The Robo-Fish that Will Save Millions of Salmon

Salmon Smolt. Image credit: Alaska-in-Pictures.com

One little-known problem with the giant hydroelectric dams of the Columbia River in the Pacific Northwest is that they kill salmon, millions each year. It’s not just the adult ones going upstream to spawn, which have gotten lots of attention; it’s the young ones heading downstream. As many as 10 percent of salmon smolt perish as they try to wriggle through the whirling blades of hydroelectric turbines.

A solution is on the way, and I wrote about it in a story for Popular Mechanics that was published online yesterday. The dams of the Pacific Northwest will probably be fitted in the next decade with a new generation of fish-friendly turbines. That they are so friendly is due to a nifty gadget you’ve never heard of: the Sensor Fish.

I’ll save my breath and let you read the fascinating story here.

But I do want to add one salmon nugget that didn’t fit in the story. The Sensor Fish is not just facilitating the redesign of turbines, but shining a light into another aspect of salmon behavior — and in the process is saving even more fish.

The Sensor Fish. Image Credit: Pacific Northwest National Laboratory

The Sensor Fish’s key contribution has been to flip the science of fish mortality on its head. Observers thought that what was killing salmon in hydroelectric dams was the blunt trauma of striking the turbine blades, or maybe concrete. But the Sensor Fish and its armory of sensors discovered that the culprit was an abrupt change in pressure as a smolt falls past the blades.

The pressure drop sometimes causes a fish to “burp” from its internal air bladder so by the time it reaches the tailrace (the bottom pool of the dam) it is negatively buoyant. In other words, it sinks like a stone. In order to restore its internal equilibrium, the smolt immediately surfaces to gulp some air. And at the surface an enemy awaits.

Birds of prey have figured out that the tailrace of a dam is all all-you-can-eat salmon buffet. They swoop down on the traumatized, beleaguered fish and add to salmon mortality.

Dr. Tom Carlson, the guy who invented the Sensor Fish, told me that awareness of this phenomenon has led to an easy fix. Managers of dams in the Pacific Northwest are starting to place nets over the tailraces of dams to frustrate the birds and give salmon smolts a little breathing room.

Keep an eye out for the Sensor Fish story in the “Tech Watch” section of Popular Mechanics in the May print issue. It will be accompanied by a sweet graphic that reveals how the Sensor Fish does its magic.