It's been asked: (roughly) the same nutrition can be extracted from the ocean in Japan or in England. Why did the British Isles not develop a maritime diet and culture to the same degree that Japan did? Two answers come immediately to mind: the cultural center of Japan (southern Honshu and Kyushu) is warmer than Britain; and there is nothing like the sheltered inland sea in the UK. Even the Irish Sea or narrowest part of the Channel are often quite a rough go.
A new paper shows that fishing disappeared quickly after the development of dairy farming in the British Isles - but contrasts this against the cultures around the Baltic, where fishing and farming coexisted quite a bit more. The Baltic is colder than Britain but the water is more sheltered. So: cultures around a sheltered sea are more likely to develop a maritime culture, even if the water is colder.
5 hours ago