This is a long-standing, well-run project that attempts to sustain the South Fork Snake River's native Yellowstone cutthroat trout (YCT). The sponsors are to be commended for the quality of the proposal and the success of their work to date.

1. Purpose: Significance to Regional Programs, Technical Background, and Objectives

The South Fork Snake River is one of the last strongholds for fluvial Yellowstone cutthroat trout within their historical range, and it provides an important fishery with significant economic value. There is a clear need to maintain the viability of this population which is currently threatened by, among other factors, hybridization and competition with non-native rainbow trout and by entrainment in a large irrigation diversion called the Great Feeder Diversion. The purpose of the proposed work is to minimize hybridization of Yellowstone cutthroat trout and rainbow trout, and to quantitatively assess entrainment and subsequent mortality of cutthroat trout in the large irrigation diversion system (an ISRP recommendation), which will result in development of best management practices to minimize entrainment and mortality. 

The sponsors provide a nice description of the situation and a clear definition of the problem. The sponsors provide strong justification for this work, first, by clearly discussing the nature of the threats posed by hybridization and competition with rainbow trout and the dangers to the population of large scale entrainment, and second, by demonstrating how the proposed work fits into their overall management strategy for protecting viability of Yellowstone cutthroat trout in the South Fork Snake. The steps that are being taken to address these problems are well reasoned and carefully planned and, if successful, should lead to major benefits for the fish population. Unlike some other waters in the Columbia River Basin where threats from non-native fishes are so severe that they probably have no hope of a satisfactory outcome, the South Fork Snake offers the opportunity to provide significant benefits to native fish with continued work. The proposed work is consistent with the Fish and Wildlife Program and the Upper Snake Subbasin Plan.

There are two objectives: to protect the genetic integrity and long-term viability of the Yellowstone cutthroat trout population in the South Fork Snake River and to increase the survival rate of the cutthroat trout population in the South Fork Snake River. Both seem appropriate and important. A major assumption of the proposed work is that removal of rainbow trout is critical for cutthroat trout recovery, and another is that this can be accomplished. The sponsors make the case that "yes" applies to both, and the ISRP agrees.

2. History: Accomplishments, Results, and Adaptive Management (ISRP Review of Results)

The history of the project and changes in the fish population over the past decade show the ability of the sponsors to recognize the problem, to target and conduct specific research to define alternatives, and implement a multi-pronged management approach. The accomplishments presented in the proposal are operational changes that involve modifications to the weirs in each of the cutthroat trout spawning tributaries which should significantly improve capture of fish migrating into the tributaries. This is important because it allows the sponsors to remove rainbow trout and hybrids and so lessen their chances of their spawning with Yellowstone cutthroat trout. However, this discussion, by only dealing with operational improvements to weirs, does not provide a full understanding of the breadth of accomplishments of this project.

Adaptive management is shown in many ways, especially regarding screening of the tributaries. In fact, the entire management program for Yellowstone cutthroat trout in the South Fork Snake has been evolving based on past results of the work. The changes instituted include weir modifications undertaken because previous weir designs were ineffective, establishment of an angler incentive program to reduce densities of rainbow trout and hybrids in the mainstem South Fork Snake, and modifications to flow regimes regulated by Palisades Dam to benefit cutthroat and the riparian ecosystem.

ISRP Retrospective Evaluation of Results

This project can claim substantive accomplishments that have progressively improved management of Yellowstone cutthroat trout in the South Fork Snake River. The sponsors have a clear understanding of the major problems facing cutthroat trout in the South Fork and have taken steps to address these problems that are well-reasoned and carefully planned and, if successful, should lead to major benefits for the fish population. Their three-pronged approach for managing cutthroat trout includes establishing a more natural flow regime, minimizing competition and hybridization with non-native rainbow trout, and reducing entrainment in irrigation diversions. One of the greatest challenges facing this program at present is measuring entrainment of trout in a major diversion, the Great Feeder, and developing best management practices to reduce entrainment rate. This is a difficult problem to address, but it is necessary for reduction of entrainment mortality. Not all of their work is funded by BPA, but the BPA-funded portion is key and integrates well with their overall management plan.

3. Project Relationships, Emerging Limiting Factors, and Tailored Questions for Type of Work (hatchery, RME, tagging)

Relationships between the proposed work and other South Fork Snake activities involving federal agencies and non-governmental groups are well described. It is also evident how the proposed work complements other IDFG actions designed to bolster cutthroat trout by managing the fishery.

Pertaining to emerging limiting factors, the sponsors obviously are addressing the problem of non-native species. They also provided a thorough discussion of the possible impacts of climate change on Yellowstone cutthroat trout and how their management practices could lessen these impacts.

4. Deliverables, Work Elements, Metrics, and Methods

Three deliverables pertain to the tributary work and three address the Great Feeder entrainment component. They appear to be important and clearly described, with appropriate methods, and most appear accomplishable using the approaches and methods outlined in the proposal. Deliverables 4 and 5, which pertain to quantification of entrainment of cutthroat trout in the Great Feeder Diversion and its subsidiary canals, are the most uncertain, but nevertheless necessary. This problem admittedly is difficult to address and the sponsors propose a complex design that involves multiple methods of sampling, extensive PIT tagging, and multiple detection sites. It would have been helpful if the sponsors had discussed how entrainment rates will be calculated for the Great Feeder and subsidiary canals using PIT tag data.

The sponsors state in Deliverable 4, “The estimate of previously PIT tagged cutthroat trout entrained through the Great Feeder will be compared to the estimate of PIT tagged cutthroat trout in the entire South Fork Snake River drainage to gauge the population-level impact of entrainment at the Great Feeder Diversion.” This is a desirable, even critical, estimate. The sponsors, however, needed to clearly explain how they will obtain an estimate of the number of PIT-tagged fish in the entire drainage and why they believe this is the appropriate way to measure proportion entrainment. Perhaps a more appropriate measure would be the number of fish entrained relative to the number of fish passing the entrainment site over any given time period, not the total number of fish in the river. With continued sampling of entrained fish and fish passing the entrainment site throughout the time period when river flow is diverted, a seasonal estimate of entrainment proportion could be obtained. Admittedly, these measurements would be difficult to obtain.

Genetic “sorting” appears to be based on visual identification of rainbow trout and rainbow-cutthroat hybrids. While this is a pragmatic approach, it will likely result in an underestimation of the contribution of rainbow genes into the cutthroat trout population. Unfortunately, alternatives that provide greater discrimination are not practical for real time management.