A study published in the online scientific journal PLoS Biology on October 27 with the provocative headline “Dams make no damn difference to salmon survival”[1] is now being questioned by a number of scientists, including several co-authors of the study.

According to the study, young fish running the gantlet of dams on the Snake and Columbia rivers did just as well as youngsters in an undammed river. Dams are widely regarded as one of the main reasons behind the sharp decline of salmon in North America’s western rivers and a study claiming that dams make no damn difference for salmon survival is therefore destined to receive a lot of attention from dam proponents and dam critics alike.

While a number of scientists, including several co-authors, are questioning the results and cautioning about what conclusions can really be drawn from them, lead-author David Welch stands by his report. “We’re not saying that the dams have never had an effect,” says Welch. “What we all have to ask ourselves is, if survival is up to the level of a river that doesn’t have dams, then what’s causing survival problems?”

Welch has already warned against overstating what the study proves, and continues to do so. According to Welch, the results of the study do however suggest that dams might not play such a big role in the fate of endangered Columbia River salmon today, and that the situation in the ocean – where the salmon live until it migrates upstream to spawn – is of higher importance than river conditions.

Michele DeHart, manager of the Fish Passage Center[2], strongly disagree with the conclusions drawn from the study. “There’s a huge mass of scientific literature that documents the impacts of dams. It’s just huge,” says DeHart. “It’s like saying, ‘Gosh, I just did this comparison and smoking does not cause cancer.’ Would you change your mind?”

In the study, the survival rate of young salmon and steelhead heading for the ocean (so called smolts) was measured in the rivers Columbia and Snake, which are heavily dammed, and in Fraser River, which has no dams at all. To the researchers’ surprise, the recorded survival rate was around 25 percent for all smolts, regardless of whether they travelled in dammed or undammed waters. If you take into account that smolt in the Columbia River actually have to travel a longer distance, it even looks as if smolt traversing dammed waters are doing better than their counterparts in the undammed Fraser.

Environmental groups are now claiming that comparing the different rivers with each other is like comparing apples and oranges, and co-author Carl Schreck, head of the Oregon Cooperative Fish and Wildlife Research Unit at Oregon State University, warns that the study could have failed to account for fish that die in the ocean due to the stress they have been subjected to while traversing dams in Columbia and Snake.

Ed Bowles, biologist and head of fisheries for the Oregon Department of Fish and Wildlife, says that it would be better to compare how similar fish, e.g. spring Chinook, do when they spawn in the same river – some above dams and some below.

Regular salmon

Biologists keeping track of the sockeye salmon populations in central Idaho (Sawtooth Mountains) have good news to report. More sockeye than in any other year in the last two decades have made their way pass the eight dams on the Columbia and Snake rivers and returned to idaho. 507 fish have been counted so far. That might not sound much but considering that the number has been in the single digits each of the last five years and that only 16 wild sockeye returned between 1991 and 1998 it is a large improvement. It might however be too early to start celebrating as 257 sockeye returned in 2000 followed by a number of bad years.

The improvement is believed to be due to the fact that 180,000 smolts were released in Idaho lakes in 2006. Some of the returning fish are likely artificially spawned at the Eagle Fish Hatchery in Southwestern Idaho as part of a program to help boost the sockeye populations around the Sawtooth Mountains.

The 507 returning fish might be a better number than in many years but it is still no where near the historical levels of Sockeye salmon that once wandered the 900 miles from the Pacific Ocean to Idaho lakes like Redfish, Pettit and Alturas. As many as 35,000 sockeye used to return each year. The population decline is believed to be primarily due to four dams along the lower Snake River in Eastern Washington.