This big male-type Caspian Gull has relative long legs with longer tibia compared to argentatus. The small darkish eye is situated closer to the flat forehead than in argentatus and the colour is relative dark with a slight green peppering in the iris. The bill is relative long and without pronounced gonys angle. It has a good cachinnans jizz with high push up breast, flat belly slightly dropped behind legs and long elongated slim rear. Additionally the upperparts are slightly darker than nearby argentatus. P5 has been shed during moult, but the amount of black on p10 is spot on for chachinnans with all white feather tip and grey tongue extensive on especially inner web. The white apical spots are all extreme small due to wear.
Note the adult Yellow-legged Gull just behind to the right of the Caspian Gull in the two photos above and the two just belove. Look at the differnces in bill length and structure with the long, sleder bill of cachinnans in contrast to the strong and heavy bill in michahellis