standing crop of Tui Chub Gila bicolor annually, indicating that LCT are currently not exceeding their prey-based carrying capacity. LCT in Pyramid Lake remain tightly coupled to their primary native prey, Tui Chub, despite considerable changes to the ecosystem. This means managing for a robust population of LCT translates largely to managing for forage fish. This supply versus demand issue is a particular concern in Pyramid Lake given there is indication the density of Tui Chub is declining concordant with declining lake elevation. Given the conservation importance of this population of LCT, careful monitoring is critical; however “predation inertia” indicates effective short-term management in response to fluctuations in forage fishes is likely possible.