I think I'd agree with you that it belongs to Colombia as they found it. How long can someone have rights to the ship? If you lose something and it is put in a "lost and found", there is a limited amount of time during which it can be reclaimed.

This is a wiki link about the book, Sahara: https://en.wikipedia.org/wiki/Sahara_(novel)

The plot is mostly based in the Sahara Desert which is where it gets its name.