https://phys.org/news/2018-07-vessel-tracking-exposes-dark-side.html

The lack of consistent regulation enables illegally caught fish to enter the market. It also creates the opportunity for other illegal activities relating to drugs and even people.

"Some human rights abuses have been associated with transshipment. By allowing fishing vessels to remain at sea for months or even years at a time, captains are able to keep their crew at sea indefinitely, resulting in de facto slavery," say Miller.