Population Dynamics and Connectivity Patterns of Adfluvial and Stream-Resident Cutthroat Trout

Information about population dynamics, life history variation, and connectivity patterns of threatened cutthroat trout (O. clarkii spp.) is critical for effective management and restoration. The Lahontan cutthroat trout (O. c. henshawi; LCT) is classified as threatened under the Endangered Species Act due to widespread extirpations across its range, and is at increased risk due to drought, habitat fragmentation, and climate change. This study was conducted in the Summit Lake Basin, NV (USA), which has a population of LCT that resides in Summit Lake and its tributary stream network. The objectives of this research were to (1) examine the population dynamics of stream- and lake-dwelling LCT in the context of drought, (2) quantify the amount of stream-resident versus adfluvial life histories in an adfluvial spawning tributary, and (3) identify the level of population connectivity between stream-resident and adfluvial components of the population. Chapter 1 shows that stream-dwelling trout were more resilient to drought disturbance and that drought refugia in the stream contribute to their resilience. Chapter 2 provides evidence for stream-residency in addition to high population connectivity across the lake and stream environments that is likely to increase in high flow years. While LCT and other cutthroat species have innate characteristics that allow them to persist in dynamic and harsh environments, this research highlights the importance of drought refugia and landscape connectivity to the long-term persistence and viability of co-occurring adfluvial and stream-resident fish