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. This study sought to the describe population dynamics of Burbot in the lentic portions of the Green River system and compare with Burbot population dynamics in 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 for fish in the Green River. Total annual mortality rates of Burbot were approximately 10% lower in reservoirs (33%) than for fish in the Green River. Additionally, lentic Burbot matured earlier than lotic Burbot. An age-structured population model indicated that Burbot populations were growing rapidly (λ = 1.18) in the study reservoirs. Annual exploitation of juvenile Burbot would need to reach 7%. Exploitation of 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 population growth rate. However, due to difficulties in collecting juvenile Burbot in the system, focusing removal effort on mature Burbot may be the most realistic option for suppressing Burbot populations in the Green River system.