The Pacific Northwest is one of the most geologically active regions in North America. Major geologic events have periodically caused massive restructuring of rivers and aquatic habitat during the past several million years. Mountain-building processes created the Cascade, Coast, and Olympic Ranges, cutting off rivers except those that could downcut fast enough to keep pace with the rising landscape—the Columbia, Sacramento, Rogue, and Klamath Rivers, for example. The earth has repeatedly opened and spewed rivers of molten lava over large areas of the Northwest, filling river channels and lakes and setting the ecological clock to near zero. Glacial ice sculpted large areas of the landscape, especially north of the present city of Olympia. The repeated floods of molten lava are clearly seen stacked like layers of a cake in the walls of the Columbia River Gorge. Volcanoes are still active. The eruption of Mount St. Helens in 1980 showed clearly how geologic events can impact salmon habitat.

Superimpose onto these geologic events changing climate patterns at time scales ranging from the millennial to the decadal and annual. For example, following the melting of the ice after the last glacial period, the Pacific Northwest baked under a very hot dry climate that lasted several thousand years. The cool moist climate that we now enjoy arrived about four thousand years ago. Scientists have recently identified a forty-to-sixty-year pattern of climate change that can have pronounced effects on the productivity of the ocean. Various attributes of climate vary from year to year, such as seasonal temperatures and the amount of precipitation. Geology and climate interact in ways that influence salmon habitat. The western slopes of mountains are wet, whereas the eastern slopes can be very dry.

Many fish originally native to the Northwest, such as pikes, freshwater catfishes, bass, and sunfish, were unable to adapt to all these changes and became extinct, but the salmon persisted.

The combination of unstable geology and climate fluctuations created a complex mosaic of continuously changing salmon habitats—a diverse array of physical habitat types embedded in a fluctuating environment. Rivers of all sizes and lengths flow through the complex landscapes, continuously rearrange their channels, rebuilding, shifting, and maintaining the basic structure of salmon habitat. The interaction between the surrounding landscape and the natural seasonal flow patterns produces a chain of habitats, reaching from the lowlands and estuaries up to the headwaters in a continuum of connected places where the salmon can spawn, rear, and migrate. From the salmon's perspective, the watershed is a riverscape of salmon-friendly places, where survival is high, and other places where survival is low. The survival peaks and troughs are always changing, much like the ever-changing peaks and troughs of the sea. Salmon respond to the survival peaks and troughs in the riverscape through their life histories. Life history is simply where and when the salmon carry out important life functions such as migration, rearing, spawning, and incubation during their life cycle.

Each species has a characteristic life history with unique attributes that separate it from the other species. Some of those attributes are their age structure (when they mature and spawn), their length of freshwater residence, and their spawning and rearing distribution and timing. The spawning distributions of the different salmon species clearly show how they use life history to partition the watershed and make the most of the available habitat. Pink and chum salmon generally spawn in the lower stream reaches. Coho salmon spawn in the upper smaller tributaries, whereas chinook salmon make use of the middle and lower mainstems or larger tributaries. Sockeye salmon spawn near lakes where the juveniles rear. However, these generalized life histories are really central themes of the species, around which the individual populations have evolved a rich diversity in response to local habitat conditions.

The great salmon biologist William F. Thompson gave us a clear visual image of salmon life histories and their close relationship with habitat when he described them as "a chain of favorable environments connected within a definite season in time and place, in such a way to provide maximum survival."1 Within a given river system there may be a bundle of several of these life-history chains. For example, in a single population some juvenile spring chinook salmon may remain in their headwater spawning areas for an entire year and migrate to sea in the spring of their second year of life. Other juveniles from the same population may—shortly after emerging from the gravel—migrate to the lower reaches of the river, where they grow rapidly, and then migrate to sea in the summer or fall of their first year. Some spring chinook salmon may migrate out of the upper headwaters in the fall and hold in the lower mainstem through the winter before migrating to sea in the spring of their second year. There are several other variations on these freshwater life histories.

Life-history diversity achieves two important purposes. First, it allows the salmon to use all the habitat in the river; and, second, it protects the population from catastrophic environmental fluctuations. Multiple life histories are how the salmon avoid "putting all their eggs in one basket." Following a catastrophic environmental event such as a severe drought, some of the salmon—following one or more of the many life-history pathways—will always survive. Life-history diversity is how the salmon solved the problem of survival in fluctuating environments and changing habitats. It is an important legacy of their evolutionary history.

The salmon's life histories are what bind them to their local, co-evolved habitat. In undisturbed rivers, each salmon population is composed of a bundle of several life histories, several alternative survival strategies or pathways through the riverscape. Unlike the salmon raised in a hatchery environment with its feedlot regime, salmon in a natural population in a healthy river do not all do the same thing in the same place at the same time. Wild salmon maximize the number of different pathways they travel through the time and space dimensions of their habitat. As the riverscape changes due to natural disturbances (fires, floods, droughts, and so on), some of the salmon's life histories are in survival peaks, while others drop into troughs. Historically, even though their habitat changed in response to natural disturbances and climate fluctuations, the salmon's multiple survival strategies allowed them to remain so productive that they provided a reliable base for the Pacific Northwest Indians' economy—an economy that sustained itself for several thousand years.

This point cannot be overstated. Life-history diversity is an important legacy of the salmon's evolutionary history—it's how they survived in a harsh, changing environment. Life-history diversity is not just an archaic historical curiosity—it's the long-ignored key to the salmon's recovery.

As soon as settlers arrived in the Pacific Northwest, they began rearranging the rivers of the Northwest. One by one, the life-history pathways through the riverscape disappeared, or became death-traps as the habitat complexity was homogenized and simplified. Irrigation dried up the lower reaches of rivers, cutting off salmon migration through the summer months. Grazing eliminated riparian vegetation, causing stream temperatures to rise. Logging and splash damming destroyed the natural habitat structure and complexity of forested streams. Hatcheries stripped away diversity while molding the salmon to a uniform sameness that fit their factory-like operations. Dams eliminated spawning and rearing areas and migration corridors. Excessive harvest also reduced the salmon's biodiversity. Even our habitat restoration activities reduced habitat complexity and the opportunity for the salmon to maintain life-history diversity.

In many rivers of the Northwest, salmon spawning and juvenile rearing are now confined to small areas in the headwaters. Migration is restricted to a narrow window in spring. Life-history diversity—the complex array of pathways through the riverscape—is gone, leaving the salmon one or maybe two survival strategies. The effect of this loss of diversity is most evident during periods of natural stress, such as prolonged drought or changing ocean conditions. The current massive plunge of salmon into endangered-species status is the result of changing ocean conditions superimposed on populations that have been severely weakened by a loss of life-history diversity.

Since the arrival of Euro-Americans, the development of rivers and their surrounding landscape has continuously eroded the life-history diversity of the region's salmon populations. But it was not just the development of the industrial economy. The very agencies that were charged with the protection of the salmon have, through their programs, also whittled away at the salmon's biodiversity. Fisheries managers produce giant schools of domesticated salmon that migrate to sea and return to spawn at the same time. These herds of uniform salmon released from hatcheries have been spawned by the vision of a controlled, simplified river and ecosystem where the salmon are often allowed only one survival strategy, which we have picked for them. The recovery of salmon will be thwarted until at least some of the natural pathways through the riverscape are restored, until we give life to the ghosts of those salmon life histories that were once present in healthy rivers.

To restore these salmon ghosts we will have to pay attention to the entire watershed. Too often we have focused our attention on the remaining salmon and their life histories, which are largely restricted to the upper watersheds. Those last refugia need to be protected, but if we are to restore abundant and sustainable salmon populations, we need to restore their life-history diversity, the multiple pathways through the watershed. To do that we will have to focus on the entire watershed, and restore the entire chain of favorable places, from the headwaters to the estuary. We will have to learn to respect the salmon and the wisdom in their genes, the lessons of survival they acquired during their rough trip through the geologic history of the Northwest.

Jim Lichatowich is a fisheries biologist and author of Salmon Without Rivers, a history of the Pacific salmon crisis.

To order a copy of OREGON SALMON: Essays on the State of the Fish at the Turn of the Millennium (from which this essay is excerpted) call (503) 222-9091 or email info@ortrout.org