You might find some argument about that when there is a lot of money involved, here was a previous controversial find on the bottom of the ocean

http://www.bbc.com/travel/story/20190908-a-shipwreck-worth-b...

In the UK there is some dispute about 'finders keepers' in any case, there was a case last year where a couple of guys got jail time for stealing a hoard

https://www.bbc.com/news/uk-england-hereford-worcester-50516...