From Arthur Palmer’s blog:

Lot 33 A boomerang of New Holland Captain James Cook 1728-1779, in Christies upcoming auction (Sale 7652 Exploration & Travel Sept 25 2008) purports to have been collected on Lieutenant Cook’s first voyage. This, if so, is no doubt a wonderful thing.

Without prejudice however, on viewing the item and also Lot 34; the two associated clubs with similar provenance, it would appear to be a wondrous happenstance. Perhaps even a hopeful and long bow to pull?

On balance the possibility and probability that any of these three artifacts were handled by Cook would seem to require an unsafe and uncritical leap of faith.