In the 1970s, their numbers were up to 60,000. But this cannot continue forever. One growth rate is self-limiting and is called logistic . Initially, the growth rate is rapid as there are unlimited resources. But as numbers increase, food and other resources per individual decline.
Death rates increase, and eventually a stable population is reached.
The species have reached their carrying capacity and no further growth is possible. In fact, the situation is certainly more complex, with births and deaths fluctuating about a mean value. Populations for Chinook salmon. The population of salmon swimming upstream mirrors the flow rate in the rivers, with a three year offset. Modern Extinctions Population vs. time when humans arrived in the continent.