Complex sentence: Formerly abundant throughout the North Pacific, its range was limited to a single, isolated population on the uninhabited Commander Islands by 1741 when it was first described by Georg Wilhelm Steller, chief naturalist on an expedition led by explorer Vitus Bering.
Split into simpler sentences: Formerly abundant throughout the North Pacific, its range was limited to a single, isolated population on the uninhabited Commander Islands. It was first described in 1741 by Georg Wilhelm Steller, chief naturalist on the expedition led by explorer Vitus Bering.