there is a paper in the Atholl Papers (X46-9) dated 31 Jan 1755 giving permission for a J Tarbett to leave the Island (no other info I think but havn't actually looked at it) - I'd look for a marriage off island.
The Tarbet family I think would have been well researched (+ a fair amount of garbage) as a son of Will and Cath - Thomas - was a mormon emigrant from Peel
Willam & cath married 26Oct 1800 at St Peters in Peel WT could sign his name (Cath signed x) - the witnesses are no help being the almost compulsory Parish Clerk and church warden Wm Cannell they married by licence (again 99% did) and both were over 21 and both of the parish