Complex sentence: Before habitat destruction, the threats presented by introduced species, and overfishing, they could run much larger, with fish over thirty inches reported, especially in the strain present in Heart Lake in the southeastern portion of Yellowstone National Park.
Split into simpler sentences: Before habitat destruction, threats presented by introduced species, and overfishing, they could run much larger. There has been fish over thirty inches reported, especially in the strain present in Heart Lake in the southeastern portion of Yellowstone National Park.