Nice to finally meet another Englishman on these boards, Mortis!
First of all, let me say you've done a sterling job. I love the concept of a seawolf, and your decision to make it an animal, rather than a magical beast is just what I would have done. Even though it is, effectively, a hybrid creature, seal and wolf doesn't really seem that weird of a mix to me. You could tell me that that was a real creature, and, if I didn't know any better, I'd believe you.
And as for the greater and lesser varieties, you have my respect and awe, by merely showing that you know how the work the lycanthrope template without breaking off and having to lay down on the sofa with a tea towel over the lampshade, as I do.
However, I do have one minor constructive criticism, and that is that the Skills for your seawolf seem to be a little off. This may sound a bit rich, coming from me, the undisputed master of 'off stats', but bare with me. Your creature has a Swim skill of +10. However, seeing as it is basically a slightly modified wolf with a swim speed, which is, in itself a 2 Hit Die animal with an Intelligence score of only 2, it baffles me as to where these 10 'extra' skill points come from.
You might want to include something like this in it's Skills section, just underneath it's +4 racial bonus to tracking by scent.
Seawolves have a +10 racial bonus to Swim checks. A seawolf can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.