# Do Sharks Really Have to Swim? **URL:** \ **Category:** Factual Questions\ **Created:** [July 17, 2004, 12:23am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516 "2004-07-17T00:23:28Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [July 17, 2004, 12:23am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/1 "2004-07-17T00:23:28Z")
All the reference books I’ve seen and the links in Google state that sharks must continually swim to prevent sinking. However, I recall (vaguely) seeing a TV program that showed that this is not necessarily so, as the wave action of the waters will prevent them from sinking. So, what’s the straight dope? ---
**Author:** ![legion](https://avatars.discourse-cdn.com/v4/letter/l/838e76/32.png) [@legion](https://boards.straightdope.com/u/legion)\ **Post date:** [July 17, 2004, 12:27am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/2 "2004-07-17T00:27:07Z")
I had always believed that they had to swim in order to force water through their gills. I’ve seen film of stationary sharks, but only in places where the current does the job for them. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 17, 2004, 12:40am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/3 "2004-07-17T00:40:49Z")
Well sharks can could certainly be kept at a constant height in the water column without swimming if there was a very fast flow of water over their bodies, much as a pane can ‘hover’ in a very fast wind without actually moving. But that situation is almost never going to arise. For most sharks most of the time there will be no ‘wave action’ or any other appreciable water current to keep them up, and sharks lack a swim bladder. So the answer is that for almost any shark at almost any time it will need to keep moving or it will sink. For all practical purposes sharks need to keep swimming or they will sink. As for sharks needing to swim to breathe, there isn’t any solid evidence for such a belief. Sharks use quite a bit more energy trying to breathe if they don’t keep moving, but it’s nowhere near enough to suggest they would ever suffocate as a result of lying on the bottom. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 17, 2004, 4:12am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/4 "2004-07-17T04:12:02Z")
There are a lot of different sharks. Some have to swim, some don’t. Great whites, for example, have to keep swimming. A nurse shark on the other hand is quite happy sitting motionless on the bottom. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [July 17, 2004, 4:18am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/5 "2004-07-17T04:18:21Z")
Actually depending on the species some sharks do need to either keep moving or have water flowing through the gills from the current. Ram ventillation is used by many large fast moving pelagic fish. Tuna use it, so do some sharks. The sharks don’t have operculums to pump water through the gills, and thus need another way to get water flowing through the gills efficiently. Ram ventilation is simply swimming with the mouth open. Not all sharks need to do it however. Many species can lay on the bottom for hours on end gently huffing enough water to breath. For the more active species that ain’t enough. Sharks compensate for no swim bladder by having huge oily livers for bouyancy, but that’s not usually enough either. Many species have fins and body shapes that help keep them from sinking as they swim such as the orientation of the pectorals, shape of tail, and having those odd noses that will deflect the water down (& push them up) as they move forwards. Of course there are also species that are bottom dwellers without such features. Just swimming forward helps some active sharks both prevent sinking and aids in supplying enough oxygen to keep it all going. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 17, 2004, 12:50pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/6 "2004-07-17T12:50:45Z")
Mike can you provide a reference for your claims that some sharks need to swim to get enough oxygen? All the studies I’ve seen show that sharks use a lot of energy to breath actively but I’ve never seen any that show that suffocation would result. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [July 17, 2004, 12:59pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/7 "2004-07-17T12:59:22Z")
There was a Jacques Cousteau special called _The Sleeping Sharks of [Someplace]_ that mentioned the belief that sharks had to keep swimming to breathe, and that these sharks didn’t. Might have been some other than Cousteau, but there was definitely a documentary. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [July 17, 2004, 4:11pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/8 "2004-07-17T16:11:08Z")
> [@Johnny L.A.](#): > > There was a Jacques Cousteau special called _The Sleeping Sharks of [Someplace]_ that mentioned the belief that sharks had to keep swimming to breathe, and that these sharks didn’t. Might have been some other than Cousteau, but there was definitely a documentary. On a related note see [“40 Winks Under the Sea”](http://www.elasmo-research.org/education/topics/b_40_winks.htm) by the ReefQuest Centre for Shark Research - fascinating article. Goes into a lot of detail about the issues discussed in this thread. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 17, 2004, 6:24pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/9 "2004-07-17T18:24:12Z")
> [@Johnny L.A.](#): > > There was a Jacques Cousteau special called _The Sleeping Sharks of [Someplace]_ that mentioned the belief that sharks had to keep swimming to breathe, and that these sharks didn’t. Might have been some other than Cousteau, but there was definitely a documentary. You don’t need to go too far to do the Jacques Costeau number. In places as close as the Florida Keys, one can find many sharks apparently sleeping underneath coral bulbs, wrecks, outcroppings, etc. Usually (as has been reported) these are nurse sharks, some quite large. They will stay there for quite a while, not moving, seemingly dead to the world. You can wake them up and scoot them along, so as to prove that they are, indeed, sleeping and not dead. And you don’t need intense SCUBA gear, either. You can observe this just skin diving. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 18, 2004, 3:14am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/10 "2004-07-18T03:14:25Z")
> [@Blake](#): > > As for sharks needing to swim to breathe, there isn’t any solid evidence for such a belief. Sharks use quite a bit more energy trying to breathe if they don’t keep moving, but it’s nowhere near enough to suggest they would ever suffocate as a result of lying on the bottom. Could you please provide a cite for this, particularly the relative energy demands? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 18, 2004, 5:12am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/11 "2004-07-18T05:12:54Z")
Here are some cites: > **[How Sharks Work](https://animals.howstuffworks.com/fish/sharks/shark1.htm)** > > There are over 400 species of sharks, but what makes a shark a shark - shark anatomy. Learn about shark anatomy and learn how these creatures work. > [@](#): > > Some sharks have a gill pump, a set of muscles that suck in water and push it past the gills. This works something like our lungs – the shark can continuously gather oxygen while it is in a still position. Most sharks also extract oxygen using ram ventilation, passing water over the gills by moving forward. Some highly-active sharks depend on ram ventilation almost entirely, which means they stay in motion most of the time! [http://homepages.tig.com.au/~idal/sharkfaq.htm](http://homepages.tig.com.au/~idal/sharkfaq.htm) > [@](#): > > Sharks do not have swim bladders and will sink if they stop swimming. Bottom-dwelling sharks need not swim constantly because they can pump water over their gills in order to breathe, but sharks which inhabit the open ocean have to swim to keep water flowing over their gills. [http://www.tnaqua.org/Animals/Fish%20ID/Bonnethead\_shark.htm](http://www.tnaqua.org/Animals/Fish%20ID/Bonnethead_shark.htm) > [@](#): > > Sharks breathe by extracting oxygen from seawater as it passes over their gills; if they stop swimming, the water circulation needed for respiration would cease, resulting in suffocation. Other sharks, like the nurse shark and blacktip reef shark, are capable of pumping water over their gills as they rest on the ocean bottom. [http://www.biosci.ohio-state.edu/~eeob/eeob405/labs/sharkswimmingQ.html](http://www.biosci.ohio-state.edu/~eeob/eeob405/labs/sharkswimmingQ.html) (page is too short to quote) [http://www.accessexcellence.org/LC/ST/Sharks/index.html](http://www.accessexcellence.org/LC/ST/Sharks/index.html) > [@](#): > > e-Mail QUESTION: Do all species/or some species of shark have to keep moving in order to respire or is this a myth? > > ANSWER: No, all species do not have to keep moving in order to respire. In fact, more species can rest on the bottom than not. There are two methods that sharks use to extract oxygen from water. By using their pharynx as a buccal pump some species are able to pump water over their gills. Once the animal begins to move at about 1-2 body lengths per second, they simply open their mouth and do what is called “ramjet” ventillation. Some species such as the mako, great hammerhead, silky and other open ocean sharks are obligate ramjet ventillators, but as I said, many species have no problem pumping water over their gills. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 18, 2004, 5:15am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/12 "2004-07-18T05:15:55Z")
Well here is one online reference. There are many more print references readily available if you want to take the time to do a search on Ovid or similar. > [@](#): > > As part of an ambitious ten-year project on the role of the Lemon Shark in the shallow waters of Bimini, a University of Miami team led by Samuel Gruber has studied numerous aspects of Lemon Shark biology, both in the field and in the laboratory. Gruber’s team confirmed that adult Lemon Sharks lying quietly on the bottom for extended periods actively pump water over their gills. They noted that the sharks typically prop themselves up on their pectoral fins and face into the prevailing current; these behaviors may help them breathe easier. Manometry experiments in Gruber’s laboratory have revealed that, even facing into the current and propped up on their fins, juvenile Lemon Sharks use about 9% more oxygen actively respiring than they do if swimming in the water column and relying on passive ram-jet ventilation. In other words, a Lemon Shark has to work harder lying on the bottom than it does swimming. So, whatever they’re doing, it ain’t restful. [http://www.elasmo-research.org/education/topics/b\_40\_winks.htm](http://www.elasmo-research.org/education/topics/b_40_winks.htm) Frankly Colibri I’n surprised that a fellow biologist would find it all surprising that sharks that normally rely on ramjet ventilation would use more energy when stationary. However that is beside the point. I would be very interested to see any actual evidence that any species of shark needs to keep moving in order to avoid suffocation. All the research I have seen says that there is a greater energy use for many sharks while stationary but that it is nowhere near enough to case any problems. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 18, 2004, 5:20am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/13 "2004-07-18T05:20:35Z")
engineer\_comp\_geek those pages just repeat the commonly accepted assertion that some sharks need to swim to breathe. I would very much like to see some evidence that supports such assertions. A 9% energy use increase above ‘resting’ levels is hardly enough to warrant fears of immediate death. Humans experience greater energy increases going from sitting to walking and we are in no danger of incurring any oxygen debt when we walk around. It’s obviously going to be hard to get a large pelagic shark and strap it down to test the theory one way por the other, but I’d be interested to know if there is any hard data at all to support the belief that any shark species dies when immobilised. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [July 18, 2004, 10:55am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/14 "2004-07-18T10:55:26Z")
Here are a few pages talking about obligate ram ventilation in some shark species: [1](http://www.fathom.com/course/21701777/session1.html) [2](http://www.kluweronline.com/article.asp?PIPS=310189&PDF=1) [3](http://www.dynasty-marine.com/manuscript.html) [4](http://www.sefscpanamalab.noaa.gov/docs/JC03JEMB.pdf) Many shark species are _facultative_ ram ventialtors, and some are _obligate_ ram ventilators. Obigates cannot meet absorb enough oxygen from the water to meet requirements without swimming (or having water flowing into the mouth). The meaning is kinda built right into the term… “obligate” ram ventilators. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 18, 2004, 5:18pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/15 "2004-07-18T17:18:07Z")
> [@Blake](#): > > It’s obviously going to be hard to get a large pelagic shark and strap it down to test the theory one way por the other, but I’d be interested to know if there is any hard data at all to support the belief that any shark species dies when immobilised. As **mmmiikkkee** indicates, many sites on the web, including reputable ones like the American Elasmobranch Society and the British Museum of Natural History, indicate that some species of pelagic sharks are **obligate** ram ventilators, and state that they must swim in order to breathe. One specific species in which this is stated to be true is the [Porbeagle _Lamna nasus_](http://new-brunswick.net/new-brunswick/sharks/species/porbeagle.html). Another [cite](http://www.sefscpanamalab.noaa.gov/shark/pdf%5C1514_C07.pdf) > [@](#): > > Elasmobranchs vary in their ability to pump water over their gills through buccal pumping. Variation in this ability is directly linked to variability in metabolism and lifestyle. For example, elasmobranchs in Orders Heterodontiformes and Rajiiformes are relatively less active and demersal, and oxygenate their gills via buccal pumping. However, more active pelagic species such as those found in Orders Myliobatiformes and Carcharhiniformes (Families Carcharhinidae and Sphyrnidae) utilize ram ventilation, which allows the organism to ventilate its gills by holding the mouth open while swimming (Brown and Muir, 1970). A shift to this mode occurs when swimming velocity reaches a rate at which flow volume is adequate to supply respiratory needs. Among other species of elasmobranchs particularly lamnid, carcharhinid, and sphyrnid sharks, branchiostegal systems are reduced and thus inadequate to force water over the gills when forward movement has slowed or movement has ceased. These sharks are termed obligate ram ventilators because they must maintain constant forward movement for respiration (Roberts, 1978). Like tunas and mackerels, these sharks possess morphological, behavioral, and physiological adaptations for continuous activity (Parsons, 1990). Other sites mention that pelagic sharks will suffocate if prevented from swimming if confined in nets or prevented from swimming. One example is [here](http://www.globeandmail.com/servlet/ArticleNews/front/RTGAM/20030116/wshar0116/Front/homeBN/breakingnews) > [@](#): > > The culprits, say the researchers, are fishermen who aren’t even looking for sharks. Rather, they bait as many as 1,000 hooks on a trailing line — known as a longline — to catch tuna and swordfish. > > They also accidentally snare sharks, which often suffocate while on the hook because oxygen-bearing water is no longer flushing past their gills. > [@Blake](#): > > Frankly Colibri I’n surprised that a fellow biologist would find it all surprising that sharks that normally rely on ramjet ventilation would use more energy when stationary. Of course I said nothing of the kind. It is of course reasonable that a shark will require more energy to breathe when stationary. What I asked you for a cite of was evidence for your assertion that: > [@Blake](#): > > it’s nowhere near enough to suggest they would ever suffocate as a result of lying on the bottom. The cite you offer does not provide such evidence. For one thing, the 9% increase in metabolic demand for Lemon Sharks is while they are “facing into the current and propped up on their fins;” in still water their metabolic demand will be greater. Also, the Lemon Shark is not a particularly specialized ram-ventilator. The Mako Shark or the Porbeagle are more typical of this group. As indicated in the article I cited, these kinds of species have a reduced brachystegial apparatus and hence less capacity to breathe when stationary. **Blake,** please cite the titles of the “many more print references readily available” that you mention. I have on-line access to many scientific journals and can also obtain them from my library at work. Unfortunately you have a history here of making statements that contradict standard textbook information (as in this case), and when asked to provide cites either posting not particularly relevant ones (like the one on the Lemon Shark), or else disappearing entirely from the thread. If you are going to dispute information that appears in a large number of journal articles as well as on authoritative websites (specifically that at least some pelagic sharks are obligate ram-ventilators), the onus is on you to provide support for your position. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 19, 2004, 9:50am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/16 "2004-07-19T09:50:19Z")
Unfortunatlely Colibri oyu have a history here of speaking as though you were Cecil himself. Furthermore you frequently ask for references and then simply ignore them. I have provided a reference which supports exactly what I said. I’m sure you have access to Ovid or Blackwell or similar to find further articles yourself. What I have said has been fully supported, as usual. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [July 19, 2004, 8:54pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/17 "2004-07-19T20:54:30Z")
> [@](#): > > As for sharks needing to swim to breathe, there isn’t any solid evidence for such a belief. Sharks use quite a bit more energy trying to breathe if they don’t keep moving, but it’s nowhere near enough to suggest they would ever suffocate as a result of lying on the bottom. Unfortunately you have not provided _any_ cites for 2/3 of this, which seems to be your main point; that there is no such thing as an obligate ram ventilating shark species anywhere in the world and that all shark species’ physiological adpatations for breathing can be accurately generalized as being the same; ie a grey reef shark ventilates the same as a lemon shark. We await your cites disproving every (or any) scientific reference to obligate ram ventilators and of differences in ventilation strategies existing between species. > [@](#): > > What I have said has been fully supported, as usual :D:D:D You said three things in the top quote, but the only one that was referenced was the irrelevent one… as usual. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 19, 2004, 11:23pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/18 "2004-07-19T23:23:44Z")
What can be characterized as spirited debate and challenge is slipping dangerously close to a pissing contest. I’m waiting for “nyah nyah - did too,” “did not,” “did too…” Mods - stay tuned. xo C. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [July 19, 2004, 11:50pm UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/19 "2004-07-19T23:50:36Z")
LOL, we’re simply asking for references showing established science and definitions to be invalid. Until then, (or more preferably _instead_)the answer to the OP is: Most sharks do need to keep moving in order not to sink, although many rest on the bottom anyways so it’s no big deal. A side note is that most sharks don’t need to swim to breath, but there are a few specialized species that do. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 20, 2004, 2:53am UTC](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516/20 "2004-07-20T02:53:13Z")
> [@Blake](#): > > Unfortunatlely Colibri oyu have a history here of speaking as though you were Cecil himself. Furthermore you frequently ask for references and then simply ignore them. I have provided a reference which supports exactly what I said. I’m sure you have access to Ovid or Blackwell or similar to find further articles yourself. What I have said has been fully supported, as usual. Well, I may not be Cecil, but I do regularly help him out on questions of this kind. He has cited me by name in four of his columns (and I have assisted with several others). Cecil has also appointed me Straight Dope Curator of Critters. If The Master _were_ answering the OP, there’s a good chance he would ask my opinion on it. I think **mmmiiikkkee** has pretty well summed up the quality of your response. And you don’t do anything for your credibility by claiming that you know of “many more print references readily available”on the subject, and then not being able to produce one single example when asked for them - especially when you pulled exactly the same stunt in another thread last week. (I’ll be happy to provide the link if you want it.) As far as me ignoring your references, you’ve got to be kidding. I responded directly to the only one you have cited in this thread. Meanwhile, you have ignored **mmmiikkkee’s** and mine. In other threads I have often responded to your points with cites of peer-reviewed literature, which you have rarely if ever responded to substantively. In fact, on several occasions you have simply abandoned the thread. > [@CC](#): > > What can be characterized as spirited debate and challenge is slipping dangerously close to a pissing contest. I’m waiting for “nyah nyah - did too,” “did not,” “did too…” Mods - stay tuned. xo C. You don’t seem to understand either GQ or how to evaluate evidence. **Blake** made a statement that contradicts a large number of authoritative sources on the subject, and then has been unable to back it up with any references. I wouldn’t characterize what he is doing as “debating.” [Next page](https://boards.straightdope.com/t/do-sharks-really-have-to-swim/255516.md?page=2)