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PostPosted: Wed Mar 10, 2010 1:12 am
  

Senior ArloNetizen

Joined: Jul 30, 2008
Posts: 374
Location: Washington, DC
Captain Zap wrote:
I believe that some sharks need to keep moving or else the suffocate. The aforementioned have no way of forcing water through their gills if they are not moving. They don't really sleep, either. More like going into standby mode. What a pisser, huh? Sleepin's one of my favorite things. Guess I wasn't a shark in a past life.


I think it makes it more, not less, likely you were a shark in your past life -- you're trying to catch up now.

I used to think sharks had to always move or suffocate (I learned that from Woody Allen), but then some friends scuba diving saw the cave sharks discussed in this geeky discussion of sharks, so you're right, it's just some that need to move:

http://www.elasmo-research.org/educatio ... _sleep.htm

Quoting from it:

But when it comes to whether or not sharks sleep, we just don't know. There have been reports from all over the globe, including Mexico, Japan, and Australia, of sharks resting motionless in caves. These have been called "sleeping sharks", but I can attest that the eyes of these quiescent sharks do follow divers moving about in the caves with them, so they're definitely not asleep.

In his sweeping epic Paradise Lost, 17th Century English poet, John Milton, asked, "What hath night to do with sleep?" We know from sonic telemetry studies (the underwater equivalent of radio tracking) that at least some shark species — such as the Reef Whitetip (Triaenodon obesus) and the Tiger Shark (Galeocerdo cuvier) — are actually more active at night than during the day. Since schooling behavior is partially coordinated by vision, many other sharks are most active at dawn and dusk, when such prey is at a disadvantage. Studies such as these suggest that at least some sharks do not sleep at night.

We used to think that the Great White Shark (Carcharodon carcharias) was primarily active during the day. But it turns out that this is largely due to observer bias: humans tend to be diurnal rather than nocturnal, and it's very difficult to watch an underwater creature at night. Recent experiments by Peter Klimley using stationary telemetry pods placed along the bottom at the Farallon Islands, we have learned that White Sharks are quite active at night, when they probably feed primarily on bottom fishes. If these bottom fishes are sleeping when attacked, they're certainly in for a 'rude awakening'!

Because sharks rely on ram-ventilation — that is, their forward swimming to push oxygen-bearing water through their mouths and over their gills — this fact begs the question: do sharks sleep at all? Dolphins are conscious breathers, actually having to think about rising to the surface, opening their blowholes, and breathing. From Russian studies carried out in the early 1970's, we know that dolphins catnap in 2 to 3-minute stretches, actually shutting down one hemisphere of their brain at a time. From experiments carried out on a small shark called the Spiny Dogfish (Squalus acanthias), we know that the 'Central Pattern Generator' that co-ordinates swimming movements in sharks is not located in the brain, but in the spinal chord. Thus, it is possible for an unconscious shark to swim.

There is even a possibility that the sharks' fore, mid-, and hind- brain shut down in sequence, resulting in the shark equivalent of sleep-walking.

++++++

Back to me: sleepwalking sharks; what a concept. Not sure I agree with the writer that eye movement indicates no sleep -- if they can sleep-swim, I wonder if they can sleep-watch. I guess we'll never know...


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PostPosted: Wed Mar 10, 2010 12:07 pm
  

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Arlo Fanatic

Joined: Sep 12, 2000
Posts: 6517
Location: New Jersey
Nocturnal sharks? This may explain why bars are filled with lawyers after dark.


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PostPosted: Fri Mar 19, 2010 11:31 pm
  

I heard him talk on a local radio program about the whole thing. He said (and I loosely quote) "I felt that it was in conflict with separation of church and state." He said that was the primary reason as he felt making any religious oriented symbol was inappropriate in public school shop class. The implication being he would not allow any religious icon to be fabricated in his shop class. The way it was reported in the Des Moines Register was a bit distorted according to the teacher himself. I assume other reports were equally distorted. didn't read the link provided.


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PostPosted: Sat Mar 20, 2010 12:31 am
  

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Arlo Fanatic

Joined: Nov 11, 2004
Posts: 2010
Location: Left-of-center
The Des Moines Register quoted the teacher.

"Personally, I think it is offensive to worship rocks and trees," he told The Des Moines Register. "I am just trying to be moral. I don’t know how we can profess to be Christians and let this go on."

Sounds pretty prejudicial and self-righteous to me. But what do I know? I'd be more inclined to believe in the rocks and trees rather than a pie-in-the-sky, bearded dude who nobody can actually verify ever seeing.


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PostPosted: Sat Mar 20, 2010 8:13 am
  

Arlo Fanatic

Joined: Sep 15, 2001
Posts: 3682
Location: Dallas, Texas
Captain Zap wrote:
Sounds pretty prejudicial and self-righteous to me. But what do I know? I'd be more inclined to believe in the rocks and trees rather than a pie-in-the-sky, bearded dude who nobody can actually verify ever seeing.

Yup. (If this were Facebook, I'd have hit the "Like" button.)


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