Kill Plunder Beacons on the high seas. Turn in to black market person next to buc's den bank. Search forum post for plunder beacon and it should give you plenty of info on tactics used to kill them. The Triton is a reward so comes in statue form so you can sell them. The pet bonds when statue is used. A quick vendor search in game for one may show many for sale to buy with gold.
I wouldn't slack on doing the plunder beacons though if you are looking to collect the maritime cargo for them because it's a limited time event. An official end date hasn't been given but it will be done sometime this year (maybe by Sept).