A Lota lota Consumption: Trophic Dynamics of Nonnative Burbot in a Valuable Sport Fishery

Abstract

Unintentional and illegal introductions of species disrupt food webs and threaten the success of managed sport fisheries. Although many populations of Burbot Lota lota are declining in the species’ native range, a nonnative population recently expanded into Flaming Gorge Reservoir (FGR), Wyoming–Utah, and threatens to disrupt predator–prey interactions within this popular sport fishery. To determine potential impacts on sport fishes, especially trophy Lake Trout Salvelinus namaycush, we assessed the relative abundance of Burbot and quantified the potential trophic or food web impacts of this population by using diet, stable isotope, and bioenergetic analyses. We did not detect a significant potential for food resource competition between Burbot and Lake Trout (Schoener’s overlap index = 0.13), but overall consumption by Burbot likely affects other sport fishes, as indicated by our analyses of trophic niche space. Diet analyses suggested that crayfish were important diet items across time (89.3% of prey by weight in autumn; 49.4% in winter) and across Burbot size-classes (small: 77.5% of prey by weight; medium: 76.6%; large: 39.7%). However, overall consumption by Burbot increases as water temperatures cool, and fish consumption by Burbot in FGR was observed to increase during winter. Specifically, large Burbot consumed more salmonids, and we estimated (bioenergetically) that up to 70% of growth occurred in late autumn and winter. Further, our population-wide consumption estimates indicated that Burbot could consume up to double the biomass of Rainbow Trout Oncorhynchus mykiss stocked annually (>1.3 × 10⁵ kg; >1 million individuals) into FGR. Overall, we provide some of the first information regarding Burbot trophic interactions outside of the species’ native range; these findings can help to inform the management of sport fisheries if Burbot range expansion occurs elsewhere.

Received March 18, 2016; accepted August 15, 2016 Published online October 14, 2016

ACKNOWLEDGMENTS

Our research was supported by UDWR Sportfish Research Grant 121041. We thank C. Walker and T. Hedrick for their technical assistance, and we are indebted to R. Mosley for considerable logistical support, FGR knowledge, and willingness to share data. R. Keith and C. Amadio (WGFD) assisted with the development and execution of this project, and A. Bonser provided angling expertise. C. Luecke provided supporting data for the manuscript. Additional support was provided by the U.S. Geological Survey, Utah Cooperative Fish and Wildlife Research Unit (in-kind) and The Ecology Center at Utah State University. J. Augspurger, M. Meier, M. Stephens, G. P. Thiede, B. Roholt, R. Walker, and B. Wegleitner provided additional assistance in the field and laboratory. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This study was performed under the auspices of Institutional Animal Care and Use Committee Protocol Number 1539, Utah State University.