Web Exercises

Managing Columbia River Salmon

Until about a century ago, up to 16 million salmon and steelhead trout migrated every year up the Columbia River system to their breeding grounds in small headwater streams and lakes. Both native people and wildlife in the Pacific Northwest depended on this prodigious bounty. For a few months each year, there were more fish than anyone could eat. The runs were probably never uniform, however. For reasons that we don't fully understand, the number of fish returning from the ocean often varied widely from year to year.

Dam building, logging, urbanization, pollution, overfishing, and a host of other human activities have caused disastrous declines in the salmon fishery over the past century. Total numbers are down nearly 90 percent from historic highs, and only about one-tenth of the fish in the river are now wild stocks; the rest are hatchery-reared.

Look at the a graph of salmon runs, below, and read about salmon in the Pacific Northwest at http://www.mhhe.com/apps (Look for the essay "Salmon runs in the Columbia River.")

1. Why do you think salmon catches were so low in the 1870s? Were salmon scarce then? What is the difference between the maximum salmon harvest and the closest low point on the graph?

2. Cycles of maximum and minimum salmon runs are not uniform in periodicity or amplitude, but if you were asked to give an estimate of how frequently big runs occurred, what answer would you give?

3. Cover up data on the graph for years after 1935. If you had been a fisheries manager in 1935, what would you have predicted about the abundance of fish in the next 10 or 20 years, based on previous history?

4. How would you design an experiment to determine which of the factors mentioned in the essay about salmon had the greatest effect on their demise?

5. Do you think that there was any hope, when seines, traps, and set nets were prohibited in 1950, that the salmon would ever return?