Unfortunately...

It takes no mathematical genius to see the factors of twelve. And every twelve years the migrations do coincide. In the Great Migrations the massed whales leave tens of thousands of square kilometers of devastation in their wake, devastation from which, because of following lesser migrations, the routes barely recover before the next Great Migration. Erosion is phenomenal. The monsters, subject to no natural control other than that apparently exacted by creatures we called mantas, were destroying the continent on which our employers operated.

Ubichi Corporation had been on Camelot twenty-five years. The original exploitation force, though equipped to face the world's physical peculiarities, hadn't been prepared for whale migrations. They'd been lost to a man, whale supper, because the Corporation's pre-exploitation studies had been so cursory. Next Great Migration another team, though they'd dug in, hadn't fared much better. Ubichi still hadn't done its scientific investigation. In fact, its only action was a determination that the whales had to go.

Simple enough, viewed from a board room at Geneva. But practical implementation was a nightmare under Camelot's technically stifling conditions. And the mantas recomplicated everything.

My flight leader's wagging wings directed my attention south. From a hill a dozen kilometers down the cable came flashing light, Clonninger Station reporting safe arrival of a convoy from Derry. For the next few hours we'd have to be especially alert.

It would take the zeppelins that long to beat north against the wind, and all the while they would be vulnerable to mantas from over the Gap. Mantas, as far as we could see at the time, couldn't tell the difference between dirigibles and whales. More air cover should be coming up...