Why go to the expense when they could just shoot them?
If they are going to go to the expense they should ship them to Africa where they are native instead of dumping them in other countries where they will be an invasive non native animal.
Probably edible, too. ‘Ell, if gator is tasty (tastes like chicken, of course) then hippos will be.
It is an invasive species. Kill it, fer crikie sakes.
I shoot the hippopotamus
With bullets made of platinum
Because if I use leaden ones
His hide would surely flatten ‘em.
-Hilaire Belloc, “The Bad Child’s Book of Beasts”