Whales, manta rays and sharks roam near the islands of the Eastern Pacific

''Breathe! Stay calm. Don't swim at them or you'll drive them away. Move slowly and deliberately.''

Like a mantra, the commands pouring through my head hold me in check as a mother humpback whale, her calf and an adult male hover 60 feet below, placidly watching us.

Chancing one possible shot, I take a deep breath and silently slip 30 feet beneath the surface. Instead of fleeing, the mother and calf begin rising toward our small group.

The two cetaceans completely fill the frame of my underwater lens. Everything from the deep creases in their pleated throats to the giant follicles scattered across their heads and rostrums stands out with startling clarity Behind the whales is nothing but deep blue.

Few experiences can rival the electrifying sensation of sharing space with some of the ocean's largest creatures. For divers seeking these types of unforgettable encounters, the Eastern Pacific's family of volcanic islands: the Islas Revillagigedo, Cocos, Malpelo and the Galapagos are the place to go.

It's not unusual to come across humpback whales in the Islas Revillagigedo, which sit 220 miles south of Mexico's Baja Peninsula. Part of the same North Pacific group that migrates to the Hawaiian Islands, the whales return to these isolated islands annually from mid-January to early spring for age-old mating rituals. During their stay, the ocean is filled with whale songs and thunderous breaching.

Getting more than a glimpse of these majestic leviathans underwater, however, is a rare privilege.

''Be appreciative of the little gifts the ocean gives us'' urged Axle, our divemaster on the Solmar V live-aboard.

Fortunately, the divers on this voyage had enjoyed many gifts, including hospitable manta rays and a diverse collection of sharks.

GIANT MANTAS A manta ray is the largest member of the ocean's family of rays. According to the textbooks, the manta's average wingspan is between 8 and 12 feet. The manta rays for which the Islas Revillagigedo are best known are anything but average. Their typical wingspan is at least 15 feet, and some of the bigger ones measure 18 to 22 feet.

Size aside, the extraordinary behavior of seeking harmonious interaction with divers is what sets these delta-winged behemoths apart.

The rays typically initiate engagements, positioning themselves a few feet overhead so divers can easily caress their bellies with bare hands (the use of gloves is forbidden under Mexican law).

Unlike the soft, velvety underbelly of a stingray or skate, mantas have skin as coarse as sandpaper. Get carried away on the tummy rubs and your experience will include a souvenir; abraded skin across the fingertips and palms, a condition known as ''manta hands.''

The manta encounters occur most frequently near San Benedicto Island, the second largest in the Islas Revillagigedo. Anywhere from three to a dozen mantas will show up, vying for attention. During several dives on prior visits the mantas actually out-numbered divers by a 2-to-1 ratio. Some of the mantas have been known to stick around for an entire day and then return again for more the next morning.

HAMMERHEAD TRIANGLE Due to their widely publicized aggregations of scalloped hammerheads, the islands of Cocos, Malpelo and the Galapagos archipelago collectively form what shark enthusiasts call the ''Hammerhead Triangle.''

Like the Islas Revillagigedo 1,400 miles to the northwest, the towering volcanic formations of these three islands are as striking as they are imposing. The mountainous landscapes of Wolf and Darwin Islands in the northern Galapagos and Malpelo are largely desolate, with little in the way of vegetation or fresh water. Cocos, on the other hand, is blanketed by a lush rainforest and waterfalls.

Underwater, these islands are virtually indistinguishable. The subsea terrain bounds off into the depths over mounds of barnacle-encrusted boulders, pounded ridges and pinnacles made of igneous-based rock. Due to the region's temperate nature, there is only a limited presence of stony corals, gorgonians and black coral sporting yellow, pink and even fluorescent green hues.

Vast schools of fish rule the biosphere of the Eastern Pacific. Nearly half o the species are endemic to the region, ranging from the Islas Revillagigedo's vivid orange clarion angelfish to the Galapagos' equally gaudy blue-banded goby. The marine life also includes guests like moorish idols and longnosed hawkfish that are usually found far away in the Indo-Pacific and Red Sea.

But for divers, the thriving array of sharks is the big-ticket attraction.

My recent visits to Darwin and Wolf Islands in northern Galapagos resulted in encounters with huge numbers of hammerheads, Galapagos and silky sharks. But the opportunities to come face to face with some of the biggest whale shark that I've ever seen were the real highlight. Nothing puts the thrill meter in overdrive like seeing a fish as big as a city bus casually cruise by.

The same can be said about Melpelo and Cocos, where I enjoyed repeated rendezvous with whale sharks, hammerheads and even a large and inquisitive Pacific sailfish. Melpelo is loaded with moray eels which Cocos has so many whitetip sharks, marble rays and sea turtles that it's sometimes hard to avoid them.

THE SHOW IS NOT OVER UNTIL... Hundreds of miles from the continental shelf, these islands act as way stations for just about everything that swims the open sea. Although sharks and rays could easily be viewed as signature features of the Eastern Pacific Islands, their marine communities also include large wahoo, tuna and marlin, plus a sizeable assortment of dolphins and whales.

Countless times, I have watched schools of bigeye jacks so enormous that divers would actually vanish in the middle of their swirling nexus. Others divers have returned to the boat with stories about being visited by pods of bottle-nosed dolphins during their safety stop, proving that no dive is over until you leave the water. During my last trip back from Cocos, our vessel passed a pod of sperm whales lolling on the surface; sometimes the show's not over until you're back in port.

Obviously, not every dive is filled with nonstop action. There have been rare instances here when I've felt fortunate to find a shark or sea turtle.

It's important to understand that all these creatures play by their own rules. When venturing below the islands of the Eastern Pacific, keep a watchful eye and a patient spirit.

When the show starts, the stars are likely to blow your mind.

A WHOLE OTHER WORLDDiving in the Eastern Pacific is an acquired taste. Unlike the typical Caribbean venue, sea conditions in the Eastern Pacific can turn rough with large swells and chop. Below the surface, expect strong currents, surge and water temperatures in the 60s to low 70s.

Water clarity can vary sharply, ranging from 100 feet to murky conditions reminiscent of your last quarry dive. A large supply of food, namely plankton and small fish, is needed to support such an ample population of ocean predators. Hence, the higher the abundance of plankton, the lower the visibility.

The islands lack airstrips and hotels. Long-range live-aboard vessels are the only viable means of exploration. In all cases, this entails a long, sometimes arduous sea crossing. The award for the longest goes to Cocos, with an average crossing time of 36 hours between Puntarenas, Costa Rica, and the island. Once you arrive, most of the diving in this region is conducted from large, outboard-powered inflatables or skiffs.

WHEN & WHERE Finding the Eastern Pacific's ''Big Stuff''

Sea Lions: - Central and southern Galapagos Islands; all year. - Islas Revillagigedo (Sea of Cortez) has the largest reproductive Sea Lion colony with over 100 Sea Lions. The waters are the warmest and visibility is best from July to October. During this time, the Sea Lion Pups are very playful with divers. Click Here for trip detials!!!!

Manta Rays: - Best bet is Islas Revillagigedo; November through May/June. - 2nd choice is Cocos Island; year round. - 3rd choice is Galapagos Islands; December through March.

Dolphins: - Found near all of the islands, but close encounters are a matter of chance; year round.

Humpback Whales: - Best bet is Islas Revillagigedo; lat January through late April.

False Killer Whales and Pilot Whales: - Best bet is Malpelo and Cocos Islands, though encounters are rare; year round.

Green Sea Turtles: - Best bets are Galapagos Islands, Cocos Island and Malpelo Island; all year.

Hammerhead Sharks: - Best bet is Galapagos Islands; June through October. - 2nd choice is Cocos and Malpelo; July through November. - 3rd choice is Islas Revillagigedo; November through June.

Whale Sharks: - Best bet is Glapagos' Darwin & Wolf Islands; June through October. - 2nd choice is Malpelo; June through October. - 3rd choice is Cocos Island; all year.