PUYALLUP, Wash. – Chum rule. In the same toxic stormwater brew that killed coho salmon in less than three hours, their chum cousins did just fine.
It’s a king-sized mystery that Washington State University researcher Jenifer McIntyre is trying to solve. The answer, she said, will tell an important story.
“We’ve known that chum seem less sensitive in urban streams than other salmon species but the fact that polluted road runoff caused no visible symptoms of toxicity – that surprised us,” said McIntyre, an aquatic ecotoxicologist at the stormwater program at WSU’s Puyallup Research and Extension Center.
Wild salmon are a symbol of survival in the Pacific Northwest. The fish fuel the region’s economy, define the culture and fortify culinary needs and traditions. With this in mind, McIntyre is working with researchers of the National Oceanic and Atmospheric Administration and the U.S. Department of Fish and Wildlife to figure out practical ways to prevent human-tainted streams from snatching the future from these iconic fish.
In 2015, McIntyre co-authored a study that for the first time documented the fatal effects of urban runoff on coho salmon, commonly known as silvers. By monitoring urban creeks in Seattle for nearly a decade, she and her colleagues observed that adult coho died at high rates during rainfall or after a passing shower.
A toxic cocktail of oil, metals and grime running off roads contributes to the steep die-off of coho returning to waterways to spawn, the study concluded.
But there’s a surprise catch in McIntyre’s recent round of research: When submerged in holding tanks containing the same dirty runoff, chum salmon not only survive, they appear untouched, according to preliminary findings.
“The coho? Leading up to their deaths, they grew lethargic and seemed confused, swimming erratically near the water’s surface and turning onto their sides,” she explained. “The chums? They remained healthy-looking and alert. Even their blood chemistry was relatively unaffected.”
Why chum are resilient to urban runoff as hospitable as a junkyard can perhaps be explained by their legendary drive to thrive.
“Fishermen and even fish biologists will tell you that they’re very robust, they’re like zombie monster fish,” McIntyre said.
Nicknamed “dog salmon” after the canine-like teeth it displays at spawning time, chum is the most abundant salmon species in Washington, according to the state’s department of fish and wildlife. With a few exceptions, the chum has maintained relatively high population numbers as other Pacific salmon species have shown sizable declines.
Also, while other species of salmon fry hang around in freshwater streams to eat and grow bigger before heading to sea, young chum do not. At only 1½ inches long, they begin their journey to open waters as soon as they emerge from their gravel nests.
Just why runoff toxins aren’t killing these tough-guy chums warrants deeper investigation, said McIntyre.
The question she’s trying to answer: While migrating through pollutant-laden streams, are other salmon species more like coho or more like chum?
“Salmon runs in the Pacific Northwest face widespread urban growth – especially in the Puget Sound region,” she said. “If other Pacific salmonids are more like coho, their survival rates could be severely challenged as humans continue to expand into salmon’s native range.”
McIntyre had hoped to study the ever-popular chinook, or king salmon, last fall but the number of kings returning to Seattle area streams was so low she had to postpone the work, she said. Today she’s examining the effects of stormwater on juvenile coho, chum and chinook.
The secret to all of their survival, she said, may lie within the dogged chum.