Complex sentence: Fraga saw his credibility damaged in late 2002, when the oil tanker ship "Prestige" sank off the Galician coast causing a massive oil spill that affected the shoreline in the northwest of the region.
Split into simpler sentences: Fraga saw his credibility damaged in late 2002, when the oil tanker ship "Prestige" sank off the Galician coast. It caused a massive oil spill that affected the shoreline in the northwest of the region.