About 15-20 minutes or 10 km east of Eocheong Island (ca 60 km WNW of Gunsan City), a large, heavy-billed gull was picked up following the wake of the boat. After 2-3 minutes it headed off towards a fishing boat, before returning to follow the ferry again for 2-3 more minutes, until we turned to enter the harbor.
Difficult to see well and even harder to take images of in the heavy overcast it nevertheless appeared very long-winged, and gradually plumage details could be made out as it came closer: largely white-headed, though with a small dark eye-patch setting off obvious white eye-crescents; a dark patch on the nape sides, and size larger than Slaty-backed or Vega Gulls in direct comparison. As it flew low across the water, it also revealed a clearly grey mantle with contrasting white rump and tail, and an obvious, complete black terminal tail band. The upperwings showed very dark secondaries, with a grayish midwing panel marked off with whitish tips to the greater coverts, while much of the forewing, comprising the inner and median coverts, were much darker brown. As the bird picked up height and flew over the boat, the final key features could be seen: almost white underwings, with dark edges to the underwing coverts, an obviously darker trailing edge, and only a weak translucent blaze across the inner primaries.
All of these features, typical of first winter Great Black-headed Gull, had fortunately only recently become rather familiar - from a close encounter with South Korea's second ever GBHG, seen in Busan only 6 days before!