The plight of salmon in the Pacific Northwest is bad and getting worse -- but you can't necessarily blame the dams.
Along the Snake River in Idaho, Wyoming, Washington and Oregon, for instance, wild salmon now inhabit less than 10 percent of their range of 40 years ago.
Because eight species of salmon and steelhead that migrate through the Columbia and Snake rivers to the ocean and back are in danger of extinction, they have been placed under the protection of the federal Endangered Species Act.
One protective strategy, demanded over the last several years by conservationists, is dismantling four dams on the lower Snake River. The dams -- Ice Harbor, Lower Monumental, Little Goose and Lower Granite -- block the instinctive migratory route for salmon from the main stem of the Columbia River to their spawning grounds further upstream in the Snake and its tributaries.
One need not be steeped in the arcana of fisheries biology to see the logic here. For countless millennia, the fish swam upstream unimpeded to breed and provide the next generation of little fishies -- alevin, fry or smolt, depending on their stage of development. Then people built dams across the river. Now, the fish can no longer swim upstream unimpeded. Many die trying to reach their breeding grounds. No more little fishies. Ergo, the ESA to the rescue.
Of course, not everyone wants to remove the dams because some do not consider salmon a high priority. For example, the dams allow Lewiston, Idaho -- some 300 miles from the Pacific Ocean -- to operate a deepwater port. Why the citizens of Lewiston want a deepwater port in their neighborhood -- what with the sailors brawling in taverns and ladies of dubious reputation leaning provocatively on lightpoles -- is puzzling, but that's another matter.
Sociology aside, although the dams provide some benefit, they must be heavily subsidized. You also have to add to their costs the $800 million the federal government has spent to engineer fish ladders and other methods along the Columbia to allow the salmon to migrate both up and downstream. Those "other methods" include loading salmon onto barges, which travel through the locks of dams that otherwise would block their way, to provide portage along some of the migration path.
To date, no one has asked the the wild and proud salmon what they think of the experience. Maybe it's the reason their meat is pink.
Before the portage system and fish ladders were installed, salmon populations had been declining by 50 percent per year. Now, they are declining by much less.
"So I wouldn't say the money was wasted," said Peter Kareiva, lead ecology conservation biology scientist for the Nature Conservancy. Nevertheless, he said, if the four controversial dams were removed, it probably would not do much to help the salmon.
"In the broader context, dams alone do not explain the trouble that the salmon are in," Kareiva said. "If you remove the four dams on the Snake, the fish still must pass many dams." He added that much of the habitat on which salmon relied previously still will be cut off by other barriers, including dams.
Salmon habitat upstream has been degraded over the years, Kareiva continued. Of the 135 populations of chinook salmon in the basin, 72 of them pass through one or no dams to spawn. Despite the relatively easy time these population have of it, they still are not reproducing fast enough to save themselves over the long term. Something else is going on in the system.
Salmon and steelhead -- known collectively as anadromous fish -- represent a remarkable evolutionary story. Born in shallow fresh water streams, they migrate to the ocean not long after birth, their physiology adapted to both fresh and salt water environments. Depending on the species, they can travel thousands of miles into the deep blue, then return one to five years later, usually to the same stream from which they originated, to spawn and die.
A much-quoted 2001 paper on Snake River salmon by Gretchen Oosterhout and Philip Mundy prepared for Trout Unlimited said, "For the seven index populations together, the overall expected year of functional extinction is projected to be 2016."
Michelle Marvier of Santa Clara (Calif.) University, who has studied salmon populations in the Snake and compared them with populations elsewhere in the river system, said she found "the more dams fish have to go through, the lower the population density."
However, she added, the reproduction rate for fish did not change much regardless of how many dams they had to migrate through. In other words, population levels among the various salmon groups -- dam-challenged or not -- have stayed about the same.
So, Marvier said, although the dams in the Columbia Basin caused initial drops in population, "the dams do not appear to be preventing the Snake River salmon from recovering." The dams clearly are harmful to migrating fish, "but not all dams are equally harmful."
These results are controversial, as you might expect. A publication from American Rivers, a conservation group, said, "Dam removal has a high likelihood of success and always outperforms dam-retention alternatives."
The problem is scientists who have studied dam removal -- albeit on a smaller scale -- are not so sure the practice "works" because the effects still are largely unknown, and few scientific studies have been completed about the impacts.
The "golden era" of dam building occurred from the 1950s through the 1970s, and those dams are aging and will have to be replaced or dismantled as their 50-year useful lifetimes end over the next two decades.
Gordon Grant, a hydrologist with the U.S. Forest Service, said there are 75,000 aging dams in the United States. Although most of the controversy has focused on the large dams, such as those on the Snake, most of these old dams are small.
"In spite of all the interest and enthusiasm," Grant said, "we actually know very little about the biophysical consequences of removing dams."
John Harbor, a geomorphologist at Purdue University, said, "Dam removal is in the realm of uncertain science." He studied the removal of a dam in Wisconsin. Although the bank levels and river flows settled in within a few years, the mussel populations in the area were decimated.
Mussels are among the most endangered of aquatic invertebrates. "Ecosystem recovery is a complex set of tradeoffs," Harbor said. "Not all are viewed as positive ... that's a human choice to make."
As Harbor added, dam breaching does not restore the river environment to the state that existed before the dam was built. Instead, he said, "We are more likely to create a new reality."
