A celebratory season for many anglers enjoying strong returns of sockeye and pink salmon masks a perilous situation unfolding beneath the surface for another iconic species. A recent study from Simon Fraser University delivers a stark warning that coho salmon populations along the north and central coasts of British Columbia are facing a severe threat of collapse, revealing a troubling disconnect between recreational fishing success and the underlying health of the ecosystem.
The new research, published in the Canadian Journal of Fisheries and Aquatic Sciences, highlights a dramatic downturn in coho numbers, driven by a combination of climate change and fisheries pressure. Researchers found that the number of spawning coho has plummeted, and their ability to reproduce successfully has been crippled by marine heatwaves. The findings underscore long-standing concerns voiced by First Nations and suggest that without immediate intervention, a cornerstone of coastal ecosystems could be lost.
Extent of the Population Drop
The study provides a detailed and troubling picture of the decline. Investigators analyzed coho populations in 52 distinct river systems situated along the central and northern coastline of British Columbia. The data revealed that the number of spawners—adult salmon that successfully return to their freshwater birthplaces to reproduce—fell by an alarming 37 percent in 2020 when compared against the average numbers recorded between 2000 and 2015. This significant reduction in returning adults is a direct indicator of dwindling population sizes and a failing capacity to sustain their numbers.
Beyond the sheer drop in spawners, the research uncovered a collapse in what scientists call productivity. This metric measures the number of surviving offspring produced per spawner and is a critical gauge of a population’s resilience. The study found that this productivity collapsed for many coho populations, particularly during the intense marine heatwaves that occurred near the end of the last decade. This failure to produce a robust next generation signals that the salmon are struggling not just to survive their time in the ocean but also to successfully reproduce even if they do make it back to the rivers, compounding the overall population decline.
Intensifying Climate Pressures
At the heart of the coho’s struggle are unprecedented changes in their ocean environment, primarily driven by marine heatwaves. These events are characterized by prolonged periods of abnormally high ocean temperatures, which fundamentally alter the marine food web and place immense stress on cold-water species like salmon. The warmer water directly impacts coho in two critical ways: it increases their metabolic rate while simultaneously reducing the availability of their food sources.
“Salmon are typically considered cold water species,” explained Kyle Wilson, the study’s lead author and an assistant professor at Simon Fraser University. He noted that as ocean temperatures rise, coho salmon experience heat stress, which forces them to burn more energy and require more food just to survive. However, the very same heatwaves negatively affect the smaller fish and marine organisms that coho prey upon, leading to a scarcity of food when the salmon need it most. This creates a desperate scenario where metabolically stressed fish are unable to find enough sustenance, potentially leading to starvation and significantly reducing their chances of surviving the arduous journey back to their spawning grounds.
Fisheries and Food Competition
While climate change delivers a powerful blow, it is not the only factor imperiling the coho. The study also points to the combined pressures of overfishing and unexpected competition from other salmon species. Researchers assessed how commercial and recreational fishing activities across multiple jurisdictions, including Canadian, U.S., and Indigenous fisheries, hinder the recovery of vulnerable coho populations. Even with some conservation measures in place, the cumulative impact of these harvests adds significant pressure on a species already weakened by environmental stressors.
Furthermore, coho are facing increased competition for limited food resources from pink salmon. Pink salmon numbers in the North Pacific Ocean have surged to all-time highs, partly due to the large-scale output of industrial hatcheries. This explosion in the pink salmon population means more mouths competing for the same prey, putting coho at a distinct disadvantage. The study also notes that coho are a less visible species to the general public compared to sockeye and pink salmon. Their migration occurs later in the year, stretching into the winter, which makes them harder to monitor and allows their decline to proceed without the widespread public alarm that might accompany the collapse of a more visible summer-run species.
Collaborative Science and Indigenous Knowledge
This critical research was not conducted in isolation; it represents a collaborative effort between several key groups. The study brought together scientists from Simon Fraser University and the Wild Salmon Center, officials from Fisheries and Oceans Canada, and, crucially, the Central Coast First Nations. This partnership underscores a growing recognition that effective conservation requires the integration of rigorous scientific data with the deep, place-based knowledge of Indigenous communities who have managed these resources for millennia.
The scientific findings strongly support the warnings that First Nations have been issuing for years about the deteriorating health of coho stocks. “Alarm bells should be ringing,” stated Wilson, emphasizing the gravity of the situation. “Our findings support what First Nations have been saying for years – coho salmon populations are under serious threat.” This alignment of traditional ecological knowledge and modern scientific analysis provides a powerful, unified voice calling for urgent action to address the crisis.
Prospects for a Rebound
Despite the dire warnings, the researchers suggest that hope is not lost. The study offers a silver lining by highlighting the natural resilience of coho salmon. History has shown that these populations can and have recovered from perilous lows in the past when conditions improve and effective management strategies are implemented. The key is responsive and adaptive management that can react quickly to changing ocean conditions and relieve pressure on the fish when they are most vulnerable.
“The good news is that coho are resilient,” the study notes. “They have been in this position before and their numbers have recovered rapidly when the right levers have been pulled and environmental conditions are favourable.” This conclusion places the responsibility squarely on resource managers and policymakers. Urgent and decisive action to mitigate the impacts of overfishing, protect critical habitats, and address the overarching threat of climate change will be necessary to pull these vital salmon populations back from the brink and ensure their survival for future generations.