In Mexico, a cruise among critters

Our guide yelled, "In the water, now!" and 10 of us scurried to the swim platform, awkwardly duckwalking in our fins, holding masks and snorkels in place as we plunged into the dark ocean. Restless from the previous day's weather front, the sea rolled in great swells, lifting and scattering us like bathtub toys.

I quickly put my mask in the water, rotating to see beneath the surface around me. With a jolt I realized I was staring down the throat of a gigantic whale shark. Mouth open wide, she was feeding near the surface, filtering plankton through her gills. Slowly the 30-foot-long behemoth slid by me, aware of my presence but unconcerned.

As she passed, I got a close look at the remarkable camouflage pattern of stripes and spots on her massive gray body. Though she was as big as a whale, whale sharks are actually fish — the largest on Earth — reaching up to 60 feet long over a 100- to 150-year life span. Unlike other fish, they hatch eggs inside their bodies and give birth to live offspring. And, unlike other sharks, they have no scary teeth — which mattered a great deal to me at the moment. The only danger I faced was from her tail, which swept from side to side to propel her through the water.

By noon we were all exhausted, having fought the waves to swim with five different whale sharks. As we settled back on the boat, a curious 10-foot-long baby stuck its head out of the water to take a long look at us. It was a fitting finale to an experience that was more thrilling and ethereal than we could have imagined.

The mother ship

Hopes of swimming with whale sharks had brought my friend and me to La Paz, Mexico, and the world-famous wildlife sanctuary in the Sea of Cortez. As anxious as we were to fulfill that dream, we anticipated other exciting "critter encounters" during our week aboard the 42-cabin Safari Endeavour, one of the luxury vessels in the Un-Cruise Adventures fleet. The ship had all the fun stuff we'd need: skiffs, kayaks, stand-up paddleboards, wet suits and snorkeling gear. And we assumed — rightly, as it turned out — that our fellow passengers would be as gung-ho as we are about wildlife, good food and drink, and the personal attention that comes with a 2:1 guest-crew ratio.

At the gated dock in La Paz we met the crew and quickly unpacked in our Commander Class cabin, with its twin beds, private bath, large windows and ample storage space. All of the Endeavour's accommodations are above deck, light and spacious, and some suites have private balconies.

As the ship got underway, we joined Capt. Barrett Whitten in the lounge for a Champagne toast. This area would become a favorite gathering spot with its wraparound windows, access to the bow viewing area, ever-present coffee and freshly baked snacks, and the amply stocked bar.

One deck below, windows lined the dining room at water level. During meals, our attention shifted from the cuisine to the antics of dolphins and seabirds outside. In no time, we became attached to the crew members waiting tables, who quickly learned our names and preferences.

'Galapagos of North America'

The narrow gulf, which formed when the Baja Peninsula broke away from mainland Mexico, is unique, a bucket-list destination for animal lovers. It's the youngest sea in the world, but with a rich history and even richer natural bounty. Marine explorer and conservationist Jacques Cousteau called it the "Galapagos of North America" and the "world's aquarium" with good reason.

The gulf and its islands are home to well over 900 kinds of fish, 40 reptile and amphibian species, about 200 varieties of birds and 500 desert plants. Many species are found only here, and are endangered.

The Endeavour sails the Sea of Cortez from November through March, when migrating creatures are in residence. Every month is special: whale sharks, blue whales, fin whales and elephant seals in November; humpback whales in December through March; and gray whales and sperm whales February through March. Dolphins, orcas, pilot whales and sea lions are here year-round. And then there are the avian residents, including the blue-footed boobies that many bird-watchers journey to the Galapagos to see.

Although the Sea of Cortez is remote and most of its islands are uninhabited, it hasn't escaped the ravages of man. Centuries ago, conquistadors decimated the oyster beds for the black pearls that existed only here. And commercial fishing interests still threaten the endemic species. However, since the establishment of the Loreto National Marine Park in 1996, the fisheries have rebounded and marine mammals have returned in abundance. Recreational visits like ours reinforce the tourism benefits.

The adventure

Our first full day aboard began with a spectacular sunrise over Isla San Francisco, a deserted island with a beautiful, seemingly untouched crescent beach. Later, the crew would shuttle chairs, towels, kayaks and refreshments to shore so we'd lack for nothing. Some passengers set off on a hike along the narrow spine of a ridge overlooking the cove, while we set off snorkeling from the beach. With visibility of 20 to 30 feet, we easily spotted needlefish, striped king angelfish, shy puffer fish, a gorgeous yellow-and-black Moorish idol and countless species we couldn't identify. The kayakers reported sighting of sea turtles and small stingrays.

During the Endeavour's repositioning run from Alaska's Glacier Bay to Mexico, the chef brought along Alaskan silver salmon, which topped the dinner menu that night along with roasted lamb loin and a Greek dish for vegetarians.

The following morning we dropped anchor in an idyllic bay at Bahia Agua Verde, where a few sailboats bobbed gently off another picturesque beach. We spent the morning kayaking in small coves beneath richly colored cliffs festooned with wildflowers from a recent rain. Pelicans and blue-footed boobies basked on the rocks and plunged into the water for fish. In the afternoon we mounted mules and followed a trail leading up the cliffs and into the arid wilderness, past a cemetery with markers showing hardy souls had lived here in the early 1900s.

On Day 4, as we explored the calm waters of Isla Danzante's Honeymoon Cove, a group of small, dark mobula rays erupted from the water near us and skimmed along the surface before belly flopping with a smack. Theories abound as to why they do this, but I think they're just having fun pretending they're birds as well as fish. At times in the Sea of Cortez hundreds of them will "fly," causing humans in their midst to feel as if they're in a popcorn popper.

Some belly flopping was going on among the paddle boarders, too, but they were having as much fun as the rays, and the boards were great for bird- and fish-watching. We spent the afternoon snorkeling, and discovered a large colony of sea stars with brilliant neon colors and patterns. Nature trumps clothing designers any day.

Toward the end of the week nature sent us a weather front. In the dining room, the sea crashed against the windows and the breakfast menu changed from eggs Benedict (rough seas and boiling water make for a hazardous kitchen) to safer scrambled eggs.

Unfortunately, surf was also pounding the coast of Los Islotes, where we had planned to swim among young sea lion pups, members of the colony that lives there. The weather reminded us that the Sea of Cortez is an unpredictable marine wilderness, not Disneyland. Rolling decks are part of the adventure, but there are calm harbors at hand if it gets too rough.

Ultimately, on our last full day aboard, the sea calmed enough for us to swim with whale sharks, fulfilling a lifelong dream.

Dale Leatherman is a freelance writer and former president of the Society of American Travel Writers. She lives in West Virginia.