Shipwreck License
A Shipwreck License is needed to fish in SS Whiskey, SS Minefield and SS Graveyard. It costs 50,000 gold and is good for 500 shipwreck scuba trips. If you are caught by the Coast Guard with an expired Shipwreck License, you'll have to pay double (100,000 gold) to renew it.
Note that Deckhand trips and being taken on trips by your friends in the area count towards using the license. Be especially careful if you have deckhand bonuses or deckhand vouchers activated.
How to get it[edit]
Travel to SS Whiskey and follow the first few instructions in Shipwreck Explorer Spoiler Tutorial
Using it in chapters[edit]
If you are on one of The Story of Shipwreck Explorer chapters, the very first time you pay the 50,000, it will read "Renew your Shipwreck License 250 more trips to be safe...". You can then fish that many times before you are given the option to renew. You still will have a possible 500 trips though. When you are in the renewable period, the notice will say that you should "Renew NOW".
You will also get a message showing you a percentage for Valid that will increase up to 100% at which it will be invalid.