This is a map of English eel-rents and payments from the late 10th century through the 17th century. Much of the Doomsday-era data is taken from the data collected and made public by John Palmer and the Hull Doomsday Project.
Any eel-rent noted as having one eel due represent a place where the record is unclear about the number of eels due (such as the rent due for the mill at Wolvey in 1251, which called for the mill to pay 1/2 of all the fish and eels caught there to Ivo de Dene). In each of these cases, the actual number of eels due almost certainly exceeded one.
Hovering over any single location will provide you with basic information about the eel-rents from that place. Clicking on a location will call up a more thorough account, including notes and citation information. You can toggle centuries on and off through the menu at the side.
If you have trouble with the imbedded map, you can find a larger, non-imbedded version here.