Fark (of all places) linked up this New Scientist article summarizing some new archeological findings about an interesting change in medieval fishing habits:

James Barrett and colleagues at the University of York looked at fish bones, dating from AD 600 to AD 1600, recovered from a range of archaeological sites across Britain. To their surprise, they discovered a sudden and dramatic change in the intensity of fishing and the type of fish deposited at the sites in just a 50-year period, around AD 1000.

While the article tries to connect this strange development with modern over-fishing problems, I didn't really see the connection.