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A Natural History of Pacific Salmon

by Jim Lichatowich
Fall 2003

Native Americans called them "lightning following one another," large silver fish that flash like lightning as they leap through white water and over falls, or leap for no other reason than an exuberant display of strength and energy. Salmon are a powerful physical, ecological and cultural force that once exerted its influence around the Pacific Rim from Kyushu Island, Japan, to San Diego, California. How they attained that power is a story that unfolded a long time ago.

About 25 million years ago the North Pacific Ocean began to cool. Over 15 million years, as it cooled 18 degrees Fahrenheit, its productivity increased. About this time, and we are not sure exactly when, ancestral salmon living in freshwater lakes and large, slow rivers began to explore other parts of their aquatic world through short migrations. Eventually they reached estuaries, where they made short feeding forays into the brackish waters. Through the inexhaustible patience of evolutionary tinkering, the salmon evolved salt pumps in their gills that allowed them to make the plunge from brackish to full-strength seawater. In the cool North Pacific, the salmon gorged themselves on the rich oceanic pastures. After a year or more in the sea they returned to their home rivers, grown to a size that dwarfed their freshwater cousins. At this point, the salmon were fully anadromous; they spawned in freshwater but, as juveniles, migrated to the sea, where they fed for a few months or for as long as five or more years before returning to bury their eggs in the gravel of their home stream.

Anadromy had enormous consequences. The salmon's enhanced size and strength powered them upstream against swift currents and over falls, allowing them to reach the headwaters of rivers around the Pacific Rim. In some cases they migrated up to a thousand miles from the sea. They penetrated the landscape so thoroughly that, in the words of writer Tim Egan, "the Pacific Northwest is any place a salmon can get to." Large female salmon carried more eggs and buried them deeper in the gravel, reducing vulnerability to predators and death from the mechanical grinding action of gravel during high flows. In the larger watersheds the salmon's abundance exploded into tens of millions.

Large ocean-fed salmon migrating upstream in the millions are a major ecological event, a biological recharge of the energy circuits of ecosystems around the Pacific Rim. At least 22 species of mammals and birds feed on salmon carcasses, from brown bears to tiny winter wrens. The salmon's decomposing bodies release nutrients, enhancing aquatic food webs that nurture the next generation of salmon. Salmon carcasses pulled from the river by bears decompose, and the nutrients find their way into the cedars, Douglas firs and salmonberry. The spirit of the salmon gives strength to the giant Douglas firs, soars in the feathers of eagles, and prepares the young salmon for their long, dangerous journey. Japanese researcher Takeshi Murota says that by transferring energy from the ocean to headwaters, the salmon cast a large nutrient shadow over the landscape of the Pacific Rim. The mass transfer of nutrients is an important basis for biodiversity in all the lands facing the North Pacific Ocean, Murota says. Today, that shadow has thinned. Compared to a century and a half ago, depressed salmon runs in the Pacific Northwest now deliver only 6 to 7 percent of the nitrogen and phosphorous to the region's ecosystems.

About the Author
Jim Lichatowich is a fishery biologist and has spent the last 30 years working on Pacific salmon conservation. Since the listing of Pacific salmon under the federal Endangered Species Act, he has served on four independent scientific panels looking into the status and restoration of the salmon. Jim's recent book, Salmon Without Rivers, is a history of the Pacific salmon crisis.