[fuzzfactor]

Eels appeared to be an alternative currency, the kind that can be "minted" by a lot more individuals compared to precious metal coins or bank notes, and can circulate in excess of legal tender authorized or issued.

Most of the rents call for even numbers of eels, but the mentioned levy of "1/2 of all the fish and eels caught there" is more like a percentage tax. It does bring to mind the possibility that fully grown eels were probably all supposed to be about the same size so they were the standard of exchange, with the remaining catch being converted locally at a variable fish-per-eel rate depending on what those other fish were like.

The data's so sketchy it could have been anything, but something looks fishy about the 13th century. How did the number of eels due skyrocket so dramatically and then pipe down to a more representative trend the very next century? Especially considering that eel-based rents were a directly declining arrangement over the centuries.

Somebody needs to audit this, there might be some kind of currency exchange manipulation or insidious devaluation responsible.