Andrew Isenberg's "The Destruction of the Bison" and Shepard Krech "The Ecological Indian" both blow this notion of the Indian out of the water. Indians a) killed for sport as much as for food; b) were depopulating the bison to extinction (just not as fast as the whites, but every bit as surely); c) thought---at least many tribes---that the bison were limitless becuase the "gods" sent them; and d) did NOT "use all of the buffalo" that they killed. They used EVERY PART of SOME buffalo, but it is a total myth that they used what they killed.
Trappers, settlers, missionaries all observed vast herds dead and rotting as a result of INDIAN hunts, not white hunters.
It is equally true that whites were far more effective and deadly, and did in a couple of decades what would have taken the Indians several decades to do---however, it was the WHITES who realized that the bison were going extinct, and, long before government got involved, PRIVATE farmers and ranchers began to collect and protect small herds of bison, saving them from extinction. Indeed, Yellowstone bought its herd from PRIVATE sources!!
Don't buy the myth that the Indians were "eco-friendly." It's not true.
PC B.S. They took as many as their primitive stone-age hunting techniques could get them. Up to and including setting the prairie on fire to drive whole herds off of cliffs. Whereupon there would be much rejoicing and gorging.