The Coast Range Association Salmon & Survival Why Native and Hatchery Salmon are Different

SURVIVAL OF THE FITTEST

Salmon and steelhead have lived in the Pacific Northwest for 40 to 50 million years. When ice covered much of the landscape, their range was smaller than today. But when the ice retreated some 12,000 years ago, salmonids returned to their old territories, their spawning migrations transferring the best of the sea back to land in rivers from Mexico to Alaska.

In geological time, salmon and steelhead are winners. If evolution is survival of the fittest, salmonids are among the fittest creatures on the planet. To show just how fit, author Richard Manning compared the salmon life cycle - emerging from the egg to returning adult weighing up to 40 pounds - to a more familiar one on land. He said that if cows grew like salmon, an Alberta, Canada, rancher could release calves at 200 pounds each, let them range unattended and free for a few years as far south as Texas and Oklahoma, and then on a given date see a fraction of them return to her front gate weighing 50,000 pounds each. (Woody, 1999)

How Have Salmon Survived?

The salmon and steelhead survival strategy is to lay large numbers of eggs, few of which survive to adulthood and return to spawn. But those survivors have faced and survived massive obstacles between the gravel of their birth and the gravel where they lay their future. Salmonids also have developed a tremendously successful life-history strategy and the survivors spread the genes that code for those successes to subsequent generations.

Wild salmonids adapt quickly to changing environments, sometimes in just one to three generations. This improves their ability to survive as long as they can draw on the vast resource of genetic diversity within each population. Over millennia of returning faithfully to a particular stream, native genes code for characteristics that perfectly match the range of environmental fluctuations in it. Each river's native population, also called a "deme," contains among its members a rich diversity of genes that allow some individuals to survive almost any catastrophe that might occur in the river's watershed.

For instance, Oregon Coast Range salmon adapted to systems where large disturbances like floods and storm-driven landslides regularly occur. Snake River runs evolved to thrive on a journey of hundreds of miles through rain forest, desert and mountains. The paradoxical combination of direct adaptation to a particular stream, as well as the diversity of adaptations within the population, serves as a hedge for the local deme as a whole - a hedge against rains that come early or late, against high or low stream flows, against germs in the water.

The genes that survive to thrive are those that work best given the range of changes that are usual in a particular stream or river over the salmon's millennia of experience there. These variations can take the external form of size or shape of adult bodies, the coloration of returning adults, how old they are when they return and even the behavior the fish exhibit. And it is generally believed that even if we do not know what good those differences do, evolution found a reason for it. Eric Taylor of the Zoology Department at the University of British Columbia in Vancouver says "a pervasive notion is that this variability is not due to environmental noise [i.e., is not random], but reflects something that is meaningful to the survival and persistence of a population in a local environment." (Grant, 1997)

These different traits within a population give some individual salmonids an edge in particular environmental circumstances. Further, the more fish there are in a parent generation, the greater the number of variations in the succeeding offspring - the greater the diversity, the greater the chances for successfully meeting new environmental challenges and the greater chance for the deme as a whole to survive.

"Natural selection ensures the success of a species by favoring reproduction among animals which are adapted harmoniously with their environment, and by eliminating those not so well adapted. Every river system is different. It imposes physical and biological constraints on the animals developing within it, which differ in subtle ways from those imposed in other rivers. Hence the pressures of natural selection differ between rivers, and it is therefore not surprising to find that the genetic composition of the salmon population in one river differs from that in the next. This close match between genotype [the particular pattern of genes in an individual] and the environment is preserved efficiently through high homing precision, so that these stocks remain discrete. So the stock of salmon of a particular river is likely to possess a genetically determined range of patterns of development, tailored by natural selection, which ensure success in that specific river." (Thorpe, 1988)

Maintaining that variety of gene-based traits is critical for survival. "Steelhead and salmon have evolved with major ocean climatic fluctuations - and they have survived and flourished because of a diversity of life histories that have allowed for adaptation to a wide variety of environmental conditions. Preservation of the many different life history types of wild steelhead and salmon is essential for their future survival, and for the future generations of anglers that will pursue them." (Pearcy, 1999)

The prestigious National Research Council looked at the needs of salmonids in a 1996 publication, Upstream: Salmon and Society in the Pacific Northwest. The authors concluded that preserving and restoring Northwest salmon runs depended on "maintaining appropriate diversity in salmon gene pools and population structure," a subject, they said, "which has not been adequately recognized." (National Research Council, 1996)

The diversity of local adaptations is crucial. When the environment of a particular stream changes - at least makes changes that are within salmon's millennia of adaptation to that stream - some of the fish in a particular year's run will die. But others carry genes allowing them to survive and thrive in the changed environment. That's what diverse genetics in a population allows.

Some fish return from the ocean a year earlier than the rest of their cousins, some a year later. That buffers the run as a whole against one or two years of unfavorable stream conditions. Differences in when young fish leave their streams for the ocean also spreads the risk of potentially unfavorable habitat conditions.

As runs get smaller, however, this genetic protection of the species is reduced. Fewer fish mean fewer different traits. The run returning to a changed environment will have fewer individuals that can thrive in that new environment. This puts stress on the stock that ultimately it may not be able to survive.

We all know that salmon and steelhead numbers have plummeted. Nearly one third of the salmon runs that covered the Pacific Northwest when Europeans arrived here are now extinct. Most remaining runs are officially facing extinction; even the healthiest runs are at risk from human activities.

Humans have fouled salmon streams, over-harvested in the ocean and dammed off historic habitat for decades. But one of the most destructive things humans have done is to build hatcheries that tinker with salmonids' proven risk-spreading strategy. That tinkering has directly changed and substantially reduced diversity within individual demes. Those changes and simplifications have made it harder still for salmon to hang on.

Comparison of Wild and Hatchery Alsea, OR, Coho
PERFORMANCE	WILD	HATCHERY
Juvenile Mortality	6.5%	21.9%
Smolt to Adult Survival	2.9%	1.9%
Spawning Time	Late December	Late October
Disease Resistance (Fall Cr. Syndrome)	High	Low
Marine Distribution	South to Cal.	Oregon Coast

Source: Oregon Dept. Fish and Wildlife, 1983

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