Testing if Sharks Can Smell a Drop of Blood

Mark Rober
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    Scientific proof Pixar sits on a throne of lies. Thanks to Bose for their support and for the dopest headphones I've ever worn: https://bose.life/markrober

    Also, thanks to Discovery for putting my life in danger.
    #SharkWeek begins July 28 only on Discovery
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    Links for the build instructions: https://www.dropbox.com/s/iqn14ydzqafhws5/SharkBait_Manual_PartsList.pdf?dl=0

    Sean's Hodgin's channel who did most of the heavy lifting for making the boxes: https://www.youtube.com/channel/UCE-bw6PRKuDlH6fP1mP4nOw

    Pump animation made by the talented Jared Owens:
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    More info that was promised-
    What is likely happening is that the sharks can smell the blood but it's just not in a quantity that is interesting to them especially since they don't love human blood that much (btw, I spoke with a marine biologist and mammal blood is all the same from a chemical marker stand point so cow blood is a suitable substitute for human blood). If I did the experiment again, I would want to test human blood vs. fish blood.

    This is the most definitive study done to date in a control lab environment on what is least and most interesting to them: The Biology of Sharks and Rays Peter A. Klimley and Steven Oerding; ISBN-13: 9780226442495. Particularly pages 134-140. Figure 6.7; Table 6.2


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    Summary: I've always wanted to test if sharks can really smell a single drop of blood in the water from 1 mile away. So I went to the Bahamas in shark infested waters and set up an experiment to get to the bottom of things.



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    Published


    I texted this clip to my wife who wanted proof I wasn't doing anything stupid on a recent trip to the Bahamas Now if you're wondering what my feet are doing in shark-infested waters with a bucket of blood 20 miles away from any land Well, that comes down to a conversation. I had with my friends at the Discovery Channel six months ago They told me Shark Week is coming up and they want to know what I would do if they could put me in the middle of the ocean on a boat surrounded by sharks for as long as I can remember I've always wanted to test if sharks can really smell a drop of blood in the water from a mile away Now before you say Mythbusters already did this They kind of did this as you can see to test this they poked their fingers and then stuck them in a barrel with these Tiny lemon sharks and since they didn't really seem to turn around and look at their fingers They said it was busted now I'm friends with both Kari and Adam, but I think even they would have been at least in this case The methodology was less than scientifically rigorous so I came up with a more robust test procedure built some NASA great hardware for the experiment hopped on a plane and then a Speedboat and soon enough. I was 20 miles offshore of the Bahamas To kick things off I sat down with my marine biologist shark diving expert friend Luke Tipple and explained my plan in eventually Eventually I plan to test just how far they could smell a single drop of blood in the water But first I wanted proof that they actually preferred blood over any other scent So for my first experiment I plan to put four surfboards in the water equa-distant from the back of the boat each board would host two litres of a different liquid that we would pump into the ocean over the course of an hour then using A three meter radius around each board as a gauge we would use drone footage and count how many sharks went over to check out? Each board. So this board would be fish oil, which I heard was a general attractant for lots of fish Then we would have cows blood here Then sea water here as a control to make sure the Sharks weren't just interested in the surfboard and then finally urine I've heard From surfers that a lot of them won't pee in their wetsuits because they feel like it's gonna attract a shark I don't know a surfer alive who doesn't pee in their wetsuit. But yes that's definitely something that I've heard, a lot. It'll liberate surfers everywhere, if we show it's cool to pee in your wet suit. And so after a bit more discussion Luke was on board for the first of our two experiments Well as a firm believer in the scientific method, we'll test it out And then you'll dive Well, depending on the results I dive If I can't pee, then the deal's off And so with that we started putting the four boards together We also started collecting scientific donations from the crew All right, so now it's time to fill these bags. Mm-hmm, what do you want to do first - pee or blood? Yeah, let's do pee. Okay, let's do rock-paper-scissors for who holds the bucket and who holds the bag Alright, one two three shoot? Ohh I gotta strategize... okay I know I know One two three shoot. Yeaaaa. Dammit Ohh that smells so bad It's urine Whosever's it is, they need to hydrate - dude this is going to be a nightmare. Oh it's warm Your pouring sucks! Okay Oh that smell of All in the name of science That's a great time of day to be doing this cuz we have a lot of sharks looking down here we got three or four lemons on the surface and I can actually see two Tigers down on the bottom and that's actually a massive tiger shark That is huge All right, see if you can do it better job pouring than I did. Oh my gosh Oh wow. There's a feeding frenzy It's fine What do you mean don't move it? I almost lost my hands They're not gonna jump out of the water. Okay, so we've got sea water as our control, fish oil, we have urine, and cows blood So while Luke is bravely swimming the four surfboards out and anchoring them in place in preparation for the one hour countdown Now is a perfect time to explain the cool tech on each board I designed and built from scratch with my buddy Shawn Hodgins For this experiment to be robust All four boards need to start pumping at the exact same time after Luke has them in place That means we need to somehow start the pumps using a radio signal from the boat so each surfboard has a waterproof receiver box like this that also hosts the battery, a custom printed circuit board, and two Arduinos Then I have the remote control and as soon as I hit this button They all start pumping at the same time We know each pump is working because the corresponding yellow light is lit up That's important because they're too far away from the boat to see if they're functioning properly To pump the blood and pee We're using a peristaltic pump this is a perfect choice because it's a totally sterile way to get the blood from the bag to the Ocean since the blood never touches any sort of valve or something It just has these rollers that sort of pinch and push the blood through the tubing in a manner that just happens to be similar To a severed artery And so with the board's in place It was go time operation shark bait test thing commence - three two one... beep All four going we have confirmation Everything is rolling. The experiment is underway. We'll, let them go for an hour just dripping stuff out And yea we'll see what happens. And after ten minutes I was really surprised there wasn't a lot of action on any of the boards So so far. It's pretty interesting I mean we've shown if you have a massive cut and you're bleeding out and there's this many sharks within like 50 yards of you that they're kind of like 'meh' so like already that's an interesting finding, right? You would think like a little bit of blood and there would just be a massive swarm But that's not the case so far And to be clear we weren't dealing with small quantities here the human body contains five liters of blood and after you use Two liters, which is the exact amount. We're putting in the water then you die About 20 minutes in things were still pretty quiet, especially at the fish oil urine and control boards But then the blood board started attracting some smaller fish and soon after one or two sharks started taking notice Not a lot of love for my pee. I don't know why I find that kind of offensive, but I'm just a little hurt Eventually with about 15 minutes left things started getting pretty wild over by the blood board The blood was spread out and made almost like a blood run way So you have the surreal line of sharks swimming up this Enticing blood trail one after another only to be super disappointed to find a big piece of styrofoam We're almost done Three-two-one, the motors have stopped our experiment is done. I just like to point out the bags have been sucked dry So the engineering part of this experiment was flawless Gunshot everywhere. Yeah, no to super pissed off targets and so now it's time to go in and review the footage and get a final tally for each board and what we found was that four sharks went to check out the fish oil then zero sharks went to check out both the control and The urine and then the blood board had a direct visit from a whopping 41 sharks and so now that we debunked some surfing myths about Urine and proved that sharks certainly had a strong preference for blood over anything we tested the real question was Just how much blood is interesting to them and there was one part of the experimental design That was really nagging at me. Cuz that was cows blood right that was cows blood. You wanna try human At least 10 living braiding blood bags around here Not everyone was luke and I about this idea Yeah, and then just draw will just have fresh blood just mainline it and put it in the water one up. Would you be down? Moondog, what do you reckon look at me? So Luke made some calls and soon enough we had an amazing certified bhajami and phlebotomist on board And after some generosity from the camera crew and even captain Scotty We had four bulging bags of human blood for our second experiment This is my actual blood free to see if sharks have a taste for it And if they do I probably won't go three dining with them for the second experiment. We had three boards again We placed the control in the middle the board over here would pump the human blood Slowly at one drop a minute and then on the other side this board would pump the blood fast on average one drop every four seconds we were able to do that because another cool feature for the boxes we built was that by turning This knob you can control the flow rate So over time they can pump out different amounts and because sometimes we all have to step up and just do our part while Luke Once again risked his life by placing the three boards. I'd prepared to push a button All right, all of them are popular and good to go now the clock is ticking So we have like fifty five more minutes to go We'll see if the Sharks notice there One drop of human blood every four seconds may sound like a lot and it certainly is but it's also important to note That's 40 times less than the first experiment where we saw so much activity in this case halfway in to experiment number two Even though there were tons of sharks still in the area. The boards themselves were pretty quiet We'll have to see when we look at the footage afterwards. But so far it looks like the answer's no Five four three two one Experiments over and so after the full hour we brought in the board's and once again reviewed the footage to see that over the course of an hour zero sharks two checked out the control board zero checked out the slow blood pumpi...
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