The sea, however, belonged to no one--maritime law did not develop until the 17th century. Most fishing fleets served only the village or a regional market, but one area had international significance: the herring fleets of the Baltic Sea.
The fish were salted and shipped all over Europe. Remember, Europe gave up meat for Lent (40 days) and for every Friday. Fish was the standard substitute, and only salted fish could be preserved.
The herring trade was one of the foundations of the power of the Hanseatic League. The fleets themselves were a kind of joint venture, with costs being spread across multiple investors. The associations formed were never permanent; once the harvest was in and the fish sold, the investors received their take and the partnership was over. They might reform the following year, but the mix of investors might be different.
The captain and crew were hired, though captains usually also had a share in the profits and was an investor. Crew members could invest, too, if they had the money. After the season, the crews went home and worked their farms or labored in the Hansa towns. It was not a business that lent itself to strong guilds.