Complex sentence: The Storm Petrel breeds on exposed and uninhabited islands which it visits only to breed and always at night, otherwise frequenting mid-depth waters away from the coastal zone but not over the ocean deeps.
Split into simpler sentences: The Storm Petrel breeds on exposed and uninhabited islands which it visits only to breed and always at night. It otherwise frequents mid-depth waters away from the coastal zone but not over the ocean deeps.