I don’t know if this or something similar has been requested before, so sorry if yes...
How about a fish-crate, which you can sell to the Hunter's Call? If empty, you can't sell it...there has to be at least one fish in it. Selling it through the crate gives you extra 20% of gold and rep.
You can find those crates washed ashore, or you can find messages in a bottle which let you claim such a crate from the Hunter's Call. Those voyages' requirements, to finish it, are at least 10 fish in the crate and at a certain seapost to deliver, for this you get extra 50% of gold and rep.
What would change if this got added?
People would fill that crate with fish, they will keep it for longer to fill it with more fish, due to the more gold and rep. This would lead to more sold (and stolen) fish, because it won't sink with the ships supplies.
What do you think of this?
