all right everybody sorry about that little delay i'm back i had to readjust my camera so it was set up the right way i hope everybody can join us again hi everyone i'm angie and i'm an interpreter for california state parks and today is mpa monday as every monday has been for many many months now we're really excited to have you here joining us for our virtual programs and today we're doing a really fun experiment that is about sharks last week was actually shark week so maybe some of you have been learning all about sharks it actually ended yesterday but i figured why not we can keep it going for one more day to talk about sharks so we will be talking about elasma breaks today which are a subclass of the class chendrickthys which makes up um our cartilaginous fishes so our sharks our skates and our rays and we're going to talk today about an adaptation that um helps these animals stay buoyant in the ocean so if anybody out there is a scuba diver or a free diver you know a little bit about buoyancy and ways that we can compensate or change our level of buoyancy in the water whether that's with a wetsuit or a weight belt or a buoyancy compensator basically your your scuba vest and the animals that live in the ocean and swim around also need a method for controlling their buoyancy because they have a lot of pressure that is pressing down on their bodies all the time basically all the water that is between them and the surface of the ocean so most fish like this fish right here are rockfish have what's called a swim bladder and their swim bladder is similar to the lungs that we have as human beings everybody go ahead and take a nice deep breath you can feel your lungs expand and contract as you bring air into um that cavity in your body so the swim bladder in most fish is what helps them to stay buoyant right similar to our lungs um but our elasmobranks or our kendrick these or our sharks don't have a swim bladder so how do they stay neutrally buoyant or negatively buoyant enough to stay on the bottom of the ocean and swim around all the time so like i mentioned our fish have a swim bladder similar to our lungs if you've ever been fishing for rock fish before maybe inside or outside of a marine protected area then you might have noticed if you brought them up from a really deep part of the ocean that their swim bladder can actually be distended their eyes get really like popped out kind of creepy looking and their swim bladder can actually come out of their mouth because that um air that they have in their swim bladder basically expands as the pressure is reduced so the shallower you get in the water the less pressure there is and pressure and volume have this inverse relationship because of this thing called boyle's law uh getting into some physics for you guys but of course uh like i mentioned our kendrick these or our cartilaginous fishes don't have that swim bladder so how do they stay buoyant so we're going to do an experiment today but first i'll tell you a little bit about the thing that helps them to stay buoyant in the ocean which is called uh well i actually don't know if it has a specific name but it's basically a big oily liver so they have this organ specifically their liver that's filled with a lot of oil now oil um generally has a lower density than water and so therefore helps to keep our condrickies or our cartilaginous fishes nice and buoyant in the water so they can swim around if you know much about sharks or maybe you learned this week during shark week sharks actually have to consistently be swimming in order to survive they have to have that constant flow of water over their lungs in order to breathe whereas our fishes don't always have to do that so little difference between our our bony fishes and our cartilaginous fishes so again they have a really oily liver that helps them stay afloat so i went ahead and created two sharks for us here um made these out of toilet paper you can do this experiment at home if you want to test it out and on the bottom i've attached three pennies on each and this is basically going to represent the weight of the animal essentially the weight of this animal is what helps them get down to the bottom of the ocean but of course we're talking about what helps them a little bit higher in the water column so they can swim around and stay alive and continue to breathe so here i have a tub of water to represent the ocean and we're going to go ahead and put our sharks in the water okay so the first shark is going to have an empty cavity they're not going to have that oily liver uh they also aren't going to have their swim bladder because they're not a bony fish so this is sort of our test animal here and this cartilaginous fish or this shark is going to have this bag of oil inside of their body cavity to represent their oily liver so i'm going to go ahead and shove this inside see if it'll fit now uh you might be thinking wow that's a lot of oil and actually this let me get some of the air out of here so we can have a very accurate experiment um their oily liver can actually take up 90 of their body cavity that's a lot of the space in their body so if you're thinking that's a lot of oil that might actually be a pretty accurate representation of how much uh space their liver takes up and it can also account for about 25 of their body weight so it's really a huge adaptation a physical adaptation that they have so we have our shark with no oily liver and then we have our shark with our oily liver here and i'm gonna go ahead and drop them both in the water and we're gonna see which one floats now everybody take a moment to take a guess of what's going to happen to our uh kendrick these or our cartilaginous fish also known as a shark uh that's put in the water versus the one that doesn't have the oily liver what do you think's gonna happen let's find out so again uh this side right here my left side your right side probably or yeah i'm not sure how it's showing up on your screen um oily liver no oily liver here we go all right how fascinating so our shark right here with no oily liver just sank right to the bottom and our shark with our oily liver is floating pretty positively buoyantly buoyant on the surface um so this shows us that that oil in their body helps them to stay buoyant in the water so that they can consistently swim around and aren't constantly sinking to the bottom so another fun fact is that the oil in their liver is called squalene or contains a compound called squalene and they can also rely on it when there's a lack of food or a scarcity of food and they can actually kind of use up some of the nutrients in that oil to help them survive in times of food scarcity so i hope you learned something about sharks or elasma brinks the subclass of kendrick these are cartilage cartilaginous fish sharks skates and rays and now you know how they stay buoyant in the ocean and swim around if you have any questions go ahead and post them in the comments section thanks everybody for tuning in for those of you that don't know we do these programs every day at three o'clock and we cover various topics that are related to our north coast state parks in the time of covid19 we think it's really important that all of us stay connected one way or the other so whether you're able to make it to our parks or not we're really glad that you're here with us online and continue to engage if you enjoyed this video go ahead and like share and comment and i'll answer any questions that you might have we'll talk more about sharks and more about marine animals uh in the coming weeks one thing i also wanted to mention about sharks i have this poster behind me and it represents the animals that are likely to benefit from marine protected areas we have 124 mpas in california and there are lots of different animals that benefit from their presence and some sharks benefit from them in general our larger sharks that are highly migratory um aren't directly benefiting from mpas but they do indirectly benefit from the abundance of life that exists in our mpas so if you're curious about that this poster is available online i'll post the link for it there's a really fun coloring sheet for it too all right catch you next week thanks everybody for tuning in bye