Like Wilks mentioned...
Most of the breeds mentioned are likely to come out on the short end if a kicking Beaver gets a chance to grab on....no place for a Springer, AWS or Boykin, And a waterlogged Beaver will test the retrieving weight limit of all three. It may take a Kangal...
I'm with Battue...Use enough dog. I would not send any of my springers to retrieve a beaver and an AWS or Boykin isn't any bigger/tougher. I'd vote chessy or a lab. Years ago I had a chocolate that didn't care if something had feathers or fur. If I shot it, she was going to get it. Took an incidental deer while duck hunting one day. While it wasn't my intent to use the dog, she ran into the brush and held onto it for a close finishing shot. Wouldn't chase fur unless the gun went off.
ETA- There's some posts somewhere about a guy hunting seals for tablefare. I think it was Norway. Anyhow he snipes seals from the beach and uses a lab to retrieve them. Said that you couldn't send the dog until they were dead or they'd kill the dog.
