From the deck of a boat a few miles off the coast of Ventura, the Pacific looks like the last wild frontier.

It’s a Saturday afternoon in mid-January, but the sunlight, unabated by trees or buildings, cuts the chill that clings like seaweed to the waves. It angles up and off the heavy sheets of water like pure, white light from a magnifying glass.

And if the Pacific is one of the few last wild frontiers — with those untouchable depths that cough up those unthinkable creatures — this boat is the saddle on which we wranglers are riding the unruly blue bronc beneath us.

This is life on the sea with Island Packers, an outfit that offers cruises, as well as whalewatching and island tours, to tourists and locals alike (the company is also the authorized concessionaire to Channel Islands National Park). Day-trippers and those en route to any of the five Channel Islands — namely Anacapa, San Miguel, Santa Cruz, Santa Rosa and Santa Barbara — for day trips or camping can board Island Packers vessels in either the Ventura or Channel Islands harbors.

Today, we’re on the lookout for gray whales, monumental and mysterious creatures that take annual sojourns through this spot off the southern coast en route to the warmer waters of Baja California, where they birth their calves. Like that of the castaways of Gilligan’s Island, ours is a three-hour tour. Well, almost. Ours is three and a half hours — and sometimes it’s that last 30 minutes that sends passengers right over the edge and into the waiting, condescending arms of sea sickness.

“If you’re going to lose your lunch, don’t go to the bathroom,” a deep, jovial voice announces over a system of well-placed speakers as the boat pulls out of Ventura Harbor. “If you’re going to lose your lunch, go to the back of the boat, bend down and pretend that you’re looking at some passing fish.”

This announcement is followed by chuckles (mostly nervous chuckles since, funny as it is, no one wants to be the schmuck at the back of the boat donating his or her lunch to passing sea life).

No, this is the day of the island adventurer, the would-be Cousteau, the lover of great gray, freakishly huge water creatures. By freakishly huge, we’re talking 45 to 50 feet long and about 40 tons — or 80,000 pounds (gasp!). Gray females are larger than the males, which is the case with all baleen whales — whales that basically suck mud off the ocean floor and use special plates in the mouth to sift for edible tidbits. The grays and other baleens eat large quantities of very small sea species, like tube worms and crustaceans, according to the American Cetacean Society.

They may technically be bottom feeders, but the grays are no slouches: They take one of the longest migrations of any mammal, with annual 10,000 to 14,000-mile round-trip migrations, according to the American Cetacean Society. The whales start leaving the feeding grounds of the Bering and Chukchi seas in October of every year and pass through the waters off Ventura, like clockwork, according to the boat’s captain, between Dec. 26 and April 4.

Island Packers also offer whale-watching packages for humpback and blue whales in July and August, but those trips are far longer (a full day) because the feeding grounds of those whales tend to be at the western end of the Channel Islands, some two to three hours from shore.

This day on the water may be a learning experience, but it’s far more visceral than it is academic. Once away from the coast and into the ocean proper, we slow to a puttering speed and watch for glimpses of grays — through zoom camera lenses, binoculars and naked eyes — surfacing for air.

Some 50 yards away, a series of spurts breaks the rolling calm of the water. Proof that these giant creatures are really here is a thrill. The whales surface for four or five puffs of air before they dive below to travel at greater speeds. As they dive, their tails, spotted with white like the rest of their long, smooth bodies, rise out of the water to wave farewell.

“They know we’re here, but we don’t want to be intrusive,” the captain says over the speaker. “Imagine you’re at home and 150 people burst into your living room. We want them to be comfortable with us.”

Laws designed to protect the whales from harm ensure that boats keep their distance and that they don’t travel over the top of migrating whales as they attempt to surface for air. When a nearby boater on a small sailboat floats directly over the top of a pair of grays, one of our boat’s crew members screams out into the sea. The boater denies that he has done anything wrong.

“One hundred and fifty people just saw you do it,” the crewman shouts. His passion is impressive. These whales are in good hands with this guy around. “If you do it again, I’ll call the Coast Guard.”

It isn’t long before spotting whales becomes a game among passengers. Everyone angles for better views as we share binoculars and vantage points. We’re awed by the size and quiet beauty of these unobtrusive animals, whose long bodies are visible a few seconds at a time. When it’s over, the three-and-a-half-hour tour — which included a quick, but beautiful, pit stop in the docking bay of Anacapa Island — feels like just a few minutes.

Until next year, our blubber-coated friends are off to warmer waters.

“Take a last look because we’re heading back,” the captain says. One last tail waves farewell and we head away from the wild blue yonder — and no one makes that dreaded trip to the back of the boat.