The elephant seal swam lazily above my companion, following him and matching his every move. I shot off a few pictures but was careful to hold back plenty of film. I knew this animal's predilection for taking unwary divers in a close embrace, and it made for great pictures. What do you do when an elephant seal wants to hug you? You let it!

The seal seemed bored. It yawned. Its teeth were the size of piano keys. I marvelled at the size of the gaping jaws, which seemed to fold so far outwards that they enveloped the animal's head. And then the seal dipped down and swallowed my buddy's head!

Yes, I'll say that again. The elephant seal swallowed my buddy's head!

To this day I cannot understand why I failed to press the shutter-release. It would have added only micro-seconds to what followed. I can only say that I am clearly not the opportunistic professional photographer I thought I was.

Instead, I attacked the elephant seal with my camera and strobe. It was like attacking a sofa with a Kleenex. I was amazed that the animal even noticed, but it gave me a sideways glance, released my buddy's head and, with what amounted to a disgruntled shrug, headed off into the green gloom to seek more co-operative divers.

Later, my buddy asked: "What happened down there? It suddenly went dark!"

"You don't want to know," I replied. It seems that the elephant seal had managed to encompass his head in its mouth without actually touching him.

Of course, not every elephant seal likes to play with divers. This was a solitary seal living in a busy colony of Californian sea-lions at Los Islotes, a guano-stained pile of rocks not far from La Paz. It probably got a better reception from divers than from the bull sea-lions aggressively guarding their harems.

The Gulf of California, or Sea of Cortez, is an almost land-locked stretch of water bounded on one side by the Mexican mainland and on the other by the long peninsula known as Baja or "Lower" California. On the map, it looks like the Red Sea.

It is a unique body of water because it is surrounded, like the Red Sea, by the fierce daytime heat of the desert, yet supplied with water from the cold currents that flow west of the American continent. Because of this, its water temperature fluctuates more throughout the year than probably those of any other sea.

The nutrients that thrive in its cold upwellings make this one of the most prolific seas in the world. Japan once tried to buy it from the Mexican government, because it was such a productive source of seafood!

Grey whales use it as a birthing ground in the winter months before heading with their calves north to the frigid waters of Alaska. Californian sea-lions and elephant seals make breeding colonies on its rocky islands. Hammerhead sharks school at such points as the submerged sea-mount of El Bajo. Tropical fish haunt its few coral reefs, and whale sharks and giant Pacific manta rays feed on its plankton.

The diving in the Sea of Cortez is unlike that anywhere else in the world because the conditions can vary so greatly from day to day. It's difficult to anticipate what you'll find, but go with an open mind and suits ranging from the lightest wetsuit to the warmest semi-dry, and you won't be disappointed.

Not to be confused with Bolivia's capital, La Paz is an inauspicious Mexican town at the southern reaches of the Baja Californian peninsula, and a good base for exploring the area.

The Cortez Club at La Paz is run by Jamie and Andre, who went to an English public school but have made their homes in Mexico. Visiting Brits will feel at home.

The Cortez Club runs fast pangas to the dive sites, and for those who like to start a dive burnt to a crisp, blasted by the wind and beaten to a pulp, there is an exceptionally fast RIB. It also runs a small liveaboard and dayboat to offer more stately progress for genteel clients who don't mind getting up early.

Either way, you have a good chance of running alongside pods of pilot whales as they surface, puff and blow, taking it in turns to keep a watchful eye on the people gazing from the boat.
I will always savour the image of a big bull sea-lion that looked like some munificent hairy uncle. It was floating alone in relaxed fashion in mid-ocean, gathering up hordes of squid in its hungry embrace. I swear it smiled at us as we passed by in the boat.

I went with Jamie and Andre to Seal Rocks. It's not a pretty place and has no seals, but there were plenty of female sea-lions and their gambolling pups to fill the water with non-stop theatre.

Swanne Reef is one of the few true coral reefs within an easy boat ride of La Paz. It teems with life to the extent that it affects the visibility. The occasional sea-lion hunting here is literally swimming in its dinner.

Visiting divers should not overlook the wreck of the Salvatierre either. This was a truck ferry that sank after it struck the reef back in the '60s. There isn't much left of it now - 30 years of storms in only 20m of water have seen to that. Only some elements of its superstructure, its twin propellers and the remnants of the trucks, including their tyres, are recognisable. However, it makes a good home for numerous pufferfish, porgies and sweetlips, and surgeonfish shoal in the open water nearby.

The warm water discharged by the local oil refinery at La Paz boosts plankton levels to the point at which the water becomes murky, but it's such a Mexican chowder of fish life that great Pacific mantas and whale sharks can suddenly appear out of the gloom, mouths agape for an easy meal. They are harmless to man, but still able to make a diver miss a heartbeat.

diving with elephant seals is a unique experience


whale-watching from the dive-boat


the wreck of the Salvatierre truck ferry


sea-lions at play at Los Islotes

GETTING THERE: La Paz has twice-daily flights from Los Angeles, which is well served with flights from the UK. At certain times there is a weekly charter flight from Gatwick direct to Cabo Sant Lucas, about three hours' drive from La Paz. DIVING: Cortez Club, 01273 731144, www.cortezclub.com; Baja Diving & Service, 01152 11221826, www.bajadivingservice.com. ACCOMMODATION: La Concha Beach Resort is a four-star facility attached to the Cortez Club. Club Cantamar Resort & Sports Lodge features Baja Diving. WHEN TO GO: Mid-September to mid-November is best. WATER TEMPERATURE: Big variation, from 20-30°C. MONEY: Mexican peso, US $, credit cards. DIVING SUITABLE FOR: A range of abilities. FOR NON DIVERS: Watersports, shopping, beaches, whale-watching at certain times of the year, and sea-lion-watching. COST: A 10-day package, including one night in LA, nine at La Concha Beach Resort, transfers, taxes and seven days' diving with the Cortez Club, costs from £650 per person sharing. A 14-night package costs from £850. Flights are not included and prices have been fluctuating, but a return to La Paz via LA starts from £350. FURTHER INFORMATION: Mexico Tourist Board, 0870 900 9866, e-mail: uk@visitmexico.com