The proposal by U.S. Fish and Wildlife Service, tribal, state and other biologists to test higher spill at the eight dams on the Columbia and Snake rivers is a continuation of a long scientific debate by scientists with competing views.
Here is a quick look at the science debate.
So what are the biologists proposing?
They want to see if increasing spill at the dams to a level that would increase the amount of dissolved nitrogen gas above current limits will increase survival of the migrating juveniles. They acknowledge there is some risk that more fish will die because the high nitrogen levels may give them the “bends,” like divers get.
But they believe the fish will quickly leave the pools below the dams before they are harmed. But since more salmon will be diverted from the hydro turbines, these scientists believe a higher percentage of salmon will leave the Columbia for the Pacific healthy.
If, as their models show, as many as four percent of the salmon and steelhead that spawn in Idaho and eastern Oregon and Washington return to spawn as adults, that could lead to the recovery of the wild stocks.
Since spilling the water over the dams also helps upper Columbia salmon and steelhead, it has more impact that breaching the four Snake dams.
So why isn’t the National Oceanic and Atmospheric Administration’s Fisheries Service embracing this option?
First the federal agencies that operate and pay for the dam and salmon programs argue the biological opinion, which is the draft document released last week, doesn’t need to get the salmon to recovery under the federal Endangered Species Act. They say by law the goal is simply to offset the effects of the dams.
Secondly, their biologists have always disagreed with the tribal, state and U.S. Fish and Wildlife Service about the basic science. Back in the 1990s when the Comparative Survival Study group began its work 1998 it argued that the migration through the dams, both by spill and by barges caused a delayed mortality in salmon after they entered the Columbia estuary below Bonneville Dam near Portland, Ore.
The NOAA scientists along with those for the U.S. Army Corps of Engineers and the Bonneville Power Administration and the University of Washington disputed their assertion. But over the last 15 years the evidence of delayed mortality became nearly indisputable.
And that evidence showed the delayed mortality is even higher for salmon that are collected in screens over the hydro turbines and barged downriver. This undercut the major mitigation program at the dams, the barge and collection system that allowed more water to run through the turbines and produce revenue.
The dam managers came up with a new technology, fish slides, that improved survival at lower flows of spill, which they now support. And their biologists argued that steelhead still do better in the barges so they called for less spill and more barging in the late spring.
They also believe there is too much risk in allowing nitrogen levels to rise above current limits.
But U.S. District Judge James Redden called for maximum spill, putting his weight behind the Comparative Survival Study scientists. Up until this year they argued that breaching the four dams was the best way to speed flows and juvenile salmon down the rivers and improve survival.
That doesn’t seem important now that record runs of fall chinook are swimming back to spawning grounds on the Columbia and Snake. But the run of fall chinook, which could reach 1 million adults, is due in part to cooler temperatures from upswelling currents in the Pacific Ocean that increase the amount of zooplankton which young salmon eat and reduces the numbers of predators.
These conditions have largely been around since the late 1990s. In 1995, when ocean conditions favored predators and not zooplankton, fewer than 1 million salmon total returned including spring, summer, fall chinook and sockeye.
There also was very little water spilled over the dams intentionally in those days. As many salmon as possible were loaded on to the barges.
But the scientific debate, fueled by federal agencies that can produce more money when they run more water through the hydro turbines, will continue.