Protecting salmon in coastal Canada could have benefits that extend beyond the water they swim in and can have profound impacts on the surrounding landscape.
Skeins of wispy clouds obscure the tops of distant forested mountains, reflected in calm waters. On this midsummer morning at least, the Pacific is living up to its name on this stretch of Canada’s west coast. Backpacks and thermoses in hand, four researchers tread down a wooden strutted ramp to board a boat named the Keta. Scientist Allison Dennert starts the boat, steering away from the dock into the broad channel, glancing at the map on the video console. A brief stop at the Bella Bella dock, to pick up research technician Sarah Humchitt, completes our crew of five.
Research assistant Lisa Siemens points at a bald eagle on the shore. “It’s bad luck to point at eagles,” says Humchitt, a member of the Heiltsuk people, one of Canada’s First Nations. Humchitt grew up in the tiny, mainly indigenous town of Bella Bella before spending her high school years in Vancouver. Back for the summer she’s part of Dennert’s all-female scientific team.
Siemens is curious about her faux pas of eagle pointing. “What about other birds, or is it only eagles?” she asks. “Only eagles,” says Humchitt, and conversation turns to a timid fawn spotted on the shore, and whether we might see humpback whales or orcas on our way.
Like the eagle, Dennert and her team are also hunting fish. All five species of eastern Pacific salmon – chum, coho, chinook, pink, and sockeye – spawn in this region of Canada. Salmon are a vital food supporting ecosystems and First Nations’ cultures and economies here for at least 7,000 years.
Pacific salmon are travellers. Hatched in freshwater rivers where they grow into smolts, they then make dangerous journeys to the sea. Those that arrive safely feast on sea riches for several years, each species with a slightly different lifestyle. Once mature, they return to their natal rivers in late summer and autumn, fighting their way up streams to spawning grounds. In rivers, nutrients typically flow downstream but salmon on a breeding mission are counterflow, carrying important nutrients in reverse to the upper reaches of river systems.
There are still many questions about how homeward bound salmon enrich the nutrient-impoverished habitat along stream banks. To answer some of them, this team is travelling up a stream that salmon seldom swim.
Some 35 minutes from the Bella Bella dock, four of the team – clad in chest waders – take turns dangling from the bow of the metal boat, jumping down into the knee-deep waters along the rocky barnacled shore. When they have all disembarked, Dennert backs the boat away, anchoring it before hopping onto an orange plastic kayak and paddling in to the beach.
Bushwhacking along a rough trail, scrambling over and under mossy logs, Dennert along with field assistants Siemens, Humchitt and Emily Yungwirth carry backpacks and two collapsible squares of bungy cord strung through plastic pipe. Emerging from rainforest trail to a shallow rocky stream, they navigate slippery rocks, cans of bear spray belted to hips. The slow slosh of waders is meditative as the stream banks widen into a lush grassy meadow.
This is where Dennert is testing how fish feed flowers. Here on this verdant bank are the experimental plots, each containing a grid of four one metre-square patches of grass. Last autumn when spawning salmon arrived in the area, though not on this smaller stream, each set of four squares got a different treatment. The first received a stinky dead salmon, pegged under plastic netting to foil furry scavengers. Square two got seaweed. Square three, seaweed plus salmon. The fourth square is unaltered grass.
Now, with the meadow turning green again after the winter snows, Dennert is back with her team. All that remains of the salmon are the bones. Dennert and Yungwirth take the odd numbered plots, Siemens and Humchitt take the evens. It’s a friendly race to tally plants inside the squares. The four most common meadow wildflowers – yarrow, common red paintbrush, silverweed, and Douglas aster – get extra close attention. “Two paintbrush…” says Dennert. “One meadow barley,” says Yungwirth, crouching to pore over plants at eye level. Meticulous flower counting finishes in this plot.
Will plants fertilised by salmon produce more or bigger flowers? Will their nutrients affect what grows and which pollinators visit? And can coastal forests rely on a stored nutrient bank during lean years when few salmon return? This is what the team hope to answer.
The natural laboratory
We’ve known for over 20 years that nutrients like nitrogen and phosphorus from salmon make their way into coastal forests. “That’s not particularly surprising given that nearly 500 million fish return to the Pacific coast every year,” says Dennert,
Several billion kilograms of decaying flesh is bound to find its way from the rivers, onto the land and into the cells of the creatures living there. Perhaps most iconically, it passes through the bellies and out as the poop of predators like grizzly and black bears. Natural tracers show a salmon signature in all manner of organisms from bugs and bears to trees. But what does this nutrient bonus mean?
Dennert’s experiment – looking at how meadow plants grow with and without a nutrient bonus – will provide clues about how ecosystems would look without salmon, “which is becoming a very real possibility,” she says. “Last fall, I walked a stream that had 5,000 pink salmon return to it in 2017. In 2018, we counted only 26.”
Salmon populations are facing pressure from multiple stressors including climate change, pollution, fisheries, habitat degradation and habitat loss across the Pacific coast. While many salmon populations on the Central Coast of British Columbia are healthy, others are depressed, declining, or of conservation concern. The status of about 70% of the salmon populations here is unknown. But many streams here are healthy, making it an excellent natural laboratory.
Dennert’s work builds on a slowly accumulating understanding of how salmon feed the land. Salmon biologist Tom Quinn at the University of Washington, Seattle, and colleagues including his then graduate student Rachel Hovel, now at the University of Maine, Farmington, conducted an elegant if somewhat accidental experiment published in 2018. During sockeye surveys on Hansen Creek, southwestern Alaska, “we would walk up the stream and count the salmon,” says Hovel, noting cause of death, then throwing carcasses to one bank. Twenty years of this lop-sided tossing created an opportunity to test nutrient enrichment. Comparing growth and nitrogen content in spruce trees on the stream’s north and south sides, they found a signal indicating that salmon indeed fed and sped up tree growth.
Dennert’s doctoral supervisor John Reynolds, an aquatic ecologist at Simon Fraser University, also previously examined how plants respond to salmon streams. Reynolds partnered with the Heiltsuk Nation to survey salmon and plants on fifty watersheds on the Central Coast. Hugging over 6,000 trees to measure their diameters, they found a strong correlation between streams with more salmon and nutrient-loving plants and trees.
Other work has shown that flowers can coordinate their blooms with the arrival of salmon, helpful for their pollinators that might eat their decaying remains, too.
Because much of the previous work was correlational, the Reynolds lab began experimenting. Starting on a Central Coast stream that salmon couldn’t access because of a waterfall, Reynolds and Hocking set up experimental sites. It involved hauling heavy dead chum salmon “in dripping green garbage bags” through prime grizzly habitat so they could see what would happen to the vegetation at the site if the fish were left there. On 11 streams, their experiment showed that plants draw nitrogen from salmon in spring, many months after carcasses are deposited.
Dennert is still collecting data, plant by plant, bug by bug, flower by flower, and much of her analysis is yet to come. Preliminary results suggest that some plants fed by salmon, like yarrow and aster, have bigger flowers, with bigger leaves. Those bigger flowers may attract more pollinators, helping diversity to flourish. And there are hints that if salmon disappear from some of these streams – perhaps never to return – the diverse communities that depend on them will be poorer.
Beyond the water
Bella Bella’s Heiltsuk community is keenly interested in Dennert’s focus on the impacts of salmon beyond the water. Local salmon fishing guide Howard Humchitt says the learning goes both ways.
We really need to understand the biological consequences of what the salmon are doing for these ecosystems if we want to manage them effectively - Allison Dennert.
The Canadian government’s Wild Salmon Policy states that salmon management must consider the ecosystems that salmon return to, explains Dennert. So “we really need to understand the biological consequences of what the salmon are doing for these ecosystems if we want to manage them effectively,” she says.
Ecosystem-based management currently gets little attention by government fisheries, suggests Reynolds. But that may matter less now that indigenous communities like the Heiltsuk are gaining back the autonomy to manage their own lands and resources.
Before European contact, explains Howard Humchitt, different Heiltsuk families would manage different rivers and ocean areas. “Before the government took over, if a river had a bad year [for salmon] because of a flood or blockage… we would say ‘No, that one’s done for a while,’ and go back when it was replenished,” he says. “Sometimes that took half a lifetime.”
Those old practices, says Humchitt, are not lost, but they’re forgotten.
Now late August, Humchitt motors his boat slowly home after a day of fishing. This time of year, pink and chum are usually jumping, but he’s seen few today. “I’m hoping that with a mild dry summer that everything is still offshore,” he says.
But rains are coming. More than 100 mm (four inches) of rain is expected overnight. And rain, says Humchitt, “will give the fish a push to come home.”