Terms like "quite good," "the possibilities are promising" and "credible job of reflecting dynamic reality" sprinkle the latest scientific review of the statistical modeling tool used to choose federal Columbia/Snake river hydro operations that might best benefit migrating salmon and steelhead.

The Comprehensive Passage Model, called COMPASS, "is a welcome addition to the analytical tools available to both scientists and managers," according to the Independent Scientific Advisory Panel review made public Tuesday. It is the fourth in a series of ISAB reports issued as COMPASS was being developed by NOAA Fisheries Service in collaboration with federal, state, and tribal entities and the University of Washington.

The model is intended to predict the effects of alternative hydropower operations on salmon survival rates and provide ongoing evaluation of actual survival rates for the new Federal Columbia River Power System biological opinion. The BiOp, issued May 5, represents federal agencies' strategy over the next 10 years for assuring that hydro operations don't jeopardize the survival of 13 Columbia River basin salmon and steelhead stocks that are listed under the Endangered Species Act.

NOAA Fisheries on March 14 asked the science panel to review the most recent draft version of the COMPASS model. The 11-member board was formed in 1996 by the Northwest Power and Conservation Council and NOAA Fisheries to provide independent scientific advice and recommendations regarding scientific issues related to the agencies' fish and wildlife programs. In 2002, the Columbia River Basin Indian tribes were added as partners in the sponsorship of the ISAB.

NOAA's request posed a series of questions:

(1)Does the model successfully perform the desired capabilities, as listed below?

(a) realistically portray the hydro-system and variable river conditions;

(b) allow for the simulation of the effects of management;

(c) characterize uncertainty in prediction;

(d) represent hydro-system-related effects that occur outside the hydro system.

(2) Is the model too complex or too simple?

(3) Does the model realistically represent the data and its variability?

(4) Are the statistical methods sound?

(5) Is the documentation adequate?

The ISAB answered each, in most cases giving the biological model positive grades and offering suggestions for improvements.

"This critique is offered in the spirit of constructive suggestion to the COMPASS team, and we trust that our critique will be useful in continuing efforts to develop this valuable modeling tool for the region," according to the ISAB review's executive summary.

The review can be found online at:

http://www.nwcouncil.org/library/isab/isab2008-3.htm

"The point is that there's still work to do," said NOAA's Rich Zabel, who headed up the team. He said Tuesday he had had little time to look at the ISAB comments but at a glance they seemed to be generally favorable.

The purpose of the model "is to predict the effects of alternative operations of Snake and Columbia River dams on salmon survival rates, expressed both within the hydro system and latent effects which may occur outside the hydro system," according to a February review draft COMPASS manual.

Modeling for the BiOp focused on five interior basin "evolutionarily significant units" – stocks listed under the Endangered Species Act: Snake River spring/summer chinook salmon and steelhead, Upper Columbia River spring chinook and steelhead and Mid-Columbia River steelhead. The model was populated with the best empirically derived estimates of route-specific passage and survival rates available for juvenile chinook or steelhead to reflect the current configuration of the hydro system over a variety of annual water conditions – a 70-year record.

The model was used to assess the likely benefits of prospective actions that could be implemented under the new BiOp, which judges whether the hydro system jeopardizes the survival of listed stocks.

The COMPASS model has five modules: 1) reservoir survival, 2) dam passage and survival, 3) fish travel time, 4) hydrology, and 5) post-Bonneville survival.

"The model is supported by extensive data sets, particularly PIT-tag data, which provide information on survival and travel time," according to the draft COMPASS manual. "Additionally, dam passage parameters were estimated from radio-telemetry, acoustic tag, and hydroacoustic studies.

"The model was calibrated by fitting survival and migration rate relationships to historical data. During this calibration phase, we assembled historical data sets of river conditions (water flow, water temperature, and reservoir elevations) and dam operations (spill and transportation schedules), and we also implemented historical dam configurations."

COMPASS provides "alternative survival estimates for alternative operations" such as spill changes, transportation scheduling and flow and temperature conditions," Zabel said. It aims to gauge juvenile survival from dam to dam and through the available passage routes at the dam.

Changed dam configuration, such as the addition of spillway weirs, are also judged by COMPASS as to their effect on survival.

"Additional management scenarios that may be visited at a future time include reducing reservoir elevations to increase water velocity, predator removal, and dam breaching," the draft manual says.

The main purpose of the model is to compare hydro system survival across management scenarios but it will be used for a variety purposes, including in-season monitoring of survival and travel time to see if targets are being met.

It could possibly used in the future to help guide in-season management decisions, Zabel said.

COMPASS was used to assess smolt-to-adult returns of both transported and in-river migrating juveniles from the Bonneville dam tailrace, to the ocean, and back to the Lower Granite Dam for Snake River fish, or to Rock Island dam for Upper Columbia River fish.

The ISAB review was critical of the modelers attempt to "represent hydro-system-related effects that occur outside the hydro system."

"The Bonneville Dam -- Ocean -- BON survival component of the model is still poorly characterized, in the absence of reliable data from below Bonneville Dam. The ISAB's sense is that continuing to elaborate latent mortality is somewhat pointless, given the lack of comparable data from the pre-hydro-system period," the review says.

"The ISAB also concluded that it is time to separate the detailed survival experience of fish transported from each collection point (Lower Granite (DAM), Little Goose Dam (LGS), Lower Monumental Dam (LMO), and McNary Dam (MCN) separately, because those seem to be different, and it is not possible to model the transportation alternatives if transported fish from all four projects are treated as a single cohort."