Liveaquaria says 360 gallon MINIMUM for sharks and 180 gallon MINIMUM for rays. Seems a little small to me for something that can get 3' long but I know nothing about them. LA is my go-to for recommended minimums.
I would say 300-500 gallons minimum . I had a 8’ long 500 gallon and later a 8’ long 300 gallon. Although they were both monster tanks, I still couldn’t imagine a shark or ray being happy in them. I have always felt like they belonged it huge public aquariums. Just my 0.02.