Why are salmon dying when they reach saltwater?August 22nd, 2013 by cdunagan
A new research program, announced yesterday, will work to untangle the mystery of what is killing young salmon after they leave their natal streams. The program is being coordinated in both Washington state and British Columbia — by Long Live the Kings on the U.S. side and by Pacific Salmon Foundation in Canada. See today’s Kitsap Sun (subscription required).
I have conducted hundreds of interviews about salmon through the years. Biologists can usually explain what makes a good salmon stream: clean water, sufficient gravel, vegetation to provide food, woody debris to provide protection and so on.
What they cannot explain very well is what young salmon need to survive in saltwater. Is it clean water, as in freshwater environments? Is it a particular kind of plankton for food, or maybe natural shorelines to provide protection during migration? Is the increased marine mortality of salmon the result of disease or predators? All may be factors, but which ones really count?
When asked to explain why salmon runs are coming in larger or smaller than predicted, salmon managers typically fall back to two words: “ocean conditions.” Conditions may be good or bad in a given year, but what makes good or bad conditions cannot be answered very well.
Biologists who predict salmon runs talk about the “black box” that salmon swim into when they leave the streams and swim back out of when they return. It’s a way of saying that the computer models used to predict salmon runs have a blind spot when it comes to the deep, dark ocean — which we now believe includes the estuary at the edge of the stream, where the salmon change from being a freshwater fish to being a saltwater fish.
“What is currently recognized as a black box appears to be a black hole for salmon recovery,” Jacques White, executive director of Long Live the Kings, told me yesterday in an interview. “If we don’t know what is going on, we can’t make decisions for salmon recovery. It makes it difficult to manage the stocks coming back.”
That’s where the cross-border research program comes in, and it’s no wonder that salmon biologists are excited about the prospect of breaking into the black box. It won’t be easy to track the tiny fish after they leave the streams or to figure out where things are going wrong, but new technology will help. The project is proposed for $10 million in the U.S., with an equal amount in Canada.
Review the Long Live the Kings website for other information about the Salish Sea Marine Survival Project. To go deeper into the ideas behind the project, download the proceedings, notes and other information from November’s Salish Sea Workshop Series.
Meanwhile, efforts to improve estuarine and shoreline conditions will continue, using natural conditions as a guide. On Monday, I covered the final step in the Union River estuary restoration, which involved breaching an old farm dike in two places. I watched as the waters of Hood Canal, held back for a century, began to reclaim 32 acres of saltwater march. Check out the story and video in the Kitsap Sun (subscription required).