On a sledge into the deep blue sea

By DANIEL JACKSON

Tanya Streeter slows her heart rate from 48 beats a minute to 12.

She then fills her lungs with almost twice the amount of air a normal person is able to take in and descends at speed into the ocean to depths only scuba divers usually reach.

The 28-year-old American freediver descended to 91m in chilly seas off the Poor Knights Islands yesterday.

Over the past week she has been attempting a dive of 100m using a weighted sledge to take her down and a balloon to bring her back up.

The assisted dives are in a category of freediving known as "no limits."

"It was pretty cold all right, but beautiful underneath. It always is," she said yesterday.

Most humans would only ever venture to such depths in diving bells or with special scuba equipment and using mixed gases, as oxygen is toxic at that pressure.

Mrs Streeter is the world record holder in several categories of freediving, which involves participants diving as deep as they can on only one breath.

She and her husband, Paul, flew from their home in Texas to take part in a documentary about the sport being filmed in the waters off Tutukaka.

Scuba divers, who filmed the Second World War wreck of the Niagara near Tutukaka as part of the documentary, had problems when their camera bulbs were crushed under the pressure of the depths she has been reaching.

Mrs Streeter, who has a best depth of 113m, held the women's world record in the "no limits" category for two years until another competitor reached 130m.

Until yesterday, her efforts for the documentary were hampered by poor weather and choppy seas.

Mrs Streeter estimated that at a depth of 91m, the the pressure was about 1034 kilopascals (150 lb per sq in).

She said she liked the challenge of the sport. "It's not death-defying, it's life-affirming."

The main risk in freediving was losing consciousness on the descent.

"If you are in a situation where you black out underwater, it is unlikely you will recover on your own."



Before diving, she performs breathing exercises similar to yoga and stretches her ribcage, which allows her to use the full capacity of her lungs.

The exercises also slow her heartbeat so she uses less oxygen.

"Most women's lungs can hold about 3.5 litres of air. Mine can hold just over six litres."

Her body also goes through a process known as the mammalian dive reflex, which is similar to what happens to seals when they dive.

As she descends and the pressure around her body increases, blood from her extremities moves into her lungs, organs and brain.

After about 40m her lungs actually become solid, as the air inside them compresses and the fluids in her body equalise with the pressure of the water that surrounds her.



"You have to go through a real learning process about yourself. There is a journey you have to go through to decide you are going to do it. After that the records become irrelevant."

Irrelevant or not, Mrs Streeter has stacked up an impressive six world records, four of which she still holds.

She started in the sport only three and a half years ago after a friend noticed that she had a natural talent for it.

After completing the filming in Northland, she will take a workshop on freediving in Auckland.

On the journey home she will stop in Hawaii, where she will compete in the United States freediving championships.

The film of her dives is for a documentary being co-produced by National Geographic International and the Dunedin-based film company Natural History New Zealand.

The documentary is part of a series of six, called The Force, which will feature extreme sports and the people who do them.

The series may screen in New Zealand in about 18 months.