England, Ireland, France and Germany were repeatedly ravaged by climate related famine during the late 13th century. This meant that trade in food products were big, especially to regions of need. (That was, of course, if those regions had products to exchange in return).
The Hanseatic League took advantage of the famines. They became a major food ressource for the Baltic region as they were a very productive fishery especially for herring. They were productive because of changes in distribution and preservation. One of the important changes was at about 1350. It was the adoption of salting as a method for preserving barrels of fish for long shipment or storage.
However, the climate of northern Europe was too cool and wet for the right amount of salt required for fish preservation so the Hanseatic League traded fish for salt with countries near the Mediterreanean, where salted fish products were in big demand