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Sea Life

Blog - Sea Life

The Physiology of Free Diving

The Physiology of Free DivingSeptember 21, 2009 - Constant weight free diving is a sport in which highly evolved land mammals, humans, swim deep underwater without supplemental air and return to the surface with the same weight they started with. In competitions tags are placed at various depths along a chain and the diver proves how deep he or she has gone by bringing back a tag. The men's record is held by Martin Stepanek who earlier this year swam down to and returned from 122 meters (400 feet) in 3:36 minutes with a single breath. Two women, Sara Campbell and Natlia Molchanova, have approached 100 meters (Molchanova set a world record by holding her breath underwater for 8 minutes). It's surprising that men and women can dive and return from these depths without anything more than a monofin, that no one has died in competitions and that there are no known long term effects (a few burst eardrums aside). But that's the case. Humans can dive to great depths because they posess the mammalian diving reflex. Alec Wilkinson explains in his August 24th New Yorker Article The Deepest Dive:

The mammalian diving reflex is activated when the nerves in the face come into contact with water, most effectively with cold water... First, the heartbeat slows; if you were to put your face into a sink of cold water for thirty seconds, your heart would slow too. Under pressures of depth, blood withdraws from the arms and legs and concentrates in the chest. This is called the blood shift. Meanwhile, the lungs compress, halving themselves after ten metres, then reducing by degrees until, by a hundred metres, they are something like the size of a fist; free diving is the only sport in which the lungs shrink and the heart slows. The blood shift prevents the chest from collapsing. In theory, however, a depth could be reached after which the chest became so compressed that the heart could no longer function... Shrunken lungs give a diver a sense of having plenty of oxygen... As a diver returns toward the surface, his lungs expand, more oxygen is consumed, and suddenly he feels as if he hasn't got enough to reach the surface. He might feel that he needs to breath, then suffer convulsions and black out... For someone holding his breath, the urge to breathe comes not from a lack of oxygen but from the accumulation of carbon dioxide in the blood as oxygen is used.

Here's a video of Martin Stepanek starting and returning from his record setting dive to 122 meters:

CWT RECORD 122M IN 3'36"! from Martin Štěpánek on Vimeo.

 
Blog - Sea Life

Cape Cod Sharks After the Media Circus

September 16, 2009 - The combination of great white sharks and a holiday weekend on Cape Cod were too much for the media to bear calmly. In headlines and blogs it seemed that the entire dialog of Jaws was represented online. Now that the story has faded the question that remains is this: was the actual number of great white sharks in the area greater than in years past or was this simply the first time so many have been seen?

This afternoon I had a brief conversation with Dr. Greg Skomal, the Massachusetts Division of Fisheries shark expert who has been closest to the subject. He said that there was no baseline for the number of great whites in Cape Cod waters so it's impossible to know if this year has been exceptional. "Maybe in five years we'll know," he said. He also said that the claim of 10-20 sharks in the area, the range reported by the media (and repeated by MoreBeach), did not come from him. There is no official count on the number of great whites swimming off Chatham.

Five sharks were tagged and fitted with small data recorders at the base of their dorsal fins. The recorders will track where they swim in the months to come. Some time this winter the recorders will pop off, float to the surface and transmit their data to Dr. Skomal and his colleagues. The information will then be shared with the public.

Blog - Sea Life

Growing danger: seal loves dogs and people



September 15, 2009 - On the Hawaiian island of Molokai a baby monk seal named KP2 has been a star. Since the animal arrived at Kaunakakai Wharf in February, several children from the island have made a habit of swimming with him. Area paddlers and boogie boarders have shared laughs watching him climb into or onto their boats and boards. One resident was so comfortable with KP2 that he put his golden retriever in the water with the seal and documented it in a YouTube video (above). KP2, an endangered Hawaiian Monk Seal, is so tame you can swim with him. But now he is likely to be sent away from his Molokai home. That's because the 17-month-old pup is maturing. His weight, now 175 pounds, has more than doubled since spring, and he has begun playfully grabbing swimmers from behind with his flippers. Here's the full story from Chris Herring at WSJ.com.

Blog - Sea Life

Another Cape Cod Manatee

September 14, 2009 - Another Manatee has found its way into Sesuit Harbor in Dennis. The manatee arrived on Saturday, having traveled the length of the east coast to get there, researchers say, stopping by Rhode Island last week during a journey from its home near Miami. Experts from the U.S. Fish and Wildlife Service were able to identify the 1,100-pound male from markings on its back and trace it to the Florida coast. They say the animal, which measures between 10 and 11 feet, was sighted off Rhode Island last week, leading them to conclude it would arrive in Cape Cod shortly after. Last year a manatee found its way into Sesuit Harbor in early October. Efforts were made to rescue the animal but were not successful. Here's the full story from WCVB Boston.

Blog - Sea Life

Three more great whites tagged



September 8, 2009 - A total of five great white sharks in Monomoy waters near Chatham have now been tagged with radio tracking devices, two over the weekend and three more this morning. One of the sharks is estimated to be 15 feet long, the others have ranged from 9' to 12'. Shark researchers are hailing this as a great opportunity to learn more details about the elusive great whites. Chatham's Atlantic adjacent beaches remain closed.

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