Identifying demographic uncertainties & vulnerabilities in an invasive Smallmouth Bass population: Implications for reservoir management & mechanical removal efforts

Authors: Lindsey Bruckerhoff, Charles Yackulic, Drew Eppehimer, Kevin Bestgen

Year: 2022

Abstract

We developed a population model for Smallmouth Bass (Micropterus dolomieu) in the middle Green River of the upper Colorado River basin. This model can be used to compare population responses of M. dolomieu to future environmental variation and management scenarios. Developing a tool to identify and compare management strategies to control M. dolomieu is a priority because the species is considered a top threat to the recovery of federally listed fish species in the Upper Colorado River basin. The model integrates long-term M. dolomieu catch-effort data, abundance estimates, and early life history data and links interannual variability in demographic rates to environmental conditions in two river reaches. We used the model to identify and compare drivers of M. dolomieu population change, including hydrology, river temperature, exploitation, and immigration, and quantify uncertainty associated in these drivers. We determined there is substantial uncertainty regarding the extent to which population dynamics in the middle Green River are driven by immigration from the Yampa River and tributary reservoirs versus local recruitment. This uncertainty, in turn, makes it difficult to identify how effective management, including reducing age 0 survival and removing all size classes, needs to be to create meaningful, long-term reductions in abundance of M. dolomieu. Integrating additional data and learning from application of ongoing experimental management efforts could reduce this uncertainty over the coming years.