IIRC the native americans used trash fish and fish waste in the corn hills (they planted in clumps aka hills instead of the rows we use nowadays, and I think the saying was a fish per hill). I suspect that they had dogs, and were well known as hunters to the wildelife which kept the bears, raccoons, and skunks out of their plantings with fish waste. Unlike today, when most wild predators have little or no fear of people.
I suspect the fish provided a lot of N, but also smaller amounts of P and K (most fish emulsion is around 5-1-2) plus calcium from the bones, but that might not have been available for a while.
The ground becoming hard after the fish is a puzzle. There are a few things which can cause that (high Mg, lack of OM and a few others), but putting a few fish in there would not seem like enough to greatly change any of those factors, at least not more than in a small circle around each fish. That change may have had more to do with the clearing of the land and other prep. It would be interesting to get the details on that soil, the analysis of it (ideally before and after but that’s unlikely) and how it compared to the surrounding soils.
