Why do sharks can't stop swimming?
114432
Ok, I know that the bit about sharks not breathing if they're still is still taught at school, and essentially it has some point. It's true that gill oxygenation is better when the water flow through the branchial area is greater. \nBut sharks DO indeed stop swimming, they can rest near the bottom of the ocean (as if sleeping) and they use the pumping motion of the floor of their mouth (their mostly immobile tongue) to help water move through the gills. \nBut as I've said, immobile sharks lie mostly near the ocean floor. This is because they're rather dense with respect to water (they don't have swimming bladders like bony fishes do), although their enormous, fat-filled liver increases their buoyancy significantly (along with other physiological characteristics). When they swim, sharks can keep themselves in midwater; the movements of the trunk and tail generate the necessary thrust to keep them from falling to the bottom.
358470
Dolphin's don't 'sleep' in the sense that we do. They do however have conscious control over their breathing like we do, in which case loosing consciousness in the ocean could be quite deadly. Research into this area suggests dolphins 'sleep' one cerebral hemisphere at a time, meaning they close down one half of their brain for a little while, letting the other half take care of the necessary functions such as breathing.
1043557
Relax, don't make any agitated movements, try and float horizontally.\n\nthe shark is attracted to movements and hence will go away if you do not thrash about.\n\nAlso, as its jaws are below its body, floatong flat makes it ver difficult for it to attack if uou are on the surface.
89291
I just saw on the Discovery Channel that they have created a shark repellant.  This is a device that omits a frequency that the shark dislikes.  A scubba diver attached this to his tank and then the swimmer pushed a button that released the frequency...I guess sharks do most stuff because of vibrations and frequency in the water...it's kinda like their eyes.\n\nAnyways, scientists are hoping to develope this further so they can get rid of nets along the coast <which kill sharks, dolphins, and turtles>.
1123272
Q: Can fish change their buoyancy? If so, how?\n\nA: Yes, many species of fish can change their buoyancy. There are four different strategies that fish use:\n\n1) incorporation of large quantities of low-density compounds in the body (i.e. oils and fats)\n2) generation of lift by appropriately shaped and angled fins and body surfaces during forward movement\n3) reduction of heavy tissues such as bone and muscle\n4) use of a swimbladder as a low density, gas filled space\n\nMany species of sharks use oils to regulate their buoyancy. The hydrocarbon squalene is a low density oil that is found in sharks and is believed to function in buoyancy control.\n\nSwimbladders allow for precise control of the fish's depth because the volume of gas they contain can be regulated quite easily. The idea behind the swimbladder is relatively simple. Air is less dense than water, therefore, air floats on top of water. In the same way, if you think of an oil spill, the oil floats on top of the water because oil is less dense. The swimbladder of the fish holds air, which allows the fish to be lighter in the water and making it more buoyant. If the fish lets air out of the swim bladder it will get more dense and begin sinking.
1015944
well the water is wet so take a towel.then the water is deep so you need to swim...then their are animals in the water and they poop in the water so yuoll get poop on ya and thats if they dont eat ya...the sharks that is
1132296
I'm not, but it's ok. Many people get scared of the water. Overcome the fear and you'll get over it. Even if the beach had a chance of sharks, they live farrrrr into the ocean. Just make sure you have nothing shining on and no blood dripping at on your skin and you'll be ok. (I went into oceans where sharks live there. No accidents. :) )
210284
fish are cold-blooded and cannot regulate their body temperature.  their body temperature will be within a few degrees of the ambient water temperature.  only mammals (dolphins, whales, etc) can self-regulate temperature.
1109553
I don't know why, but USUALLY it slows enough while you are in water that it virtually stops. However, it doesn't always stop (trust me, been there). Your best bet if you are going swimming is to use a tampon. Better safe than sorry.
411135
I think, and my marine physiology is rather out of date, that if a swim bladder was so packed with air that it would be unable to hold any more, the fish would be forced to the surface because of increased buoyancy, unless it expended a huge amount of energy to counter that (think 'swim down' from Finding Nemo, but have them doing it all the time).  If the swim bladder was unable to take in any air at all, and was somehow kept empty, the perch would sink unless it made the effort to keep itself at a certain depth.
271806
dolphins sleep by "turning off" half their brain at a time. They can't sleep as we do because for them breathing is not an autonomic impulse. In other words, they breathe like we move our arms, they need to decide to breathe, then get their muscles to carry out the orders. So a dolphin will shut off half their brain at a time. While one half gets some r & r, the other half makes sure the dolphin keeps surfacing at regular intervals to breathe.
631008
Sharks are boneless fish, so very primitive evolutionarily-they harken back a few hundred million years, without very much change- I seriously doubt, both because they are so primitive and havent changed in so long, that they have any remaining vestigial structures.  Generally vestigial structures come from an animal that has evolved from a quite different precursor-sharks are very close to the very first fish that evolved, thus they probably havent had to shed any organs or bones that arent useful.\nRibs? How is that vestigial?  They use their ribs for structural support, just like all fish...
48552
Fish are designed to swim. The obvious answer however is because they have fins and a strong tail that propels them through the water.
432907
Is there a reason you're asking this question under a new name?  Did you not like the previous answers?\n\nMy answer from: \n\nhttp://answers.yahoo.com/question/index;_ylt=Aosgux8O5O_.4Y0ThAeGgyjsy6IX?qid=1006041806251\n\nSome sharks are very slow and the average person can easily outswim them, at least for the short term. Sharks probably have better stamina and would eventually catch up.\n\nRemember, sharks are a very diverse group. There are huge, filter-feeding whale sharks and tiny little miniature dogfish. Everything from the weird cookie-cutter sharks to the weirder goblin shark.\n\nGuitarfish are especially slow sharks, if I remember correctly.\n\nYour real question is, Will someone ever be born who can outswim the *fastest* shark. The answer is probably no. We are not well designed for life in the water and our swimming is extremely clumsy. Evolution has no reason to fix any of these problems given we are resolutely terrestrial.
112066
Sharks in general are poikilotherms or ectotherms (their body temperature is similar to the temperature of the surrounding water). \nHowever, some species (high-power fast swimmers belonging to family Lamnidae, such as genus Alopias -thresher sharks- and Lamna - porbeagle and others- ) have partial endothermy. That is, they're able to "hoard" the heat generated by muscle activity and therefore achieve differential temperature zones in their bodies, which are some degrees above water temperature. This is achieved by means of special countercurrent blood vessels and rete mirabilia. \nSome typical body parts that are kept warmer are the brain and eyes, the swimming muscles, and the "core" with the visceral organs, which is logical given that higher temperature allows a higher metabolic rate of these important organs.\n\n---------------------\nAmy: not only sharks, also tuna and related bony fishes are endotherms. And some reptiles too.\n------------------\nNew update: Wow, this question keeps getting answers that state that only  birds and mammals are endotherms. Please, people, if this is what they taught you at school, try to investigate a little further. Of course MOST sharks are "cold-blooded" (that is not the happiest term, it's better to say ectotherm - meaning that it gets its body heat from outside - or poikilotherm - meaning that body temperature is variable). But endothermy is an advantageous trait, and it has evolved independently in many animal groups.
439262
I don't know anything about a "Sonic Shark Repellent". \n\nHowever, when you are diving in the Keys you should pay special attention to "current" and "wildlife".\n\nOcean currents can behave erratically when you are diving, especially around certain reefs. Just keep your "bearings" straight and you will be fine.\n\nDO NOT "handle" the wildlife. At some reef's the fish and "wildlife" will be quite "friendly". BE CAREFUL! Unless your qualified diving partner says its "OK" use the "LOOK BUT DON'T TOUCH" principle.( I don't want you to lose a hand or finger.)\n\nDO NOT touch the reef it-self. It is "un-cool"( and even illegal on some reef's), to "take a souvenir". Be happy with the experience of "the dive". Years ago my brother made the wrong decision to take some "cool looking red coral" as a souvenir. He wasn't wearing gloves. His hands swelled up like a balloon. Apparently, it was "Fire Coral",( that's what our guide told us later). \n\nJust make sure ,when you are in the water, to be aware of your surroundings; don't wear "flashy" watches or jewelry, and LISTEN TO YOUR GUIDE. \n\nObviously, you will want to wear appropriate "gear". And you should ALWAYS wear "booties" or "wet-shoes" when swimming,(coral can "eat" your feet up! Besides, you don't want to "kick-up" a Ray!) \n\nYou are going to have a blast! WISH I was going! Good Luck!
551194
1st off the sharks are always there you may not see them but they are there I have been surfing manytimes and had a shark swim right by me fishing with live bait is not going to attract sharks un less its bigger and a very bloody bait they are attracted to large fish and bloody meat not little shrimp and shinners which is what wade fisherman use along with shrimp and such you are more likely to get worried if someone is using chicken to catch crabs then anything and then you are looking at a thigh not a whole chicken the blood could attract them but not likely I have doen it many times and not a single shark bite on my line