Disclaimer: This is anecdotal. I had a healthy population of unwanted curly leaf pondweed in my SMB/YP/GSH pond. Two years after adding papershell crayfish, I had to look hard to find any pondweed. I did build a rock jetty for cover and released the crayfish next to it. The pondweed has not returned. I also tried to trap some crayfish near the jetty last spring and did not catch any.