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Salmon Without Rivers
A History Of The Pacific Salmon Crisis
By James A. Lichatowich
ISLAND PRESSCopyright © 1999 James A. Lichatowich
All rights reserved.
Before the Endangered Species Act; before shopping centers covered streams with asphalt; before dams and dynamos harnessed the energy of wild rivers; before irrigation sucked rivers dry; before timber harvest robbed rivers of their protective forests; before fishermen's nets swept through the rivers and bays; before humans walked across the Bering Strait and into the Pacific Northwest; before glaciers gouged out Puget Sound; before the Oregon coast migrated away from Idaho; before all this, there were the salmon.
In the Linnean system for classification of plants and animals, the Pacific salmon fall into the family Salmonidae and the genus Oncorhynchus, the Pacific salmon and trout (Appendix A). The name "Oncorhynchus," from the Russian term for "hooknose," refers to the hooked upper jaw that males develop during mating. There are seven species of Pacific salmon within the genus Oncorhynchus. Five are found in North America: pink (O gorbuscha), chum (O. keta), sockeye (O nerka), coho (O kisutch), and chinook (O. tshawytscha). Two are found only in Asia: masu (0. masou) and amago (O. rhodurus). Pacific trout within the genus Oncorhynchus include the anadromous steelhead, O. mykiss, and sea-run cutthroat trout, O. clarki. The five species of Pacific salmon and the two anadromous trout have evolved a rich array of life histories and local and regional distributions, which are summarized in Appendix B.
Native Americans sometimes called the salmon "lightning following one another," a name that evokes an image of the large silver fish flashing through swift water. Our culture's most common image of the salmon is of a fish climbing the face of a seemingly impassable falls, wiggling and fighting for purchase to launch another jump. We associate the salmon with a strong, fighting spirit and an unstoppable determination to return to the stream of their birth to create the next generation. Our image fosters the belief that the salmon possess an inherent ability to persist regardless of obstacles. But their persistence is more than just legend. Nature and, more recently, humans have repeatedly created conditions that threatened the salmon's survival, yet they have persisted.
All organisms are historical phenomena, and the salmon are no exception. For thousands or even millions of years, the salmon have accumulated the history of their species and retained it in the gene pools of individuals and populations. As a result, the salmon's genetic program, coded in its DNA, is a textbook containing thousands of years of evolutionary experience—lessons on how to survive in a harsh, changing world. That the Pacific salmon have survived our largely unrestrained assault on them and their habitats over the past 150 years proves the value of the lessons each salmon carries in its genes. And it is precisely because the salmon are such tough, persistent animals that their catastrophic decline in California, Oregon, Washington, and Idaho is so tragic. Once we understand the salmon's story, we can see their collapse as a clear testimony to the failure of our management institutions and to the rapid and massive habitat destruction over the past century. To fully appreciate the salmon's resilience, we must understand their evolutionary history and the episodes of cataclysmic environmental change they have survived.
A Rough Trip through Evolutionary Time
The Pacific salmon belong to a group of fishes whose branch on the evolutionary tree sprouted relatively late, about 400 million years ago. Within a short 40 million years these newcomers, the ray-finned fishes, came to dominate many freshwater habitats and were well on their way to dominating the sea. The ray-finned fishes comprise three main groups, and each achieved prominence for a time. Sturgeons and paddlefishes are the surviving members of the oldest group, and the gars give us a glimpse at the second group. Teleosts are the last and still prevalent group, which includes familiar fishes such as salmon, trout, perches, pikes, and catfishes. The fossil record shows that teleosts arrived relatively late in western North America. They did not dominate western fresh waters until about 55 million years ago.
Teleosts, like the other fishes before them, rose to dominance because they evolved improved structural and physiological features that gave them a competitive edge. The teleosts acquired a more efficient respiratory system, and their body form and musculature changed to permit more rapid and complex movement—important survival traits for both prey and predator. Among these efficiently designed fishes is the family Salmonidae, which contains salmon, trout, whitefishes, graylings, and ciscoes.
No one knows just when the Salmonidae split off from other ancient teleost fishes, but the family might be 100 million years old. That means ancestral salmon could have swum in the same waters used by dinosaurs during the last few million years of their reign on earth. The earliest confirmed Salmonidae fossil is Eosalmo driftwoodensis, whose bones were found in Eocene sediments of British Columbia (Appendix C). It resembled the modern grayling and lived in ancient lakes of western Canada about 40 to 50 million years ago. Based on the fossil record, Salmonidae's prehistoric range in western North America extended as far north as the Yukon Basin (66° north latitude) and as far south as the Lake Chapala Basin of Mexico (31° north latitude).
Native fish fauna in the Pacific Northwest survived a rough trip through evolutionary time. No other region in North America has been as geologically active as the Pacific Northwest, which means no other region has experienced the same degree of habitat and environmental transformation. Mountains rose, the coastline migrated, the climate changed drastically, and volcanoes flooded large areas of the region with thick layers of molten lava. Many fish species—pikes, freshwater catfishes, bass, sunfish—did not survive the monumental geologic and climatic changes. But the tough and tenacious salmon endured, and their resilience is still a source of hope for the future.
Origins of Anadromy
Salmon are anadromous. Adult salmon spawn, their eggs incubate, and juveniles rear for a few weeks to several years in fresh water. Then the juveniles migrate to the saltwater sea, where they spend a few months to several years before returning to their home stream to spawn in fresh water and repeat the cycle. For about a century, scientists have debated whether the salmon originated in fresh or salt water; the weight of the evidence now suggests a freshwater origin. Paleontologists have found fossils of ancient trout only in freshwater sediments, and the bones of primitive salmonids such as the graylings and whitefishes are found only in fresh water (although some graylings may enter estuaries). Since the extinct members of the family and the older existing Salmonidae reside exclusively in fresh water, we can conclude, tentatively at least, that the salmon's life in the rivers and lakes goes back further in time than their life in the ocean.
What advantage did the salmon gain by crossing from fresh to salt water and back? Whatever the advantage, it had to outweigh heavy physiological costs, because moving from fresh to salt water puts tremendous stress on the fish and requires much preparation. Before entering the sea, the salmon change from stream-dwelling parrs to smolts, a transformation that involves physiological and behavioral adaptations to the saltwater environment. For example, when a parr becomes a smolt, it increases the purine and guanine in its scales. As a result, the young salmon's natural camouflage, which is well suited to hiding in a stream, gives way to a uniform silver on its sides and undersides—a coloration better suited to life in the sea. Because oxygen concentrations are lower in sea water, the salmon smolt must also produce a different, more efficient hemoglobin to cope with the decrease in oxygen. Furthermore, salt pumps in the gill membranes must reverse. In fresh water these pumps prevent dilution of plasma electrolytes, but in salt water the pumps must keep electrolytes out to prevent concentration above normal levels. In addition to the physiological changes, the salmon must undergo major behavioral changes. Life under an overhanging bank in a small stream is quite different than life in the ocean, where the habitat is open and predators abound.
Migration across the fresh-saltwater boundary occurs in two distinct patterns. Anadromous fishes, such as the salmon, breed in fresh water and then migrate to sea to feed and mature. Catadromous fishes, such as the eel, breed in the sea and then migrate to fresh water to rear and mature. Anadromous fishes are found most often in northern latitudes, while catadromous fishes are found most often in the tropics. In the mid-1980s, biologist Mart Gross and his colleagues looked at these patterns and discovered an important clue to the anadromy puzzle. The clue turned out to be food. In northern latitudes the oceans are more productive than the adjacent fresh waters, but in southern latitudes the reverse is true. Apparently, the Pacific salmon abandoned fresh water to rear in the more nourishing oceanic pastures of the northern latitudes.
This makes sense in the framework of evolutionary time because the oceans off the Pacific Northwest were not always as cold and productive as they are today. Prior to the Oligocene epoch, about 40 million years ago, the oceans were 10°C (about 18°F) warmer and therefore probably less productive. Then about 25 million years ago, they began to cool, reaching their current temperature regime about 8 million years ago. As the seas cooled, their productivity increased. According to current theory, the Pacific salmon developed anadromy to take advantage of this richness.
The salmon grew rapidly in the oceans, and their larger size at maturity improved their fitness in the rivers of the Northwest in at least three important ways. Anadromous salmon could produce more offspring because the larger females carried more eggs to the spawning grounds. Furthermore, the larger, stronger fish were more able to muscle their way over falls or through strong currents, extending their distribution throughout the Northwest's network of rivers. Finally, with their greater bulk, the salmon could dig deeper redds, giving greater protection to their incubating eggs.
Anadromy also benefited the rivers of the Northwest. The migration of large salmon into the interior of the Northwest was, in effect, a mass transfer of nutrients from the sea upstream into the headwaters. Those nutrients fertilized the less productive river ecosystems, increasing the growth and survival of juvenile salmon.
If the salmon did originate in fresh water, then the hooknose probably developed anadromy in stages beginning during the late Oligocene, when the oceans started to cool (Appendix C). The current fossil record can prove only that salmonids similar to extant anadromous species lived in coastal rivers at least 10 million years ago. Confirming an older origin for anadromy will have to wait until fossils are found in Oligocene sediments in sites with access to the sea.
Upheavals and Eruptions
Biologists believe the ancestors of the modern salmon were lake dwellers because fossils of the earliest salmonids are usually found in fine-grained sediments associated with lakes or slow-moving, low-gradient rivers. According to this hypothesis, the early Salmonidae colonized interior lake systems, where they lived in isolation and evolved a rich species diversify. By the late Miocene (about 10 to 15 million years ago), however, salmonid fossils appear in coarse gravels, suggesting that the ancient fish expanded their range into the high-energy habitats of rives. According to the current fossil record, Oncorhynchus, the genus containing the Pacific salmon, probably emerged at this time.
The most remarkable stream-dwelling salmonid from this period is the now-extinct saber-toothed salmon (Smilodonichthys rastrosus). This formidable six-foot-long fish had a pair of enormous, curved breeding teeth, but despite its ferocious appearance, it fed primarily on plankton, much like the modern but smaller sockeye salmon. Fossil remains of the saber-toothed salmon have been found in coarse gravels, indicating that it spent part of its life in riverine habitats of central Oregon and coastal California. Its bones have been found along with other Oncorhynchus fossils that resemble the modern coho salmon. Since a diet of plankton suggests lake or ocean rearing habitats, S. rastrosus likely used the rivers only for spawning. Judging from the location of the fossils found in central Oregon, the saber-toothed salmon probably spawned in the Columbia River watershed.
When the bones of the earliest salmonid, Eosalmo, settled into lake sediments in British Columbia 40 to 50 million years ago, the coastal mountains of California, Oregon, and Washington lay submerged beneath the Pacific, and the ocean's waves washed beaches near the Idaho border. A series of volcanic islands broke the sea's surface well offshore between the future states of Oregon and California. Those islands would later rise and become part of the Klamath Mountains. The landscape of the northern California and Oregon coastal mountains began to take on its current form about 12 million years ago,.
Anyone traveling U.S. Highway 101 along the West Coast would view the coastal mountains as stationary, but in geologic time the coastal ranges undertook a migration no less spectacular than the migration of salmon. Fifteen million years ago, the Oregon Coast Range, which hugged the western edge of the Cascade Mountains, rotated out and 32° north to its present location. As the coastal mountains rotated and uplifted, rivers kept pace by downcutting or eroding their channels through the rising land. By the Pliocene, about 2 to 5 million years ago, the coastal rivers had cut their catchment basins into the drainage patterns we see today. The formation of the Cascade Mountains also influenced the development of rivers in the Northwest during this same period. Runoff from these peaks enabled a few large rivers—the Fraser, Columbia, Umpqua, Siuslaw, Rogue, Klamath, Sacramento, and Chehalis—to erode rapidly enough to maintain their connections with the interior regions.
If the hooknose came into existence before the mountains rose and the coast shifted to its present position, as hypothesized, then the early members of the genus had to survive millions of years of cataclysmic habitat disruption. For example, one consequence of active mountain building and river downcutting would have been landslides large enough to block streams or create impassable waterfalls. Mountain building would have resulted in a continuous round of habitat destruction and creation. Individual populations of salmon would have become extinct when they were cut off from their spawning habitat or when their habitat was rendered unlivable. At the same time, stray salmon would have colonized new habitats, and the process of adaptation would begin again as new populations took hold. Local extinction balanced by recolonization on an evolutionary time scale has long been an important survival mechanism of the Pacific salmon.
While the coastal rivers cut watersheds out of the rising western edge of the Northwest, farther east the earth opened and spilled lava over the gently rolling hills of interior Oregon, Washington, and British Columbia. Between 12 and 17 million years ago, massive flows of hot lava moving at twenty-five to thirty miles per hour repeatedly covered the land. Each successive eruption entombed salmon habitat with a layer of lava 100 feet thick and set the ecological clock back to near zero. Rivers had to erode new channels, soils had to re-form, and plants and animals from outside the region had to repopulate the barren landscape.
The ancient lava flows of the Columbia Basin are clearly visible today as basalt, especially where rivers have cut through and exposed the individual strata like layers of a gigantic cake. Two of the most spectacular such exposures can be seen in the canyon of the Grande Ronde River in eastern Oregon, and along the seventy-two-mile gorge of the Columbia River. The lava flowed into and plugged the ancient Columbia River, forcing it to move north and cut a new channel. Since then, the Columbia has remained in its present channel.
By about 2 million years ago, watersheds in the Northwest had carved their current drainage patterns (Figure 1.1). Genetic analysis of the Pacific salmon suggests that the modern species evolved from three ancestral lines around this time. The first two diverged a little more than 2 million years ago; one produced rainbow trout, coho, and chinook salmon, while the second yielded sockeye salmon. The third line diverged about 1.25 million years ago, giving rise to pink and chum salmon. According to this analysis, if the hooknose came into existence during the Miocene, these fish underwent 10 million years of evolutionary development before the appearance of the ancestral lines that produced the modern salmon.
Stabilized watersheds and the appearance of modern species did not signal the end of the cataclysmic changes for salmon. A period of intense glaciation soon followed and drastically altered the region's climate, rivers, and salmon habitat, especially in coastal Washington, Puget Sound, and the Columbia River Basin.
Excerpted from Salmon Without Rivers by James A. Lichatowich. Copyright © 1999 James A. Lichatowich. Excerpted by permission of ISLAND PRESS.
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