Make sure you opened the gate first. Then go to the second lock mechanism. When you do a back jump towards the metal rod, don't wait until it fully moves.
When it is at about 45 degrees, jump and grab the ledge nearby.
Since the door is now open, you can also reach a thin pole and swing across.
Get to the other side of the gate and grab the ledge there.
Use the higher pole to swing across.
And the Killer Whale Bottlerelic is there for you to pick.
