With the end of kapu (1815-20), when the old Hawaiian social system broke down, many young men were left without a position in the society. The crown (Hawaiian government) let contracts on employment of these men. Although the contracts were for specified periods, some did not return; others merely boarded ships that needed crews and are not included in written contracts or other records of their departure.
The archives in Honolulu have some of the records on the contracted Hawaiians.

Echoing Guest David Heller, there are many stories to be told; we will never know them all.
The Gold Rush country attracted Hawaiians who were not contracted there; some left Hudsons Bay Company (or had already left them), some joined who had stayed on with the cattle industry, and still others either jumped ship or worked passage there. It will be difficult to get accurate estimates of numbers; much of what we 'know' has been passed on verbally or as brief notes in journals.