Complex sentence: Stocking and hatchery operations had had an overall negative impact on the Yellowstone cutthroat and Westslope cutthroat populations and in 1953 the National Park Service began closing the hatcheries and stopping stocking operations.
Split into simpler sentences: Stocking and hatchery operations ultimately negatively impacted on the Yellowstone cutthroat and Westslope cutthroat populations in the park. In 1953 the National Park Service began closing the hatcheries and stopping stocking operations.