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NW Fishletter #378 February 5, 2018

[3] Capacity Metric Can Quantify Habitat Benefits, Idaho Experts Say

Editor's note: This story marks the last NW Fishletter piece from Laura Berg, who retired in December. We appreciate her many contributions as our fish reporter, and wish her all the best in retirement. Her successor, K.C. Mehaffey, started with us on Feb. 5.

Idaho scientists say they have a promising new method for prioritizing habitat-restoration actions and evaluating their contribution to salmon and steelhead recovery.

The new approach, described at a Northwest Power and Conservation Council meeting in November, could be a breakthrough for salmon managers and project funders who have been frustrated by the difficulty of demonstrating, quantitatively, whether habitat actions are achieving regional goals, including delisting goals.

In fact, U.S. District Judge Michael Simon, in rejecting the 2008-2014 BiOp on the Federal Columbia River Power System, said the BiOp and its reasonable and prudent alternatives (RPAs) relied too heavily on uncertain benefits from habitat-improvement projects.

The new approach--integrated rehabilitation assessment (IRA) being used in Idaho's Salmon River subbasin--was explained to Council members by Mike Edmondson, Idaho Offices of Species Conservation; Chris Beasley, Quantitative Consultants; Jude Trapani, Bureau of Reclamation; and Mark Davidson, The Nature Conservancy.

IRA uses a life-stage, habitat carrying-capacity metric that sequentially identifies and targets the most limiting life stages of salmonids. It employs a machine-learning technique called quantile random forest (QRF) to estimate the available capacity.

This approach and similar recent habitat initiatives in the region contrast with past approaches that isolated habitat limiting factors and tried to fix them without distinguishing the fish life stages affected.

To determine if a particular stream or reach has capacity to support salmonids at particular life stages, IRA uses data and analyses from two BPA-funded efforts-integrated status and effectiveness monitoring program (ISEMP) and Columbia habitat monitoring program (CHaMP).

PIT-tag antennae being installed in Lemhi River, Idaho. Credit: Milstein/BPA

ISEMP and CHaMP use various sampling and identification techniques, including in-stream PIT-tag detection systems, to estimate adult and juvenile fish abundance and life stage-specific growth and survival.

These programs have come under extra scrutiny because of high costs and the difficulty of ascertaining their value to salmon recovery.

While the Council is requiring modifications to the two habitat-monitoring programs, their potential importance to habitat restoration in the region is highlighted by the Idaho work.

Modeling the data using QRF allows linking stream quantity and quality data with fish life-stage survival, which in turn permits estimating habitat capacity.

To determine how much habitat capacity is needed to improve salmon and steelhead abundance, IRA defines regional goals on the basis of habitat-capacity requirements for different life stages.

For instance, if a goal for a particular tributary is 2,000 adult fish, that number of adult fish requires 980 redds, or spawning areas, which requires 1.5 million parr (fish stage between fry and smolt) to emerge from the redds, which in turn requires 700,000 parr to survive to the pre-smolt life stage.

Because QRF can estimate how much a proposed rehabilitation action is likely to increase survival and habitat capacity, it can be used to prioritize prospective projects.

For example, although data might suggest that one rehabilitation project would increase a stream's capacity significantly more than another, if IRA indicates that spawning habitat for redds is not currently limiting capacity, it would place projects to improve spawning habitat at a low priority.

A completed restoration project also can be evaluated on how much it has increased survival at critical life stages and how much that contributes to achieving population goals.

Such calculations will help salmon managers and project funders estimate the amount of rehabilitation necessary to achieve life-stage recovery goals and identify the best opportunities for restoration actions.

In the future, the Idaho scientists predicted, the QRF approach will be able to compare existing and proposed modeling results to inform project-engineering design.

Using IRA methods, measuring progress toward goals can be completed faster and more cost-effectively than the standard monitoring and evaluation metric can be replicated in other interior Columbia River Basin watersheds, the scientists said.

They also said the new metric would use existing information with no or very limited new data necessary, with the possible exception of the Clearwater River watershed in the Snake River Basin.

This would lower the costs of monitoring and evaluation, one of the more expensive items in the Columbia Basin Fish and Wildlife Program.

And, importantly, new approaches like IRA can help pick the projects most likely to increase salmon and steelhead survival in the basin, which is what the road to recovery is all about, they said. -Laura Berg

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