The Ability of Salmon to Change and Survive

Jonathan Weiner’s Pulitzer-Prize winning book The Beak of the Finch articulates the remarkable strides that have been made in the science of evolution in recent decades. While the most exacting studies have been done on the Galapagos Islands, researchers throughout the world have documented how the physical characteristics of species, carried in their genes, rapidly change to optimize the species for survival as their environments change. Mr. Weiner concludes that Darwin “vastly underestimated the power of natural selection. Its action is neither rare nor slow. It leads to evolution daily and hourly, all around us, and we can watch.”24

Biologists have not yet determined just when the seven races of Pacific salmon evolved. Some argue that because Pacific salmon (the genus Onchorhychus) are restricted to the Pacific, and the Pacific was connected to the Atlantic during the late Pliocene era, the salmon race must have originated as recently as 500,000 to 1,000,000 years ago. Others, using DNA testing techniques, argue that the species may be two to three million years old.

But the salmon that we now protect as endangered evolved much more recently. As recently as 12,000 years ago, a tiny moment in geological time, there were no Columbia Basin salmon. Glaciers blocked the Columbia River as North America's last Ice Age was ending. When the ice melted, the salmon began to colonize the Columbia River Basin, and were highly successful at doing so. Other species, like the sticklebacks common in Canadian lakes, were also isolated and formed different “species” within the last 12,000 years.25

About 800 years ago, a three-mile chunk of Table Mountain fell into the Columbia River, blocking it entirely.26 This event probably cut off the upriver tribes from salmon entirely until the river broke through and the salmon came back.27 No one knows whether the blockage lasted for one, two, three or more salmon generations. There is some chance that the salmon recolonized the upper Columbia and Snake Rivers within the last 800 years. In 1913, the Fraser River was temporarily blocked when blasting unleashed a rock slide that reportedly killed millions of sockeye salmon.28 Yet Fraser River sockeye recovered and remained abundant for decades.

It may be that salmon runs in the Snake River have always been subject to occasional disappearances. A 1938 researcher reported that “[w]hen running, the [salmon in the upper Snake River] were sufficiently abundant to supply all who could take them. The main limitation on them was their occasional failure to run and the restricted number of convenient fishing places.”29

Where conditions are favorable, salmon can colonize available habitat at an amazing rate. Chinook salmon from California were introduced into New Zealand at the turn of the century. Without heavy commercial fishing pressure, the salmon spread to run in five New Zealand rivers. And, more significantly, there are demonstrable differences in appearance between the different salmon runs. The authors of one study of the New Zealand salmon concluded that

“. . . skeptics of the application of the species concept (including the U.S. Endangered Species Act) to salmon populations might argue that the rapid diversification of salmon populations indicates they they are more plastic than has been assumed, and that only a diverse gene pool need be preserved, not every spatially and genetically discrete population.”30

This “plasticity” is not a phenomenon unique to New Zealand. Recently, a race of spring-spawning chinook salmon has developed in the Great Lakes, which developed from a fall-spawning race.31 In the language of genetic biologists, the genus Onchorhychus has extraordinarily plastic genes.

Although salmon are famous for returning to their natal streams, they also stray and return to the wrong stream or even the wrong river. Biologists retrieving coded wire tags in Alaskan rivers have been known to recover Columbia River salmon.

Straying is useful for the preservation of the species, in that the stray salmon form the nucleus for new colonies of salmon in previously unused habitat. When people have introduced salmon to new places, straying allows salmon to spread rapidly to colonize available habitat. The eruption of Mt. St. Helens provided yet another example of the value of straying: when returning adults from the Toutle River found the the river completely blocked by ash and debris, they were able to change course, go to the Cowlitz River, and spawn there.32

That salmon are adaptable does not mean that we should make things worse for them. But as Gregg Easterbrook emphasized in his call for “ecorealism”, A Moment on the Earth, “understanding the strength and resiliance of life helps us put the environmental issues of the day into a perspective larger than our own. Without such perspective, humankind will not be able to make rational choices regarding which environmental alarms are genuine and which merely this year’s fad.”33

There is some evidence that it is difficult to replace a population of salmon once extinguished, but the evidence is generally limited and anecdotal. Between 1949 and 1975, for example, Canadian fishery managers tried and failed to replace sockeye in the Adams River, a tributary of the Fraser River that had been blocked by a dam from 1908 to 1921.34

Some biologists believe that populations of salmon have highly specific adaptations to particular habitat that interfere with efforts to “transplant” salmon, but the evidence is sketchy.35 This belief, however, is a cornerstone of the prevailing salmon orthodoxy. Bruce Brown’s influential Mountain in the Clouds: A Search for the Wild Salmon, went so far as to claim that juvenile salmon genes were, in essence, unique to the particular stream in which they are born.36 Journalists and politicians commonly repeat claims that once salmon are lost from a single river, particular salmon traits are “never to be recovered”.37 This perspective exaggerates the differences in genetic materials and ignores the rapidity of evolution in salmon populations.

24 J. Weiner, The Beak of the Finch 9 (Vintage 1994).

25 Id. at 185.

26 R. White, The Organic Machine: The Remaking of the Columbia River 10 (Hill & Wang 1995).

27 Id. at 18.

28 R. Steelquist, A Field Guide to the Pacific Salmon 31.

29 J. Steward, “Basin-Plateau Aboriginal Sociopolitical Groups Bulletin 120 (Smithsonian Inst. 1938), quoted in “Compilation of Information on Salmon and Steelhead Losses in the Columbia River Basin”, Appendix D of the 1987 Columbia River Basin Fish and Wildlife Program, at 64 (NWPPC Mar. 1986).

30 T. Quinn et al., “Origin and Genetic Structure of Chinook Salmon (Oncorhynchus tshawytshcha) Transplanted from California to New Zealand: Allozyme and mtDNA Evidence” 18 (research conducted under contract to Puget Power, in press as of 1996).

31 M. C. Healey, in Pacific Salmon Life Histories, at 382.

32 R. Taylor, "Conservation Biology", Wana Chinook Tymoo, Issue One, 1996, at 30 (CRITFC); cf. R. Steelquist, Field Guide to the Pacific Salmon 42 (“When the Toutle River salmon returned to the river, they found it choked with ash and silt, abandoned it, and spawned instead in the Kalama River.”)

33 G. Easterbrook, A Moment on the Earth 45.

34 NRC, Upstream at 135 (Prepub. ed.).

35 Uncharacteristically, the NRC’s Upstream report cites no studies at all in support of its assertion that there is “strong evidence” that genetics explains “complicated homing behavior, temperature adjustments, unique local mating behavior, and adjustments of smolts to local feeding conditions”. Upstream at 134 (Prepub. ed.).

36 B. Brown, Mountain in the Clouds: A Search for the Wild Salmon 62.

37 J. Cone, A Common Fate 124.

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