This taxon is Not Recognised as a species by BirdLife International.
Larus argentatus and L. smithsonianus (the latter including vegae and mongolicus) (del Hoyo and Collar 2014) were previously lumped as L. argentatus following Sibley and Monroe (1990, 1993).
BirdLife International (2016) Species factsheet: Larus argentatus. Downloaded from http://www.birdlife.org on 04/12/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 04/12/2016.