TL;DR - the observed reduction of the elk herd correlated with wolf introduction, but also with an increase in cougars, grizzly bears, and even bison, all of which either reduce or compete with elk. Human hunting also added pressure, but that has been limited as the herd size reduced. It is complicated.
https://www.nps.gov/yell/learn/ys-24-1-the-challenge-of-unde...
TL;DR - the observed reduction of the elk herd correlated with wolf introduction, but also with an increase in cougars, grizzly bears, and even bison, all of which either reduce or compete with elk. Human hunting also added pressure, but that has been limited as the herd size reduced. It is complicated.