Question

The table below shows the salmon population, in thousands of pounds, in Columbia River, from 1870 to 1950.

Answer 1

Answer:

Between 1931 and 1950

Explanation:

This is most likely the time period during which a series of large hydropower units were built on the Columbia River. When we look at the record of the salmon population in previous years, we notice that the population increased steadily, even if at different rates, between 1870 and 1931. However, we can see that from 1931 to 1950 the population decreased by two thirds. This is most likely the result of some event that disrupted the ecosystem of the salmon, such as the hydropower units that were built on the river.

Answer 2

Between 1931 and 1950, since hydropower units disturb fish habitats and would cause a decrease in fish populations/birthrates.