[Paul Ward]

Hi jeeprasr and thanks for your comments. You've answered the how-so-big, but I was inteerested in the "why now?", why not ever in the past?

I guess the answer is tied up with the need for so much food requiring such long journey's a high metabolic rate and the need to be a warm blooded mammal to be so active in frigid waters. A question of which came first, the requirement to enter frigid waters to support the food requirement or the being warm blooded and large enough (as a result of enough food) to be able to enter frigid waters.

Then again, seals can do it too - while feeding on krill, and they are much smaller.