Population characteristics and management of lentic populations of nonnative Burbot in the Green River system, Wyoming.
Fishes introduced outside of their native distributions have the potential to negatively affect their recipient ecosystems. Since their illegal introduction into the Green River, Wyoming, in the 1990s, Burbot Lota lota have been sampled in lotic and lentic environments throughout the Green River system, where they pose a threat to native fishes and valuable sport fisheries. In response to this invasion, managers of the Green River have begun to explore the efficacy of a suppression effort targeting Burbot. We sought to the describe population dynamics of Burbot in the lentic portions (i.e., reservoirs) of the Green River system in comparison with Burbot population dynamics in lotic areas of the Green River. We also sought to evaluate potential management scenarios for a suppression program. Burbot for this study were collected from Fontenelle and Flaming Gorge reservoirs in October and November 2016. Growth rates of Burbot in the lentic portion of the system were higher than those for fish in the Green River. Total annual mortality rates (A) of Burbot were approximately 10% lower in the reservoirs (33%) than in the Green River. Additionally, lentic Burbot matured earlier than lotic Burbot. An age-structured population model indicated that Burbot populations were growing rapidly (population growth rate λ=1.18) in the study reservoirs. Annual exploitation (µ) of juvenile Burbot would need to reach 7%; the µof mature Burbot would need to increase to 33% or greater (A ≥57%) to effectively suppress Burbot in this system. Sensitivity analysis suggested that mortality of age-1 and age-2 Burbot had the greatest influence on λ. However, due to difficulties in collecting juvenile Burbot in the Green River system, focusing removal efforts on mature individuals may be the most realistic option for suppressing Burbot populations in this system.