New Paper Looks At Sultan River, Pugetropolis Pink And Chinook Salmon Abundance

There’s always a bit more giddiness around the North of Falcon salmon forecast reveal in odd years, when pink salmon return, but some new information about the species’ local impact has me smacking my forehead – and hoping for bonus limits.

Later this week we’ll find out how many millions of my darling little humpies are expected to return to Puget Sound streams. They’re a native salmon species that has exploded like my pink Buzz Bomb collection has over the past 25 years. A record 10.3 million returned in 2009.

But that boom, probably fueled by the heating of the North Pacific and climate change that appears to have made the ocean more productive for Oncorhynchus gorbuscha, may also be negatively affecting the productivity of Puget Sound’s Chinook here at home – and in multiple ways.

A new paper that in part looked at the abundance of both salmon species in the Sultan River not only found 36 percent fewer Chinook in the Snohomish County stream in odd years compared to even ones, but sharply lower reproductive success too.

That’s because most Chinook end up spawning higher up in the Sultan in odd years. They largely abandon the relatively gravel-rich lower river in humpy years and move into the steeper, tighter and much less productive canyon stretch of the Sultan.

Their fry-per-redd productivity drops from 1,819 plus or minus 230 in even years, when 43 percent spawn in the lower 3 miles, to 395 plus or minus 149 in odd years, when 79 percent spawn in the canyon.

In those odd years, those lower 3 miles of the Sultan – essentially from the mouth at the town of Sultan to just above the powerline crossing near the end of Trout Farm Road – are swamped with 80 percent of the run of pinks, which can be 300 times as numerous as Chinook.

The data comes from Snohomish County Public Utility District spawning surveys conducted in all falls from 1991 through 2022 except for 2011 (a turbid year), and a screw trap operated in the first half of the year from 2012 through 2023 except for two years.

Why or how humpies are bullying larger Chinook off the Sultan’s best spawning grounds is hard to say, as no research has been done on interactions on the gravel between the species in North America, the authors of the paper state. But they note that in European rivers invaded by pinks in recent years, the diminutive fish “reportedly attack and alter the migration and distribution of spawning Atlantic salmon.”

The study, which was published earlier this month in the Canadian Journal of Fisheries and Aquatic Sciences, also found a similar 36 percent dropoff in Chinook spawner abundances in odd years in King County’s Green River once pink salmon colonized it around the turn of the millennium.

Before then, there was no such biennial pattern, nor is there to this day on Lake Washington, where until recent years there were no pink salmon (a few were seen in 2021 and 2023), the paper states.

Previous research also found an every-other-year overlap effect in young Skagit River Chinook scale growth rates, which were “significantly less” in even years, when their outmigration coincides with pink salmon smolts leaving their natal rivers.

The authors of this new paper, who include Greg Ruggerone of Natural Resources Consultants who has done multiple papers on pinks over the years, and three PUD biologists and environmental coordinators, found similar biennial spawner abundance patterns in seven Puget Sound Chinook systems starting in 1997.

Around that time, southern resident killer whales also began to show signs of decline and exhibit their own annual up and down mortality and birth patterns.

“Biennial patterns in pink salmon, Chinook salmon, and SRKW support the hypothesis that pink salmon adversely affected abundance of Puget Sound Chinook salmon and influenced the decline of SRKW since 1997,” the authors write.

The resident orcas have a very strong preference for eating Chinook and only “rarely” chew on pinks. Researchers have hypothesized that the abundance of pinks messes with the SRKWs’ echolocation, making it harder to hunt kings in the mixed-stock schools of salmon that come through the Whulge. State and federal hatchery managers have increased production of clipped Chinook by millions of fish annually to boost forage availability for orcas, though it’s been fought tooth and nail by wild fish groups.

Ruggerone et al note that pinniped predation by harbor seals and sea lions, which have been implicated in the decline of Chinook, probably would not account for the up-and-down spawner abundance of Chinook they see.

Their paper was first reported on this week by both the Columbia Basin Bulletin and Clearing Up.

The authors say their work and that of others “highlights the need for an ecosystem approach to manage the large and increasing abundances of pink salmon in the Salish Sea,” and they suggest that “Live harvest techniques, such as fish traps, fish wheels, weirs, and reef nets, could be deployed to harvest pink salmon in excess of what is needed to sustain the population while simultaneously live-releasing non-target salmonids.”

Fish wheels and fish traps are illegal in Washington, but the Lummi Nation uses reef nets in North Puget Sound.

I’m just gonna butt in here for a second, but as we begin the salmon-season-setting process, if there’s EVER been an argument for bonus limits on pinks, this is it – what do you say, Kelly S and Kelly C? Help us help save the kings and the orcas!

And as a licensed and practicing keyboard fisheries biologist and salmon harvest manager myself, I also wonder whether restricting Snohomish and Skykomish fisheries during the heart of the pink run might actually hurt Chinook more than allowing anglers to fish over the ESA-listed stock while trying to catch and remove humpies. Very low expected numbers of wild summer/fall Chinook have been crushing angler opportunities in the system in recent years, and now we know a direct cause.

Ahem, back in more sober salmon circles, Ruggerone et al also call for the “curtailing” of the massive production of hatchery pink salmon by Alaska and other entities that Northwest salmon stocks have to compete with while foraging in the North Pacific.

But in the meanwhile, their new paper illustrates that high pink salmon abundance issues may not just be limited to the northern ocean.