Maybe Salmon Aren't Dammed

PLOS Biology / Steelhead salmon smolt with tags

I know, I just couldn’t resist the title.  PLOS Biology published an enlightening study yesterday on the survival rates of Chinook, steelhead, and other salmon smolts (er, juveniles) swimming through dammed and free flowing rivers

The Columbia-Snake River system is home to thirteen stocks of salmon considered to be threatened or endangered.  Its also home to several dams, including the Bonneville Dam, used for hydroelectric energy.  The study team compared smolt survival in the Columbia system to the Thompson-Fraser River system in British Columbia, which is free flowing, using PIT and POST tags implanted in smolts.  Previously environmentalists and researchers have considered dams to be a primary hurdle in long term salmon recovery and survival.  But this new study suggests otherwise. 

“Surprisingly, smolts fared just as well negotiating the heavily dammed Columbia as they did going down the free-flowing Fraser. Comparing the rivers section by section, Chinook smolts traversing the dammed system actually had higher survival rates than their cousins in the Fraser. Adjusting estimates to consider the distance and time smolts had to migrate to reach the river mouth revealed that average survival rates were much higher for both species from the Snake River than for those in the undammed Fraser. In fact, no matter how they analyzed the data, the researchers reported, “survival is not worse in the Columbia despite the presence of an extensive network of dams.””

So where does that leave salmon conservation?  Well, it indicates that salmon recovery is a multi-faceted problem, which we already knew.  The researchers suggest that future research focuses on survival out in the ocean to examine stresses upon smolts that are newly entered into the ocean system.  Its important to consider, as well, that this study followed smolts headed back towards the oceans, and that survival was still rather dismal for both study sets – dammed and free flowing.  Salmon adults are still upheld at dams as they head into the Columbia system and climb fish ladders. 

Researchers also currently study how changes to the marine ecosystem – from warming oceans to potentially enlarging predator populations impact salmon runs.