Such is the curse of salmon’s shifting baseline: coming to accept as normal what is in fact a diminished state of affairs.

Usually baselines are set according to present circumstances. Sometimes, though, it’s the historical record against which the present moment is measured—and when that history is revised, our understanding of the present, of where the baseline ought to be, undergoes a radical shift.

That’s the case with Canada’s Skeena River, the nation’s second-largest salmon watershed, which until recently teemed with wild sockeye salmon. The salmon—who are vital to the food security of Indigenous peoples and wild animals, the prosperity of commercial fishers, and the transport of ecosystem-sustaining nutrients throughout the watershed—are generally thought to have declined moderately since the mid-20th century.

That estimate, suggests a new take on early-20th century populations, may be far too generous. “These analyses reveal century-long declines that are much greater than those based on modern era abundance data,” write researchers led by Michael Price, a biologist at Canada’s Simon Fraser University, in the journal Conservation Letters. But their paper isn’t just a lamentation; it may help inform, in the Skeena and elsewhere, efforts to bring them back.

Data collection on Canadian sockeye populations began in earnest after 1950. Early in the 20th century, however, fisheries scientists had collected scales from salmon caught by the Skeena’s burgeoning commercial fishing industry. Price and colleagues conducted genetic analyses of the scales, developing a DNA fingerprint for fish from each of the Skeena’s 13 subpopulations.

By combining that data with fisheries records and information on the number of fishing boats operating there throughout the 20th century, the researchers reconstructed the historical abundance of sockeye in the Skeena. They determined that present populations have dropped by between 56 and 99 percent, with each subpopulation affected.

That’s a far greater decline than suggested by reference to mid-century abundances. Using those, only 7 of the 13 sockeye subpopulations seem to have experienced a decline.

According to the new analysis, just one subpopulation is still abundant. That’s due largely to its supplementation by hatchery-raised salmon, and further masks the watershed’s plight. “Without humans and human resources,” says Price, those hatchery-raised fish “would not survive.” And because only one subpopulation is healthy, stability offered by the so-called portfolio effect—in which the decline of any one group is offset by continuing health of others—has been lost.

Price and colleagues hope their analysis will guide ongoing efforts to restore the salmon. Shifting perspective “back to a time before they incurred significant losses from commercial fisheries,” they write, “expands our understanding of the production potential of populations that can inform status evaluations and rebuilding discussions.”

In other words, people shouldn’t set their sights on mid-century levels. Those were already depleted. They should aim even higher. The potential is there—and that’s likely true not just for Skeena sockeye, Price says, but for other salmon species in other regions.

“We have fished them hard and altered their habitat for more than 100 years,” he says. “They no doubt are more diminished than we realize.”

Source: Price et al. “Genetics of century‐old fish scales reveal population patterns of decline.” Conservation Letters, 2019.

Image: Oregon State University

About the author: Brandon Keim is a freelance journalist specializing in animals, nature and science, and the author of The Eye of the Sandpiper: Stories From the Living World. Connect with him on Twitter, Instagram and Facebook.