Dr. Lisa Eby writes about her resarch in conjunction with undergrad student Ryan Kovach on trout population dynamics in the Gros Ventre River, Wyoming.
"The Gros Ventre River historically provided spawning and rearing habitat for native Snake River fine-spotted cutthroat, including resident fish that live in the Gros Ventre year-round and migratory fish that move between the Gros Ventre and the Snake River systems. Principal threats to the Gros Ventre native trout include both impediments to movement (water diversions which result in loss of both water and fish into irrigation ditches) and the presence of non-native trout. Seasonally the lower section of the Gros Ventre River is dewatered impeding movement between the Snake River and Gros Ventre and reducing fish habitat. We are working in collaboration with Grand Teton National Park, Trout Unlimited, Gregory Aquatics, Wyoming Game and Fish, and several landowners to better understand these threats and be able to evaluate management alternatives.
We are quantifying the loss of juvenile and adult fish into irrigation diversions along the Lower Gros Ventre and examining the potential population level implications associated with these diverted fish. To examine what fish are in the ditches, we are electrofishing in irrigation diversions to assess the species and size found in the ditches. In addition, we are using trap nets and passive integrated transponder (PIT) tags with detection devices placed at locations near headgates to examine entrainment in and movement through the irrigation diversions.
 Another critical issue involves non-native rainbow and cuttbow hybrid trout. We are sampling the Lower Gros Ventre to examine the magnitude and extent of rainbow trout and cuttbow hybrid trout. These fish may create both genetic and ecological factors limiting the native cutthroat population. We are collecting fish through electrofishing and hook and line to collect genetic samples in the Gros Ventre and surrounding area. A UM undergraduate student, Ryan Kovach, is working on this project to examine the extent to which these species have been interbreeding in the river. With several collaborators (Trout Unlimited and Gregory Aquatics) we will combine the results of genetics with fish use and movement data to examine how these different groups of fish use the resource. For example, we will be able to look at whether pure cutthroat, hybrid cutthroat, and rainbow trout use in the same habitat and migrate at the same time.
We need to better understand these issues to better develop and evaluate management options. For example, the Gros Ventre is currently isolated from the Snake River during much of the summer. Depending on the extent of this problem, retaining more water in the Gros Ventre may help keep these populations connected. The connection to the large Snake River system could be detrimental to the genetically pure population of cutthroat trout found in the main Snake River system. The research efforts will fill key uncertainties for future discussions and help identify options for native trout restoration."
|