Sleeping shark question?????

[Wildcard]

Which sharks "sleep"? That is which HAVE to keep moving? I know it used to be common thought that sharks couldn't stop moving and rest. I have seen otherwise and would like to know what is known now. Thanks.

 

[scottfiji]

Bottom dwelling sharks such as horn sharks, swell sharks, cat sharks, zebra, wobbegongs, angel sharks, and others can rest on the ground for a while (a while meaning most of the time). They have the ability to pump water over their gills using a gill pump, this is called buccal pumping. Other sharks (tiger, white, blue, bull, etc.) must keep moving with an open mouth, called ram ventilation. Some sharks, like lemonnurse sharks, can switch between both. But lemon and nurse sharks have to work very hard to pump water when resting, so they're not really resting.

Some sharks that utilize ram ventilation have been found sleeping in caves. The water in these caves seems to have a higher oxygen content from freshwater seeping in.

Others such as archman can probably expand more on this topic.

Scott

 

[sapphire]

Thanks for the explanation, Scott. I have been wondering about this ever since I visited Cabo and was shown where the White Tipped Reef sharks hang out in a cave. If they are supposed to be the "keep moving" kind, how are they able to stay still in a cave like this??

Jennifer

 

[scottfiji]

Thanks for the explanation, Scott. I have been wondering about this ever since I visited Cabo and was shown where the White Tipped Reef sharks hang out in a cave. If they are supposed to be the "keep moving" kind, how are they able to stay still in a cave like this??

Jennifer

I think this is still sort of a mystery. Scientist are actively studying sharks sleeping in caves. From what I've read, some of these sharks, like Tiger Sharks, have spiracles (small gill slits behind the eyes) that provide oxygen. These spiracles are probably used to provide oxygen to the brain. It helps that the water in the caves have extra-oxygen from underground springs.

By the way, I don't think any shark actually "sleeps" like a person does. They might be resting, but their brain doesn't completely shut down as much as ours does. The question regarding whether sharks have an analogy to our sleep is being studied now. Sharks that look like they are sleeping have much more of an awareness of their surroundings than we do when we are sleeping.

 

[archman]

Others such as archman can probably expand more on this topic.

Nope. You did a pretty good job. Many ichthyologists couldn't do better, without looking it up.

So I looked it up. Your bottom dwellers and "dual" forms maintain nicer spiracles than their pelagic cousins. Spiracles serve as an alternate water intake when the animal is sitting on the bottom or at rest. Muscles around the gills create the pumping action.

You can locate the spiracle by looking directly behind the eye, before you get to the first gill slit. It looks like a hole.

A lot of open water sharks either don't use their spiracles anymore, or it's gone altogether.

Hmmm... I'm not sure how accurate this factoid is:

For the shark species that do make use of it, it only supplies oxygen to the brain and eyeballs (via blood vessel separate from main respiratory system).

That doesn't sound right for critters like wobbegongs and nurse sharks. I'd of thought they'd be more like this:

Spiracles are better developed in skates and rays, and actively pump water across the gills directly.

 

[Wildcard]

Good stuff. Thanks guys.