A Web of Relationships

BY JEFF RENNER

The salmon made sleep impossible. The splashing from their night-time migration through the shallow water just beyond my streamside tent was almost continuous. These determined fish had not eaten in the weeks since they left the ocean. Consider running an ultra-marathon after days of fasting, and you have an inkling of the power and endurance of salmon. To witness their migration is to witness an ancient convergence of life surrendered and gifted, a cycle that reaches beyond the dawn of our own species. Forty-million-year-old salmon fossils have been found in northwestern British Columbia; their ancestors include the saber-toothed salmon, which reached lengths of nine feet and, of course, the five smaller species of contemporary Pacific salmon: chinook, coho, chum, pink, and sockeye.

Straining to track a pair of salmon upstream in the darkness, I knew persistent splashing likely marked a female excavating a depression in the gravel streambed, creating a nest for her eggs that would soon be fertilized by a nearby male. The female then moves upstream, sweeping up gravel that will drift with the current to cover and protect the embryos. She dies soon afterward.

Perhaps 20 percent of the embryos will survive to become alevins. Unable to swim, they dwell within the gravel, subsisting on the lunch bag of nutrients within their yolk sacs. Emerging from the riverbed as fry, the developing salmon begin feeding on aquatic insects. As they grow to roughly the length of your hand and develop the ability to survive in salt water, the smolt enter the vastness of the Pacific Ocean, their body weight multiplying as they feed incessantly. The imperative of their biological clock eventually drives them to return to the river or stream of their birth, intent on producing a new generation. The timing, typically one to four years, depends upon their exact species.

The salmon who survive this journey are champions of endurance. Fisheries scientists estimate that for every 3,000 eggs laid, there are two adults who return to spawn. Human activity has become a threat multiplier, further diminishing their odds of survival. University of Washington scientist David Montgomery grouped these threats into what he termed the Four H’s in his book King of Fish (Basic Books): harvest, hydropower, hatcheries, and habitat.

The challenges confronting salmon in their struggle to survive as a species along the Pacific Coast have increased more in the last two centuries than in the preceding two million years. The magnitude and impact of the human-driven environmental damage is so great that it’s been referred to as geotrauma. A recently discovered form of rock called plastiglomerate has been held up as evidence of that trauma. A blend of plastic, sand, shells, wood, and seaweed, future geologists may use it as a fossil marker of human-driven environmental degradation.

The changes to the biosphere—the zone where life exists on Earth—are what make the determined grasp of salmon to life increasingly tenuous. These include changes in the temperature, chemistry, and movement of air and water.

One quarter of a million Columbia and Snake River salmon died before spawning in 2015. That was half of the expected migration. Water temperatures exceeded 70 degrees, increasing their susceptibility to infection and parasites and decreasing needed oxygen. In 2021, the Columbia River temperatures were even warmer. Underwater video revealed widespread fungal infections and lesions; huge clusters of salmon crowded into pockets of cooler water, desperate for oxygen; and salmon carcasses obscured warmer riverbeds nearby.