So I want to just say that it's not always true if the habitat supports them that they will be or should be there. Louisiana is a prime example of how that does not fit. We were the muskrat capitol of the world with more muskrats than any other state and likely the top 4 states below Louisiana would have to combine to have matched our then robust and godlike muskrat population.

We smashed them for so many years, that really truly we hardly have any population of them left. When I say godlike population, we were taking 4m-6m every year for YEARS, and then we introduced nutria and started killing all the beaver again. It's all been downhill since then, but it's aggravating. I too have all the books that exist for raising muskrats because of this purpose. Some of the guys have only ever trapped 1 muskrat here in LA due to how rare they are, and it sucks because they should be all over the state. They are not though and are absent in 95% of the state now.

https://www.amazon.com/Successful-Muskrat-Farming-Robert-Hodgson/dp/B000UD43SW

there is other books out there as well. most from the 30's

I've trapped and they were moved to a marsh. Hava-hart live trap and catch a female and have 5 or six live traps besides her...the noise and squaking will bring them out. That many males build new huts and channels so they get established fast

About 14 years ago a friend of mine asked me to bring him a few live muskrats so he could release them in a pond on his property. I was only able to bring him three that were alive in foothold traps. Simply released them into five gallon buckets and quickly snapped the lids on. A few months had gone by and I asked him how things were going with the rats. He said they were staying in the pond and he would see them swimming around. Mind you, his pond was already established for years. We sorta lost touch after that so I have no idea if they bred and multiplied or what.

When nutria arrive, the rats disappear!!

The beaver not being abundant in places without great wetlands also puts the muskrats population at risk. I dont know if they can dam up things like beaver but I do know they rely on beavers to make their habitat.