1 00:00:01,920 --> 00:00:04,320 Speaker 1: Welcome to brain Stuff, a production of I Heart Radio, 2 00:00:06,280 --> 00:00:10,760 Speaker 1: Hey brain Stuff Lauren Vogel Bam. Here, sharks take doing 3 00:00:10,800 --> 00:00:13,680 Speaker 1: the wave to a whole new level. They swim by 4 00:00:13,760 --> 00:00:17,319 Speaker 1: waving their body inside to side curves. It starts with 5 00:00:17,360 --> 00:00:20,759 Speaker 1: the head turning first one way, then another. The movement 6 00:00:20,840 --> 00:00:24,759 Speaker 1: ripples down their torpedo shaped body, pushing the water away 7 00:00:24,880 --> 00:00:29,159 Speaker 1: and providing forward propulsion. Last comes the tail, with the 8 00:00:29,200 --> 00:00:32,200 Speaker 1: fins shaped to allow them to move quickly and achieve 9 00:00:32,280 --> 00:00:37,479 Speaker 1: immense liftoff or propulsive downward thrust. Obviously, a shark has 10 00:00:37,520 --> 00:00:40,120 Speaker 1: to swim to catch its prey, meet its mates, and 11 00:00:40,200 --> 00:00:43,360 Speaker 1: avoid its predators. But does a shark have to swim 12 00:00:43,640 --> 00:00:47,199 Speaker 1: just to stay alive. You may have heard that a 13 00:00:47,240 --> 00:00:50,480 Speaker 1: shark will drown if it stops moving, an idea that's 14 00:00:50,479 --> 00:00:53,880 Speaker 1: been sited everywhere from biology textbooks to Ripley's Believe it 15 00:00:53,960 --> 00:00:57,800 Speaker 1: or not. This theory came about by comparing sharks, which 16 00:00:57,800 --> 00:01:02,160 Speaker 1: are classified as cartilaginous fish, to bony fish, which have 17 00:01:02,320 --> 00:01:05,880 Speaker 1: many more muscles around their breathing apparatus is the gills. 18 00:01:07,440 --> 00:01:10,959 Speaker 1: To understand why this distinction is important, let's take a 19 00:01:11,000 --> 00:01:14,640 Speaker 1: look at how sharks and other fish breathe. To breathe, 20 00:01:14,760 --> 00:01:18,679 Speaker 1: sharks must remove oxygen from the water around them. The 21 00:01:18,760 --> 00:01:22,520 Speaker 1: water enters the shark's mouth, its nose being used exclusively 22 00:01:22,560 --> 00:01:25,720 Speaker 1: for smell, and then the water flows over the gills. 23 00:01:26,400 --> 00:01:30,600 Speaker 1: Inside those gills, there are hundreds of feathery gill filaments. 24 00:01:30,600 --> 00:01:34,280 Speaker 1: Each filament, in turn has thousands of leaf like lamellie 25 00:01:34,440 --> 00:01:38,399 Speaker 1: or flaps, which contain blood vessels. The blood absorbs the 26 00:01:38,400 --> 00:01:41,759 Speaker 1: oxygen from the incoming water, and the excess water flows 27 00:01:41,760 --> 00:01:45,720 Speaker 1: back out of the shark's body through gill slits. Sharks 28 00:01:45,800 --> 00:01:48,680 Speaker 1: have five to seven pairs of gill slits, depending on 29 00:01:48,720 --> 00:01:53,639 Speaker 1: the species. Using this method, sharks can extract about eighty 30 00:01:53,680 --> 00:01:56,720 Speaker 1: per cent of oxygen out of the meager one percent 31 00:01:56,800 --> 00:01:59,920 Speaker 1: of free oxygen that's present in the water. To compare, 32 00:02:00,240 --> 00:02:02,080 Speaker 1: the air that we breathe is made up of about 33 00:02:02,920 --> 00:02:09,320 Speaker 1: available oxygen, but human lungs only extract about of that anyway, 34 00:02:09,360 --> 00:02:12,959 Speaker 1: to maintain a steady flow, the shark constantly needs to 35 00:02:13,000 --> 00:02:17,120 Speaker 1: be taking in water. But does it have to constantly 36 00:02:17,200 --> 00:02:20,680 Speaker 1: swim to take in this water? A scientist's thought so, 37 00:02:20,919 --> 00:02:24,360 Speaker 1: because other fish seemed to have the equipment to actively 38 00:02:24,440 --> 00:02:27,360 Speaker 1: pump the water through their mouth and over their gill slits, 39 00:02:27,840 --> 00:02:32,120 Speaker 1: whereas sharks looked less developed. But that doesn't account for 40 00:02:32,160 --> 00:02:34,960 Speaker 1: sharks that just kind of chill, like angel sharks and 41 00:02:35,040 --> 00:02:38,360 Speaker 1: nurse sharks. It turns out that not all sharks have 42 00:02:38,480 --> 00:02:43,200 Speaker 1: to stay moving to breathe. The oldest sharks, the ancestors 43 00:02:43,240 --> 00:02:46,640 Speaker 1: of more modern sharks, didn't have to constantly swim in 44 00:02:46,760 --> 00:02:50,360 Speaker 1: order to breathe. Rather, they pumped water through their mouth 45 00:02:50,440 --> 00:02:54,560 Speaker 1: and over their gills. This method is known as buckle pumping, 46 00:02:54,960 --> 00:02:57,840 Speaker 1: named for the buckle or cheek muscles that pull the 47 00:02:57,880 --> 00:03:01,400 Speaker 1: water into the mouth and over the gills. Many sharks 48 00:03:01,400 --> 00:03:04,680 Speaker 1: retain this method today, such as the aforementioned nurse and 49 00:03:04,760 --> 00:03:07,960 Speaker 1: angel sharks, as well as carpet sharks, eskates, and rays. 50 00:03:08,040 --> 00:03:11,639 Speaker 1: The sharks cousins also breathe this way. These species tend 51 00:03:11,720 --> 00:03:14,160 Speaker 1: to spend most of their time laying on the bottom 52 00:03:14,160 --> 00:03:18,680 Speaker 1: of the ocean floor. Many of these sharks are dorso 53 00:03:18,800 --> 00:03:22,880 Speaker 1: ventrally flattened, that is, sort of squashed looking along the 54 00:03:22,960 --> 00:03:26,919 Speaker 1: length of their Backlike the angel shark, they have stronger 55 00:03:27,000 --> 00:03:30,160 Speaker 1: muscles in the face. These sharks might also have a 56 00:03:30,160 --> 00:03:33,639 Speaker 1: more prominent spircle, which is a tube behind the eyes. 57 00:03:34,320 --> 00:03:36,360 Speaker 1: When a shark is buried at the bottom of the 58 00:03:36,360 --> 00:03:39,920 Speaker 1: ocean floor and can't breathe through its mouth, the spircle 59 00:03:40,040 --> 00:03:44,040 Speaker 1: can pull in water instead. As sharks evolved and became 60 00:03:44,040 --> 00:03:48,680 Speaker 1: more active, however, buckle pumping became secondary. It was simply 61 00:03:48,840 --> 00:03:52,000 Speaker 1: more energy efficient to take in water while swimming, in 62 00:03:52,080 --> 00:03:54,920 Speaker 1: effect ramming the water into the mouth and letting it 63 00:03:54,920 --> 00:03:58,200 Speaker 1: flow through the gill slits. This method of breathing is 64 00:03:58,280 --> 00:04:02,400 Speaker 1: known as a ram ventilation. Most sharks can alternate between 65 00:04:02,480 --> 00:04:05,520 Speaker 1: buckle pumping and ram ventilation depending on what they're doing. 66 00:04:06,040 --> 00:04:08,720 Speaker 1: When they start swimming fast enough to force the water 67 00:04:08,760 --> 00:04:11,240 Speaker 1: in more quickly than they could pump it, then they 68 00:04:11,360 --> 00:04:14,720 Speaker 1: stop pumping. The sand tiger shark is an example of 69 00:04:14,760 --> 00:04:18,560 Speaker 1: a shark that switches back and forth. Some sharks, however, 70 00:04:18,640 --> 00:04:21,880 Speaker 1: have completely lost the ability to breathe by buckle pumping, 71 00:04:22,400 --> 00:04:25,040 Speaker 1: and these are the sharks that will indeed drown if 72 00:04:25,040 --> 00:04:29,120 Speaker 1: they stop swimming and thus ramming water. These sharks are 73 00:04:29,160 --> 00:04:33,719 Speaker 1: known as obligate ram breathers or obligate ram ventilators, and 74 00:04:33,839 --> 00:04:36,880 Speaker 1: only about two dozen of the four hundred identified shark 75 00:04:36,920 --> 00:04:41,520 Speaker 1: species are required to maintain this forward swimming motion. These 76 00:04:41,560 --> 00:04:44,880 Speaker 1: include the great white shark, the mako shark, the salmon shark, 77 00:04:45,000 --> 00:04:49,920 Speaker 1: and the whale shark. So do these obligate ram breathers 78 00:04:50,040 --> 00:04:54,160 Speaker 1: ever get a break? Aren't they tired? As it turns out, 79 00:04:54,360 --> 00:04:57,120 Speaker 1: it's more work for these sharks to remain still than 80 00:04:57,160 --> 00:04:59,960 Speaker 1: it is to swim. In a study of lemon shark 81 00:05:00,120 --> 00:05:04,440 Speaker 1: switch switch between breathing methods, juveniles breathed six percent more 82 00:05:04,440 --> 00:05:08,440 Speaker 1: efficiently when moving than when resting, even when resting so 83 00:05:08,480 --> 00:05:11,000 Speaker 1: that the current allowed the water to flow directly into 84 00:05:11,000 --> 00:05:14,560 Speaker 1: their mouths. That's not to say that these sharks don't 85 00:05:14,600 --> 00:05:17,719 Speaker 1: catch a break every now and then. For obvious reasons, 86 00:05:17,800 --> 00:05:19,720 Speaker 1: it can be hard to keep track of a shark 87 00:05:19,800 --> 00:05:23,360 Speaker 1: that's constantly swimming, so it's difficult for scientists to know 88 00:05:23,600 --> 00:05:27,599 Speaker 1: how or when they rest. An experiment with a small shark, 89 00:05:27,720 --> 00:05:31,520 Speaker 1: the spiny dogfish, indicated that swimming is coordinated by the 90 00:05:31,560 --> 00:05:35,000 Speaker 1: spinal cord, not the brain, so sharks may be able 91 00:05:35,040 --> 00:05:37,839 Speaker 1: to shut down their brain and rest while still swimming. 92 00:05:39,320 --> 00:05:42,080 Speaker 1: Sharks in needisome rest may also take advantage of the 93 00:05:42,120 --> 00:05:44,599 Speaker 1: factors that affect the amount of oxygen in the water, 94 00:05:44,800 --> 00:05:48,320 Speaker 1: such as salinity, temperature, and even the time of day. 95 00:05:48,720 --> 00:05:51,840 Speaker 1: In the nineteen seventies, scientists investigated what came to be 96 00:05:51,920 --> 00:05:54,760 Speaker 1: known as the Caves of the Sleeping Sharks in Mexico. 97 00:05:55,560 --> 00:05:59,200 Speaker 1: Inside the caves were motionless reef sharks, which are normally 98 00:05:59,240 --> 00:06:03,760 Speaker 1: obligate ventilators. The scientists determined that the water in the 99 00:06:03,800 --> 00:06:08,560 Speaker 1: caves had an extremely high amount of oxygen and reduced salinity. 100 00:06:09,080 --> 00:06:12,400 Speaker 1: These conditions likely made it easier for even these sharks 101 00:06:12,440 --> 00:06:16,320 Speaker 1: to breathe without moving. They may not have been asleep 102 00:06:16,400 --> 00:06:19,320 Speaker 1: like humans, their eyes were open, for one thing, but 103 00:06:19,440 --> 00:06:22,760 Speaker 1: it does appear that sharks can get some rest, and 104 00:06:22,839 --> 00:06:25,599 Speaker 1: many other reef sharks have also been observed motionless at 105 00:06:25,600 --> 00:06:29,800 Speaker 1: the bottom even outside of caves. Scientists still aren't exactly 106 00:06:29,880 --> 00:06:37,960 Speaker 1: sure how they can do this. Today's episode is based 107 00:06:37,960 --> 00:06:40,760 Speaker 1: on the article will a shark drown if it stops moving? 108 00:06:40,880 --> 00:06:44,160 Speaker 1: On how stuffworks dot Com, written by Molly Edmonds. Brain 109 00:06:44,200 --> 00:06:46,360 Speaker 1: Stuff is production of I Heart Radio in partnership with 110 00:06:46,400 --> 00:06:48,960 Speaker 1: how stuff works dot Com and is produced by Tyler Klang. 111 00:06:49,400 --> 00:06:52,080 Speaker 1: Four more podcasts my heart Radio, visit the i heart 112 00:06:52,120 --> 00:06:54,960 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 113 00:06:54,960 --> 00:06:55,680 Speaker 1: favorite shows.