By the time you discover this dino you should have a Basilosaurus, have it above Lv200 have your basilo with a strong saddle, clear waters off sharks and it's lower level mate, let your basilo sit above the plesi and start shooting.

Once down place 200 Neuro toxins

And your kibble, swim up to surface and wait for torpor to go down half, inject 80 neuros and go back up again, ride the plesi so you don't freeze to death and watch a movie, your tame will be ready in less than 50min.