As we began our day, autumn slipped to winter. This event wasn’t much noticed in the warmth of La Paz, the capital of Baja California Sur, Mexico, where National Geographic Sea Bird docked along the waterfront. It was a day to celebrate, however, as now daylight increases in the northern hemisphere, renewing life with the approach of spring. And celebrate we did when we had the opportunity to observe and swim with the planet’s largest fish–the whale shark