https://www.sciencedaily.com/releases/2018/07/180723071611.htm

"The practice of transshipment -- refrigerated cargo vessels meeting with fishing boats at sea to exchange seafood, crew, fuel or supplies -- is common in many fisheries as it enables fishing vessels to remain at sea while their catch is taken to market," says Dr Nathan Miller of SkyTruth, USA, who led the study. "However, it lacks uniform regulation and transparent data. This hinders sustainable fisheries management as it makes it very difficult to monitor the amount of marine life being taken from the sea."

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.