Invasive Lake Trout Reproduction in Yellowstone Lake under an Active Suppression Program

Abstract

In Yellowstone Lake, predation by invasive Lake Trout Salvelinus namaycush has caused significant abundance declines in native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. Lake Trout suppression has been ongoing since 1995; assessment and simulation modeling are used to measure suppression effectiveness and guide efforts. Lake Trout reproduction demographics are linked to these modeling efforts via quantification of the population stock-recruitment relationship. To improve estimation of this relationship for Lake Trout in Yellowstone Lake, we assessed reproduction demographics by quantifying spawning periodicity, size at maturity, and female fecundity. Histological assessment suggested that females with a gonadosomatic index (GSI) >3.0 and males with a GSI >1.0 were capable of spawning. Approximately 65% of mature females appeared to have spawned on an annual cycle. In 2015, the mean absolute and relative fecundities were 4,612 eggs and 1,535 eggs/kg, respectively; temporal differences in relative fecundity (1996, 2006, 2007, and 2015) were not statistically significant. Lake Trout population fecundity has declined from a peak in 2010 due to reduction in abundance of spawners. The estimated population fecundity of approximately 4.7 million eggs in 2020 represents an 81% decline from the mean estimate of previous samples and an 87% reduction from peak population fecundity. Despite declines in population fecundity, age-2 recruitment has increased in recent years; our results suggest these increases are not related to changes in reproductive demographics, but rather are related to increased prerecruitment survival. Our results provide information for understanding temporal variation in spawning stock biomass of Lake Trout in Yellowstone Lake and the capacity of the population to

Fish carcass deposition to suppress invasive lake trout through hypoxia causes limited, non‐target effects on benthic invertebrates in Yellowstone Lake

“…This extensive suppression effort has reduced adult lake trout abundance by >80% since 2012; however, recruitment of young lake trout remains high (Koel, Arnold, et al, 2020). The lake trout spawn from late September to early October (Heredia et al, 2021) at sites characterized primarily by cobble and bedrock substrate; confirmed lake trout spawning sites range in size from 0.3 to 2.0 ha and comprise 0.03% of the total area of Yellowstone Lake . To curtail lake trout recruitment and improve suppression efficiency, the NPS has developed a novel method that deposits carcasses directly on spawning areas in the littoral zone of the lake to induce decomposition and cause mortality in lake trout embryos via oxygen depletion (Poole et al, 2020;Thomas et al, 2019).…”