On the very bottom right corner ofThe Island map, the open sea leads into a small island full of trikes, pteranodos, stegos, Paras and Ankylo. In the water in the middle you will likely find an Itchy and when you start the tame they only seem to swim to the other side of that pond (a 10 second swim away) and never into the open sea. Just because the water leading into it is full of Megalos, so it might take a while to get the Itchy back safely.
I tamed one of these named Diana. She was super fast but kind of stupid: always getting stuck on something. Diana and I formed somewhat of a relationship as time went on. Our bond strengthened she was able to beach a shark for me to kill it. Diana soon became one of my best friends... but nothing lasts forever. As I was leading her back to base via SS Dodo, I noticed a large figure swimming rapidly towards us. Diana made the fatal mistake of not paying attention to her surroundings. I helplessly fire arrow after arrow at it, but it was so filled with rage that they had no affect. I had to watch as MY Diana was ripped to shreds by an oversized fish. That is why my base is now called Fort Diana in honor of the brave soul. Thank you for your time.