Gull vs Skua

Great black-backed gulls tend to be the toughest shore birds until the bonxies, great skuas, turn up for the summer. I was watching a skua on the water from Scapa pier as it fed on a dead bird (which it may well have killed) and wondering if GBBs ever challenge the skuas when one such gull swooped out of nowhere and started really attacking the skua. First time I have seen this. The gull is on the skua in the main shot and the skua is escaping in the extra.