We found the (same?) bird twice on February 17 and 18 2012. Both times on the beach west of Akhfennir, were large numbers of Lesser Black-backed, Yellow-legged and Audouin's Gull roost. It's was roughly at 28° 5.036'N 12° 5.896'W but observers should just stop several times on the main road leading from Akhfennir to Khniffis Lagoon, walk to the beach (ca. 200m) and check the gulls. That's how we found the bird twice. When it flew off, it fed with other gulls around a fishing vessel offshore.
I didn't go out to Khniffis lagoon by boat after finding this bird, so the ca. 5 very distant large black-backed gulls seen there remained unidentified. But several birders met before (who went out to the lagoon by boat/Feb. 2012) couldn't find any Kelp Gulls but up to 10 Great Black-backed Gulls.