On the outside, chum and coho salmon don’t seem all that different from one another, not when you consider the variety of fish in Puget Sound — from herring to halibut along with dozens of other odd-looking creatures (EoPS).
But we know that if you place coho in stormwater taken from a heavily traveled roadway, the coho are likely to die within hours. But if you do the same thing with chum, these hardy fish will barely notice the difference.
Researchers began to observe the varying effects of pollution on different species of salmon years ago. In 2006, I reported on studies by researcher Nat Scholz of the National Marine Fisheries Service, who discovered that coho would swim into Seattle’s heavily polluted creeks to spawn, but they wouldn’t get very far. Within hours, they would become disoriented, then keel over and die. (Kitsap Sun, June 10, 2006)
Later, Jenifer McIntyre, a researcher with Washington State University, collaborated with Scholz to refine the studies, exposing adult coho and later young coho to stormwater under controlled conditions. Much of that work was done at the Suquamish Tribe’s Grover’s Creek Hatchery in North Kitsap. The researchers also measured the physiological effects of pollution on zebrafish embryos during their early stages of development.
Working at the Washington Stormwater Center in Puyallup, Jen made a remarkable discovery that has dramatically changed people’s thinking about stormwater treatment. She found that if you run the most heavily polluted stormwater through a soil medium containing compost, the water will no longer have a noticeable effect on the sensitive coho. Rain gardens really do work.
Jen’s findings and related stormwater issues were described in a story I wrote two years ago for the Kitsap Sun, “Stormwater solutions key in fight for Puget Sound.” The story is part of a two-year project we called “Taking the Pulse of Puget Sound.”
Now, Jen, who recently joined the faculty of WSU, is beginning a new phase of her research, probing deeper into the physiological responses of coho salmon when exposed to polluted stormwater. She told me that the varying responses of coho and chum offer clues about where to look for problems.
“It is very interesting,” she said. “As biologists, we understand that there is variability among species. But we would expect, at least among salmon, that things would be pretty much the same.”
Researchers in Japan have discovered that different kinds of fish have different subunits in their hemoglobin, which are the proteins in red blood cells that carry oxygen to the vital organs. Since coho and other salmon may have different forms of hemoglobin, oxygen transport in the blood is a good place to start this investigation, she said.
From there, the issues of blood chemistry get a little technical, but the ability of red blood cells to carry oxygen can depend not only on the form of hemoglobin but also on the pH (acidity) of the blood, she said, and that can be altered by drugs and other chemicals.
Another thing that researchers may be seeing is “disseminated intravascular coagulation,” a condition that results from clotting in the lining of the capillaries. DIC can reduce or block blood flow where it is most needed and eventually cause organ damage. That’s an area for more research, Jen said, noting that these investigations are moving forward in collaboration with researchers at NMFS and the U.S. Fish and Wildlife Service.
Meanwhile, Jen is working with chemists at the University of Washington’s Center for Urban Waters in Tacoma to figure out which substances — out of hundreds of chemicals found in stormwater — could be causing these deadly effects on fish.
If isolating the dangerous compounds proves too difficult, researchers might be able to start with the original toxic sources, perhaps exposing fish to chemicals found in tires, oil, antifreeze and so on, Jen said. For those effects, it might be good to begin the investigation with the well-studied zebrafish embryos, which are transparent and can be observed closely throughout their embryonic development.
Needless to say, this is a field of intense interest. If researchers can discover what is killing coho, they might begin to understand why the recovery of chinook salmon in Puget Sound has been so slow. Chinook, which could be added to Jen’s studies, are listed as a threatened species under the Endangered Species Act and are the preferred prey of Puget Sound’s killer whales, which are listed as endangered.
Two recent articles discussed the relative hardiness of the chum compared to coho salmon:
- Chum salmon more resistant to runoff pollution,” Kitsap Sun, Tristan Baurick.
- “Saving salmon in the wild – is chum the king?” WSU News, Linda Weiford.