By Elizabeth Diffin
BBC News Magazine
Swimming with dolphins may be sold as a life-affirming experience, but research shows that it can be traumatic for the sea mammals themselves. So is it time to stop?
It regularly features as one of those transformative experiences to notch up on the "things to do before you die" bedpost - swim with dolphins and discover the very essence of life.
Many tour operators feature it in holiday packages. "You will feel completely free and at one with nature as you swim majestically along side these incredible creatures," is how one sells the experience.
Touching isn't recommended
But now doubt has been cast on health effects of dolphin swimming - not for humans, but the dolphins themselves.
British researchers have found that swimming close to bottlenose dolphins and trying to touch them can be highly stressful for the aquatic creatures - preventing them from resting, feeding or nurturing their young.
Lori Marino, a neuroscientist at Emory university in Atlanta, said they could suffer "psychological problems" stemming from swimming with tourists.
So should thrill-seekers looking for that ultimate life-changing experiences avoid this in future?
The Whale and Dolphin Conservation Society (WDCS) thinks so, primarily because it disturbs dolphins in their natural habitat. And since dolphins breathe air and so surface regularly, they can be followed by fast-moving vessels like water-skis and speedboats.
"People think if they make a disturbance, the animals will just move away," says spokesman Mark Simmonds. "But animals live in certain habitats. We might displace them, and they may not necessarily have a place that's equally good to go to."
The study focuses on tours off the coast of Zanzibar, Tanzania, where up to 30 boats will invade one pod and swimmers chase the dolphins in hopes of making physical contact. This can lead to the dolphins becoming unsettled - especially as the tours run throughout the day.
When dolphins feel sociable, they swim near boats
Newcastle University's Dr Per Berggren, who conducted the research, is equally concerned that if the dolphins leave - they can swim up to 50 miles a day - Zanzibar's tourism-driven economy will suffer.
"If this activity continues, it eventually will push them away. We haven't said to stop swimming with the dolphins. But you need to do this in a very careful way."
There are tour operators who try to interact with the sea creatures in a more responsible way, by limiting numbers of boats and passengers, and letting the dolphins take the lead.
In the open sea off the coast of Portugal, Amanda Stafford, of The Dolphin Connection, tells clients to wait for the dolphin to approach them - and keep their hands to themselves. If dolphins aren't feeling sociable, they make it obvious.
"Dolphins in the wild can go in so many directions," she says. "You have to be able to read their behaviour to see when they're interested in socialising."
But even this is too much, says Mr Simmonds, not least because of the risk of transmitting diseases between humans and dolphins.
"We like people going to see the animals," he says. "[But] the best thing is to watch the animals from land."
Dolphins like to travel in pods
And keeping dolphins captive at resorts or aquatic parks is akin to torture, says Dr Horace Dobbs, founder and honorary director of International Dolphin Watch, as it separates these sociable animals from their pods. "It would be like locking me in a lavatory. We should respect [dolphins] in the same way that we respect other people."
Humans do seem to feel a sense of kinship with dolphins, intelligent, playful, talkative creatures that they are. And separate research shows people feel the benefit from getting up close and personal with dolphins, says Dr Dobbs. This is because dolphins are thought by some, including Dr Dobbs, to emanate "chi" - the essential life force in Chinese medicine, and the basis of various therapies for clinical depression, autism and brain damage.
And Ms Stafford says her own studies in Australia show that when people interact with dolphins, their brainwaves show a more relaxed, dream-like state. It also stimulates the release of endorphins - known as the happy chemical - which induces feelings of joy.
So we may feel the benefit of swimming with dolphins - but the feeling may not be mutual.
"If a dolphin turns up, hordes of people turn up. They have an effect on the human psyche," says Dr Dobbs.