You just need to watch it to know the truth
In the end credits, it says: "All attempts were made to make sure no animals were hurt during the making of this movie." A laudable statement, to be sure.
But really, look at it. I watched it recently with my 12 year old daughter who had loved it when she was 5 or 6. Near the beginning, there were some sequences that were quite obvious that no animal that small could survive. She denied it. By the time the cat went over a waterfall in a basket while the dog was fighting a bear, she started crying and admitted that this was genuinely an animal snuff movie.
Yes, it was shot in Japan in the early 80's on a private island in Japan which acted as an animal reserve. It was governed by no laws, conventions or animal rights. I am sure the man who made it had a tremendous regard for animals, but it is also patently obvious that he was more interested in finishing his film...no matter how many cats and dogs it took.
I mean...just look at it. Use your common sense. My 12 year old did.