I don't think it's all that jerky. Actually looks rather fluid to me. Only when the tail switches directions does it look jerky. And if you need to know movements for animations, the best thing to do is study the genuine article.
http://www.oceanfootage.com/oceans/v...show_clipbin=1
Also, don't segment it. That would probably cause more harm than good. Slow the animation down, and notice how the tail of an orca tends to flail a little rather than staying stiff all the time. I am seriously amazed by this effort, though. Keep at it, man!