Possible South Polar Skua?

This interesting Skua has been photographed during a pelagic trip I organized, on the 16-09-2011 off Fuseta/Algarve. My special thanks to Michael Southcott, who has joined this trip together with two friends, for sharing this and other pictures with me.


Large Skua Stercorarius sp about 5 miles off Fuseta (Algarve, Portugal) 16-09-2011. Photo: Michael Southcott (click photo to enlarge).

The uniformly whitish, "frosty" body, sharply contrasting to a very dark/blackish underwing, together with a relatively small, all brownish head, lacking the "cap" of an (adult) Great Skua Stercorarius skua, makes this a candidate for a South Polar Skua Stercorarius maccormicki (intermediate phase?) in my opinion.
The species is known to winter in the North Atlantic with regularity (pdf) and has been recorded in early September this year in Spanish waters (3 Ind. off Lanzarote and 1 Ind. at Estaca de Bares, Galicia, NW Spain) well documented on the blog of one of the observers here, as well as on Ricard Gutiérrez' website "Rare birds in Spain".

This is not the first "suspicious" Great Skua I am seeing here, but the first one that has been captured in a picture. I am not experienced with this species (I guess relatively few people are...) and lack certainty here, so I would be interested in any opinion on this matter. Field identification seems to be often difficult in this species and a different moulting cycle (reversed, being from southern hemisphere) and pattern (shorter moulting phase, replacing 3 primaries at once) in the species, often pointed out as a reliable criteria, is questioned to be that reliable here.

Is this bird still in the range of Great Skua Stercorarius skua ? Just a slightly aberrant "whitish" Individual ? But I never heard of a "pale morph" on Great Skua... Further, since no moulting is visible and together with the lack of the "cap" of an adult/subadult Great Skua, this has to be a bird before the first immature moult (takes place from December to February on Great Skua) = a fresh juvenile, in case it is "just" a Great Skua. But are not juvenile Great Skuas clearly rufus brown, with somewhat lighter "spots"? And finally, is it possible to identify this bird based on this photo at all ?