If you need to keep it in one place you can use dinos to trap it. Dinoes swim in space like they do in water so create cage of dinosaurs ( make sure they are big, heavy and have a lot of health because the astrodelphis

will attack your dinos ) then leave a gap for the astrodelphis to get in. Make sure all of your dinos are on passive and lead an astrodelphis in the cage by getting it's aggro. Once you have trapped it the astrodelphis will not be able to escape unless it kills or moves your dinos out of the way.

More Astrodelphis Taming & KO Tips