Fishing has a long history in northern Europe. Even around the year 1900 one million tons of fish from the North Sea had been landed. However, when fishing biologists first undertook the huge task of gathering data on the frequencies of individual fish species round about the beginning of the 1800s, and when frequency studies of other species, such as deep sea dwellers, marine mammals and sea birds finally got underway in the twentieth century – very little was known about the characteristics of marine eco-systems prior to the onset of commercial fishing – or what the far-reaching or long-term consequences would be for eco-systems as a result of the intitial phase of commercial fishing. Both from an ecological and historical perspective, this lack of knowledge has proved extremely damaging. Knowledge about historical eco-systems is one of the critical factors for the sensitive modelling of existing eco-systems. Similarly, the growing political discussion about the introduction of marine protected zones necessitates viewing ecology within an historical perspective. From an historical viewpoint, the near absence of marine resource considerations in the historical material represents a serious shortfall. While terrestrial resources (especially agriculture, forestry work and mining) have been seen as meriting much attention over the last hundred years of research activity, conversely, marine resources have not been deemed as warranting the same degree of research attention. This imbalance has clear consequences for a coastal nation such as in Denmark, when history fails to reflect the importance of the sea.