Complex sentence: During the 1980s, at least two hundred and seventy ships passed through the Spratly Islands region each day, and currently more than half of the world's supertanker traffic, by tonnage, passes through the region's waters every year.
Split into simpler sentences: During the 1980s, at least 270 ships passed through the Spratly Islands region each day. More than half of the world's supertanker traffic, by tonnage, passes through the region's waters every year.