I recommend using a longneck rifle with tranqdarts. Headshots do more physical damage and less torpor. Aim for the sail and the neck. Use argent kibble. Second prime fish, third mutton. When tamed, use a quetzal with a platform saddle to transport it to base.
I had a Spino once. His name was J.J. I loved him. But like always, good things always come to an end. We were out looking for giant turtles for their keratin when J.J. fell over the edge of a cliff. I was on my pteradon so I flew over the edge and J.J. was following me back to bace when he was killed my a therizinosaurus... I just sat there on my pteradon watching him be torn apart, unable to help... So now, my bace is called Fort J.J. in honor of him. I will always remember my most loyal friend.
Ok so here is how I tamed my Spino. I had the help of my brother, so maybe bring some help just in case. All we did was find the nearest Spino, and I shot arrows at it to lure it out of the water so it wouldn't drown while unconscious. Then my bro shot a couple tanq arrows while i shot tranq darts. It took 2 hits from each to knock it out. So it was fairly easy for me. Good luck and I hope this helps.