What is one viable solution to increase the effective size and genetic variation in the grizzly bear population in yellowstone national park?

One viable solution would be to increase the food sources for the Grizzlies. This is because grizzy bears don't technically have predators, and are mostly hunted by people. However, they're less likely to be hunted in Yellowstone. 

By increasing the food supply, they will have an abundance of food, which will allow the population to successfully sustain more young, and increase the population.