The recently released draft environmental impact statement for Columbia River System Operations found that, out of six alternatives, Snake River salmon and steelhead would have the highest predicted smolt-to-adult returns (SARs) under an alternative that would breach the four lower Snake River dams and increase spill to 120 percent total dissolved gas at four lower Columbia River dams.
But a seventh alternative—not included in the draft EIS, but analyzed in the 2019 Comparative Survival Study—offers even higher percentages of returns for Snake River fish, according to the analysis.
The Fish Passage Center hosted its annual meeting on the Comparative Survival Study (CSS) by webinar on April 17, with 10 presentations on the 2019 study. Scientists went over conclusions from several of the study's topics, including juvenile survival and a review of the literature on delayed mortality.
The webinar concluded with results of the salmon and steelhead life cycle modeling completed for the CRSO draft EIS, and an alternative breaching lower Snake River dams and spilling to 125 percent TDG at the four lower Columbia River dams.
The ongoing study was initiated in 1996 by states, tribes and the U.S. Fish and Wildlife Service to estimate salmon survival rates at various life stages, CSS Coordinator Jerry McCann said in introducing the half-day webinar. The CSS analyses began with Snake River species, and were designed to assess the effects of the hydro system on state, tribal and federal hatcheries, and to determine whether transporting juvenile fish can compensate for the effect of the dams, he said. The CSS Oversight Committee began developing life cycle models in 2013.
As part of last year's CSS—at the request of the U.S. Army Corps of Engineers, the Bonneville Power Administration and the Bureau of Reclamation—scientists analyzed the six operational alternatives for the draft EIS, which include various levels of spill, including one alternative that would breach the lower Snake River dams. Those results were included in the draft EIS when it was released on Feb. 28.
A seventh alternative—added to provide a SAR-focused scenario—combined breaching the four lower Snake River dams in Multiple Objective 3 with increasing spill at the four lower Columbia River dams to 125 percent TDG in Multiple Objective 4, and was called Multiple Objective 34, or MO 34.
The analysis of all seven alternatives was released as Chapter 2 of the 2019 CSS, which was published by the Fish Passage Center Feb. 28.
Bob Lessard, quantitative fisheries scientist with the Columbia Inter-Tribal Fish Commission, said during the webinar that the analyses reapplied life cycle modeling done in the 2017 CSS. But instead of analyzing various spill levels under high-, medium- and low-flow water years, they used the 80-year water record in the CRSO draft EIS. The 2017 life cycle model looked at Grande Ronde fish under multiple spill scenarios, and breaching of the four lower Snake River dams.
Steve Haeseker, a fishery biologist for USFWS, said four spill levels were evaluated using five metrics—juvenile survival, juvenile fish travel time, ocean survival, smolt-to-adult returns and the transport to in-river ratio, which measures the relative benefits of transporting juvenile fish compared to leaving them in the river for downstream migration.
The "non-federal MO34 alternative demonstrated the greatest expected improvements across all biological response metrics, compared to all of the federal CRSO-EIS alternatives," the analysis stated. "On average, the non-federal MO34 alternative exceeded the 4 percent average SAR regional goal. The lower end of the predicted SAR range for MO34 was above 1 percent for both Chinook and steelhead, indicating that further population decline would be avoided."
In an earlier presentation, Tim Copeland, coordinator of Idaho Department of Fish and Game's wild salmon and steelhead monitoring program, explained the history of using SARs to measure salmon and steelhead recovery. He noted that the Northwest Power and Conservation Council set a recovery goal of getting between 2 and 6 percent of Columbia River smolts produced in the basin to return as adults.
That goal is based on a modeling exercise from the late 1990s, which looked at data for Snake River spring and summer Chinook, he said. The study found that for a 100-year survival standard, more than 2 percent of smolts had to return to spawn; greater than 4 percent must return for a 48-year recovery standard; and greater than 6 percent must come back for a 24-year survival standard.
The goal was extended to other species, although some—like Snake River steelhead—are more difficult to determine due to a more complex life history.
In general, scientists have found that when steelhead fall below 1 percent smolt-to-adult returns, that's less than needed to replace the current population. And when they are greater than 2 percent SARs, they are above replacement, and rebuilding their population, Copeland said.
He noted SARs are a good performance metric, and that smolt-to-adult returns of at least 4 percent are needed for a healthy and harvestable population. "We're not going to get there if the only mark is 2 percent," he said.
Haeseker focused on SARs in his presentation on the CSS cohort-specific models that analyzed the CRSO draft EIS alternatives, plus the MO 34 alternative.
He noted that only the MO 34 alternative and MO 3—the draft EIS alternative that would breach the lower Snake River dams and increase spill to 120 percent TDG—would achieve SARs higher than 4 percent. According to the analysis, under MO 34, predicted SARs of yearling Chinook from Lower Granite Dam returning to Bonneville Dam would average 5.1 percent, and steelhead would average 6 percent. Under the dam breaching alternative, an average of 4.2 percent yearling Chinook and 5 percent of steelhead would make the same journey. And under the preferred alternative, 2.7 percent of yearling Chinook and 2.3 percent of steelhead would return as adults.
Looking across 80 water years, the probability of SARs less than 1 percent under the preferred alternative is 36 percent for yearling Chinook, and 39 percent for steelhead, he said. Under the CSS's alternative, the probability drops to 15 percent for yearling Chinook and 8 percent for steelhead, he said.
The MO 34 alternative was also the best option for fish in the other metrics measured, Haeseker said.
Predicted juvenile survival from Lower Granite Dam to Bonneville Dam was highest, averaging 70.2 percent for yearling Chinook and 86.6 percent for steelhead. That compares to juvenile survival rates of 60.5 percent for yearling Chinook and 64.5 percent for steelhead under the preferred alternative.
The average time for juveniles to travel from Lower Granite Dam to Bonneville Dam under the CSS alternative is 11.8 days for yearling Chinook and 10.4 days for steelhead, compared to 14.7 days for yearling Chinook and 15.8 days for steelhead under the preferred alternative. Ocean survival rates—or the percentage of fish that make it past Bonneville Dam as juveniles and return to Bonneville Dam as adults—are also higher under the MO 34 alternative, with 6.7 percent of yearling Chinook and 4.9 percent of steelhead surviving. Under the preferred alternative, 5.5 percent of yearling Chinook and 3.9 percent of steelhead are predicted to survive the ocean stage of their life cycle.