Why cant sharks swim backwards?
466827
Because they were created without the reverse gear!
194730
I think it has something to do with the fact that the fish are not grounded to the earth so the current just travels around them not through them.
504128
Sharks do have backbones, as all vertebrates. Sharks do not have true bone, but their cartilaginous skeleton can be heavily calcified so that their vertebrae have the apperance of "bone" because they look like hard white cylindric spools. You might have seen their vertebrae made into necklaces and such by artisans. \nThis is what a shark trunk vertebra looks like:\nhttp://www.marinebiodiversity.ca/shark/english/porbeagle_vertebra__copy.jpg\nAnd without the neural and haemal arches they look like this: \nhttp://homepage.mac.com/mollet/Cm/BaskingSharkImages/basking%20shark%20vertebra%204.jpg\n\nAnd these are fragments of backbones:\nhttp://www.indonetwork.info/member/77806_backbone2.jpg\n\n(Notice the white color because the cartilage is calcified.)\n\nAlmost all the cartilaginous fish have backbones made of vertebrae (i.e. both sharks and skates/rays); the exception are the chimaeras or ratfish which do not have vertebrae, but retain a notochord (the primitive condition).
347164
YES! but that would depend on what species.\n\nsurprising to some, but NOT all sharks die when they stop moving. infact some species even tend to lie motionless at the bottom of underwater caves.\n\nCaribbean Reef Shark (Carcharhinus perezi)\nBanded Houndsharks (Triakis scyllium)\nWhitetip Reef Shark (Triaenodon obesus)\nLemon Sharks\nGrey Reef (Carcharhinus amblyrhynchos)\nBlackfin Reef (Carcharhinus melanopterus)\n\nare just a few examples.\n\nangel sharks lie motionless covered with sand on ocean floor to ambush prey.\nwhile some sharks "sleep"\n\nhope that helps :)
79520
Yes it is you have to do laps and make sure your doing them right. I'm a diver and I do laps all the time backward,sidewards,frontwards,and underneath are the best. Also if your not afraid of the diving board do a few jumpslike frontwards,backwards,fronttucks,and backtucks those are the simple ones. Hope this advise works.
35913
Well, generaly, a large fish is bound to only swim in the ocean because there is enough space for it. Also it depends if the fish lives in salt water versus fresh water.
129124
the basic of swimming is that u must breath in i.e fill ur stomach with air then streach ur legs nd hands nd start flapping them like a bird(only legs) nd as far as ur hands r concerned move them in the backward direcion like dis(ur hands->,<)\n\n 1 <(position of ur hands in the forward direction)   then             2 >(backward direction)
254827
Their legs have been modified into flippers so they would be unable to move an land.  Also their pelvic and pectoral girdles would not be able to support their weight with out the help of the water.
962319
Animals evolve to suit their habitats. Monkeys have tails that allow them to grip whilst brachiating through trees.\nMy point is, if an animal is to be born in a place with water then technically it should evolve to be able to swim. If an animal such as a desert creature was to be evolved then it wouldnt need to be able to swim. So no, not all animals can swim because they dont need to so they didnt need to be created that way.\n\nHope that helps!
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...
609755
It's a good question, and one that is still not fully answered.  When we speak of "instinct," as some of the other answerers did, we actually asign the problem to a black box and leave it pretty unanswered.  Instinct alright, but the question remains: HOW?  \n\nNow, there are two means that have been found to be apparently of importance for migrating birds.  One is magnetic field orientation, the other is visual orientation.  Both seem to be involved partially or exclusively, but how exactly they work remains a bit of a mystery.\n\nIn order for an animal to orient itself along the magnetic field of the earth, it has to somehow sense the field.  This can either work by means of having magnetic substances in the body, that will align according to the magnetic field.  Their alignment must then be sensed by the organism.  Some organisms have magnitide enclosed in their body that serves this function.  However, in birds nothing like it has been found.  Nevertheless, birds do use magnetic fields, and so the question remains: HOW?\n\nElasmobranchs (sharks, skates, and rays) actually orient themselves according to the earth's magnetic field using electric currents.  It's a simple but very impressive physiological achievement.  If you move a charge through a standing magnetic field, you will induce an electric current.  This is due to the Lorentz force, which will act on the charge (F = q v B sinØ).  The right hand rule will give you the direction of the Lorentz force.  If the shark swims in an eastern direction, the Lorentz force will pull upwards, so that the direction of the induced electric field is a dorso-ventral one (i.e., one pol is on the back of the animal, from where the current flows to the other pol on the belly of the shark).  If the shark were to swim the opposite direction, the electric current would run the other way.  With its electrosensitive organs (Ampullae of Lorenzi), the sahrk can sense the direction of the current and figure out which direction it swims.  It's an electromagnetic compass.  However, birds have no electrosensitive receptors...\n\nNow, birds also use visual cues.  These seem to be primarily stars, which is of course great for navigation.  Landmarks, like mountains etc. may also play a role.  \n\nBut again, how this works in detail is not fully understood.  Let me know once you figure it out!!!
257089
Depending on the fish there could be different obstacles. Certain sharks must continually swim to pass water over there gills to not suffocate. Also in certain shallow water mangroves oxygen depleted water can be another obtacle (except for the lemon shark which can survive better in low oxygen water). I also believe polluted water, such as oil spills and the like, can be perhaps the biggest obstacle of all the fish will face in the respiration process especially around coastal areas.
424120
yes.. \n\nyou body adapts to the sea movement and then it takes some time for it to adapt back
29544
Sharks have two senses that many animals do not have:\n\nElectroreception: The Ampullae of Lorenzini are small pits in the head that detect electricity. The shark has the greatest electricity sensitivity known in all animals. This sense is used to find prey hidden in sand in bottom feeding sharks, by detecting the nerve impulses. It is this sense that sometimes confuses a shark into attacking a boat: when the metal interacts with salt water, sharks can detect the resultant electrical charge from over one mile away. \nLateral line - This system is found in most fishes, including sharks. It is used to detect motion or 'sound' in the water. The shark uses this to detect other organisms moving, especially wounded fish. The shark can 'hear' frequencies in the range of 25 to 50 Hz using this sense.\n\nHOW TO SWIM WITH SHARKS: A PRIMER \nVoltaire Cousteau\n\n\n--------------------------------------------------------------------------------\n\nForward\n\nActually, nobody wants to swim with sharks. It is not an acknowledged sport and it is neither enjoyable nor exhilarating. These instructions are written primarily for the benefit of those, who, by virtue of their occupation, find they must swim and find that the water is infested with sharks.\n\nIt is of obvious importance to learn that the waters are shark infested before commencing to swim. It is safe to say that this initial determination has already been made. If the waters were infested, the naïve swimmer is by now probably beyond help; at the very least, he has doubtless lost any interest in learning how to swim with sharks.\n\nFinally, swimming with sharks is like any other skill: It cannot be learned from books alone; the novice must practice in order to develop the skill. The following rules simply set forth the fundamental principles which, if followed will make it possible to survive while becoming expert through practice.\n\nRules\n\nAssume all unidentified fish are sharks. Not all sharks look like sharks, and some fish that are not sharks sometimes act like sharks. Unless you have witnessed docile behavior in the presence of shed blood on more than one occasion, it is best to assume an unknown species is a shark. Inexperienced swimmers have been badly mangled by assuming that docile behavior in the absence of blood indicates that the fish is not a shark. \nDo not bleed. It is a cardinal principle that if you are injured, either by accident or by intent, you must not bleed. Experience shows that bleeding prompts an even more aggressive attack and will often provoke the participation of sharks that are uninvolved or, as noted above, are usually docile. \nAdmittedly, it is difficult not to bleed when injured. Indeed, at first this may seem impossible. Diligent practice, however, will permit the experienced swimmer to sustain a serious laceration without bleeding and without even exhibiting any loss of composure. This hemostatic reflect can, in part, be conditioned, but there may be constitutional aspects as well. Those who cannot learn to control their bleeding should not attempt to swim with sharks, for the peril is too great. \nThe control of bleeding has a positive protective element for the swimmer. The shark will be confused as to whether or not his attack has injured you and confusion is to the swimmer's advantage. On the other hand, the shark may know he has injured you and be puzzled as to why you do not bleed or show distress. This also has a profound effect on sharks. They begin to question their own potency or, alternatively, believe the swimmer to have supernatural powers.\n\nCounter any aggression promptly. Sharks rarely attack a swimmer without warning. Usually there is some tentative, exploratory aggressive action. It is important that the swimmer recognize that this behavior is a prelude to an attack and takes prompt and vigorous remedial action. The appropriate countermove is a sharp blow to the nose. Almost invariably this will prevent
474404
They are called Zambezi Sharks and they swim in the Zambezi river in Africa. I think they are really Bull Sharks that can swim in salt and fresh water.\n\nI dont know if i spelt Zambezi correctly.
761847
Some of them are buoyant and sleep floating on the surface breathing air. Others can do what in humans is comparable to the "dead man's float" where you are under the water motionless then tilt your head back only, rise to the surface to breathe, tilt it back and resubmerge. Hippos can do this without ever waking up so I assume some marine mammals can too.
343823
it is possible, depends on how heavy ur leakage is and how far the sharks are from you, but thats just the thing.. you never kno until they BITE...