Nope, not a gaff. Billman's got the right track here. I've seen this tool sometime in the past, but I can't remember where, or what it was used for. The handle is very distinctive.
The Japanese tuna workers are definitely using exactly this hook. The trouble is that tools migrate, not only from country to country, but from trade to trade (a lot of ceramics tools began as food preparation tools). Not to mention that peasant tools often became weapons, especially pole arms. Because Japanese armor was laced together, this hook would have been useful to pull riders from horseback...
Where did your cousin find it? Were there other tools there as well?
