Marshalled by our guide, the six of us flipper-kicked cautiously towards the craggy shore of North Seymour, in the central Galapagos Islands. Soon the younger sea lions spotted us walking towards the craggy shore, began to waddle excitedly down the rocks and plopped into the sea. Half an hour later, my usually cynical friend Charlie surfaced after a couple of underwater somersaults in unison with two sea lion pups, and nicely summed up swimming with sea lions: “This,” he said, “is the best thing I’ve ever done.”

On this, our first encounter with sea lions, there were 12 or so chubby little pinnipeds (pinniped is the group name for seals, sea lions and walruses) in the water with us. Initially, they had bundled into a tumbling sub-surface maul about 10ft away, trying to peer at us and hide behind each other at the same time. Suddenly, one shot at us, spun at the last second and rocketed underneath us.

Then they were all around us, and they wanted to play. They dived down when we dived down, copying every twist, turn and roll. They zipped, zoomed and leapt about our overjoyed little group. They swam next to us, fascinated eyes staring straight into ours, then flicked their tails and shot off like jet-powered aqua-labradors after a stick. If we stayed still, then spun around, we’d always find two or three sea lions, heads out of the water, creeping up behind us, Grandmother’s Footsteps style. Caught, they’d scatter at extraordinary speed, then screech round and play the dart-up-and-miss game again.

We encountered these charming animals during a sailing holiday around the Galapagos. Much as we appreciated the richness of the wildlife there – the blue-footed boobies, iguanas and albatrosses – we all fell for the sea lions like preteen girls fall for ponies. That night, as sea lions chased flying fish around the boat in the company of turtles and schools of golden rays, we wondered why swimming with dolphins always topped the “things to do before you die” lists.

How could dolphins, we asked, be half as much fun as sea lions? Or a quarter as cute? None of us had swum with dolphins though. I had tried once in Greece, but the dolphins had swum away.

So, back home, I contacted Tanya Streeter, the world champion free-diver, television presenter and expert on interacting with marine life. She has swum with more dolphins and sea lions than you can shake a snorkel at. I asked her which was better.

“First thing,” Tanya explained, “is that you must only swim with animals in the wild. Keeping any animal in captivity to swim with humans is cruel. Given that, dolphins are much more difficult to swim with because they’re not that interested in humans.

“People have a distorted view of dolphins. When they swim at you with their mouths open, people think they are smiling. Actually they’re saying, ‘Get out of my way, or I’m going to bite you, and these are the teeth I’m going to do it with’.

“I have had wonderful encounters with dolphins, but they’re much less curious and playful than sea lions, and you’re always aware that they’re big, aggressive animals.

“To keep dolphins interested you have to dive deep and swim fast, which most people can’t do. Sea lions, though, are like boisterous puppies. They’ll shy away at first, but they can’t resist the temptation to check you out. They just seem to be going at it the whole time – pulling each other’s fins, blowing at each other – and they’ll involve you if you’re in the water. They’ll even bring you presents: an adolescent sea lion once brought me a beautiful blue starfish.

“On balance,” concludes Streeter, “I’d rather be with sea lions any time.”

Pinnipeds can be found in North and South America, Africa, Australia and Great Britain. In the UK we have grey seals and common seals. Seals differ from sea lions by having no ear-flaps, and, with fins that are not so well adapted for land, they are even more inept ashore.

According to Clive Pearson, who runs seal swimming trips to Lundy Island, British seals are just as inquisitive as their Galapagan cousins, if a little less manic. He also advises some caution: grey seals are Britain’s largest carnivore, after all.

So can these animals be dangerous? In the Galapagos Islands, we felt completely safe. From previous research, I knew of only one pinniped who had attacked a human; an Antarctic leopard seal killed a researcher in 2003. But we were miles from the Antarctic. Moreover, our guide hadn’t been bitten in ten years. She said it was OK to swim and got in the water too, which was enough for us.

So, with the caveat that you must always go with someone who knows what they’re doing, take a plunge with a pinniped and leave the dolphins to the masses. Swimming with seals or sea lions is undoubtedly the most fun you can have with a wild animal.

Tanya Streeter appears in Wild Tribe: Reef Gypsies, tomorrow on BBC2 at 5.40pm

Need to know

Angus Watson flew to Guayaquil, Ecuador, with Trailfinders (0845 058 5858, www.trailfinders.com) from £695 return. Flights from Guayaquil to Baltra (Galapagos) can be booked from the UK for about £200 with local airline Tame (www.tame.com.ec), but must be paid for in person in Ecuador. Original Travel (020-7978 7333, www.originaltravel.co.uk) offers Galapagos tours, with all flights, from £2,700.
Angus Watson’s guide was Patricia Stucki (pat_stucki@hotmail.com).

More seal spotting

Australia: Kangaroo Island, near Adelaide, has seals and sea lions. Trips are run by local operators.
South Africa: Hout Bay, near Cape Town, has a playful colony of cape fur seals, says Francois Hugo of Seal Alert (www.sealalert.org). Dive trips can be arranged with Pisces Divers (00 27 2 1782 7205, www.piscesdivers.co.za).
Mexico: Swim with sea lions in the Sea of Cortez, Baja California. Trips are run by local operators.
UK: Clive Pearson’s Clovelly Charters in Devon runs swimming and diving with seals trips to Lundy Island (07774 190359, www.clovelly-charters.ukf.net).
See seals in Britain without getting wet: National Seal Sanctuaries: (01326 221361, www.sealsanctuary.co.uk ).

Tanya Streeter’s top tips

Never swim with captive marine animals. They are in a grotesquely inhumane situation.
The fitter you are, the longer you can play and stay underwater.
Don’t swim where there are huge predators that might mistake you for a sea lion.
Let sea lions come to you. If you appear threatening, animals will flee or become aggressive.
Never reach out and touch any wild animal. Keep aware of what’s happening around you.
Ensure that you are accompanied by someone who understands sea lion behaviour.

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