Most of my time with bioacoustics, thus far, has been with playing sounds – my master’s work with an active acoustic tag – or with identifying odontocete, or toothed whale species, in glider data (typically known as high- or mid-frequency vocalizations).
For my PhD, I’ll be expanding what I know about whale acoustics and looking at baleen whales from glider and float data as well. I started into this the last few weeks and it has been fun, but definitely feels like a step back in time trying to look up literature and see what exactly I am hearing in the data – I’m not used to working with low-frequency sounds.
Low-frequency sounds
What do I mean with low- vs high-frequency sounds? These labels are based on human hearing (of course). Humans (babies!) can typically hear from 20 Hz (hertz) to 20 kHz (kilohertz…hertz*1000; 20 kHz = 20,000 Hz). As we get older we start to lose hearing on the higher end. But marine mammals vocalize both below and above our hearing range. The low/high delineation is “generally” accepted at 1 kHz, and typically baleen whales vocalize below this, and toothed whales vocalized above this. But remember, this is just USUALLY. There are always special cases that don’t follow the trend, and its all relative terms when calling things low and high.
This figure from Mellinger et al. 2007 is a great way of see where certain species typically vocalize. (Click he figure to link to the PDF of the paper and zoom in)
Looking at sounds
So since some whales make sounds below my hearing range, and some make sounds above, how do I hear them for analysis? Well first of usually I am identifying sounds by looking at them, at a spectrogram (we’ve posted those before right?).
Then sometimes I need to listen AND look to identify what the sound is, or gather more info about it. Wonderfully there is a work around. For really LOW sounds, you can play them faster, and then that increases the perceived frequency, so you can hear it. Vice versa, for really HIGH sounds, you can play them at half speed, which changes the perceived frequency, and then you can hear them. Does anyone remember Yakbaks? Speeding up your voice makes you sound like a chipmunk, slowing it down makes you sound like…a whale?
This summer I spent a long time underwater. Not only for work, not just for fun. For debriefing and peace of mind. The last couple of months, swimming has been my way of being with myself and thinking freely about life, cheese, and sperm whales. While performing long dives down to a few meters of depth, I have been thinking about the sperm whales’ amazing ability to dive so deep and for so long.
Even though marine mammals breathe air, just like us, some species are able to keep their breath underwater for longer than two hours and others can go down to 3 Km deep!
How do they do it?
I do not do scuba diving anymore and I am happy that I do not have to tolerate the suffocating, funky smelling, and how-do-I-get–out-of-this wet-suit. I love keeping my eyes wide open where the seawater is clear enough to make the use of mask or goggles unnecessary. This way I feel like a natural part of the mysterious sea world. The indescribable sensation of flying underwater can only be compared with a couple other feelings. Nevertheless, I admit to struggle, like any other human, with a couple of issues.
*Not A Human
Pressure, oxygen and temperature limit my expanding politics while in this wet world.
You have certainly noticed that the deeper you go in the sea the higher the pressure. Specifically, the pressure by the water to any object is called hydrostatic and increases by 14.5 pounds per square inch (psi) (=1 atmosphere) every 10m you dive deeper. You can quickly feel this pressure in your eardrums once you are 3-4 meters deep. Can you even imagine the pressure down at 2000 m?! Let me help you. It is estimated that at that depth the weight of the water becomes as heavy as two baby elephants (~200Kg) balancing on a postage stamp. If you have ever seen the squished styrofoam cups that return from our visits to 1500m with submergence vehicles, now you know what happened to them. It wasn’t exactly an elephant that sat on them but close…
Results from hitchhiking on a CTD.
The decrease of water temperature as I dive down is also a limitation. Luckily, all the cheese consumption I have been persistently investing on has helped me create this fine layer of fat tissue that makes me unbeatable to the cool (Mediterranean) water temperatures for long periods. Fortunately for human life, my fatty layer is thin enough, but unfortunately insufficient for whale depths.
While I move deeper into the darkness of the ocean there are more obstacles to encounter. Despite my healthy lifestyle, I am in need of oxygen less than a minute after I submerge myself. My lungs can only store a certain amount of air (probably a bit less than 5 liters) dependent on my age, physical size (consequently my lung size), and my fitness state. Even though I exercise a lot, I do not smoke, and I am tall, still my lung capacity does not allow me to stay underwater for as long as I desire. Specifically, no more than about 40 seconds. My body requires fuels for my brain and internal organs during a dive to the abyss. Or even, down to 7 meters and back.
Well it is actually not that bad, if you think that we can keep our breath for longer underwater than on air pressure. While submerged in cold water, instinctively decreases our heart rate and metabolism for saving up oxygen. Marine mammals use the same trick. The best example is the Weddell seals; during their deep dives their heart rate decreases down to four beats/minute!
“Haven’t felt my heart for 15 sec. I am worried.”
Whales have managed to succeed on everything that I suck at (besides slack line).
First of all the fat. They have a thick layer of fatty tissue under their skin, called blubber. It functions as the best thermoisolating material. Keeps their body temperature from dropping dramatically when the environmental temperature falls under what they can tolerate. See, fat is good. Go on, have that piece of brie.
Sperm whales and beaked whales do not crack under great pressure, as humans literally, and often metaphorically, do. In contrast, they thrive where the conditions are unbearable for other whale species. They have adapted in the extreme conditions of the deep seas and that pays them off with food. It gives them access to the bathypelagic squid to fill their demanding bellies. It resembles an all-you can-eat buffet where you are the only client.
Any psychological boosting, power phrases, meditation, or confidence injections prove to be useless towards their achievements. What helps them instead, is primarily their flexibility. Their rib cage can fold in to avoid crushing from the high pressure. Both the rib cage and lungs collapse every time the animal dives 2 Km down and then recover when it comes back at the surface. If you thought your routine is tough, now you may reconsider.
It is easy to understand how that works by the following image.
Ouch
In practice though, the sperm whale in action does not show any indications of being collapsed at great depths. Its skin and the whole body look smooth and perfectly well shaped without any evident ruptures or deformations. Yeah, there is proof of that. A lucky NOAA group incidentally captured a sperm whale on camera while sampling with an ROV (Remotely Operated Vehicle) at 600m depth. Check their reactions, surprised indeed.
These deep divers are known to remove the 90% of air from their body, by exhaling it before the dive, to be easier to simply sink down, dealing this way with buoyancy issues. Footage has proven that some marine mammals hardly move while they sink. They gently slide into the water, heads down, without even moving a muscle. You can imagine how much oxygen the muscles would require to move that giant tail…
For the same conserving purpose, marine mammals choose to “unplug” some of their internal organs and functions that are not vital during their long journey to the sea bottom. Who needs digestion, liver and kidneys while hunting…?!
However, they still need oxygen while down deep. They need to move around for chasing that yummy squid and their muscles require oxygen for that. Their well-hidden secret lays in their blood; they have what I call the super blood. They have a higher percentage of red blood cells where oxygen is stored, and a higher blood to body volume ratio that gives them extra storage. On top of that, there is the myoglobin. Ta-ta!
One unusual word for human, a tremendous offer for beaked whales!
Myoglobin, such a mouth filling word, is a protein in the animals’ muscles that stores oxygen and is responsible for making active muscles look red and sometimes even black. For the diving animals, myoglobin is 10 times more concentrated than in human. Too much of this protein could cause health implications to people mainly because of low viscosity, causing clogging and sticking together. A recent scientific discovery showed that in beaked whales, this crazy amount of myoglobin is functioning because it is positively charged. According to the laws of attraction (opposites attract and likes repel) the myoglobin particles manage to keep from sticking with each other and any circulation clogging is avoided.
I would be happy to announce that the sperm whales are the Kings of the Abyss. Yeah, that would give me immense satisfaction. However, beaked whales beat them to that. They get down to almost 3000 meters, about 1000m deeper than the Kings of my Heart do. They win, not only more of that elusive squid, and our admiration, but also the highest levels of myoglobin.
At these great depths, where any kind of light can only be bioluminescence produced by fish or other invertebrates, the sperm and beaked whales use their spectacular biosonars to “see”, making the deep oceans into Operas of Clicks. They are the Divas of the Deep for a reason.
If you want to learn 80 sec more about underwater fireworks (bioluminescence) don’t miss this video.
To return where I started from, I am going to take you for a swim. Not just a usual swim in the clear, turquoise, crystal calm, and safe Aegean Sea. We are going night swimming. The whole sea is dark and the whales cannot even see their own tails; we struggle to see if any swimming suits are on. The water is dark as the night. A starry night. Swimming at a beach on the western part of the island of Lesvos (home of the Department of Marine Sciences of the University of the Aegean), we feel like Divas while playing with the underwater stars. Every little movement causes the water to sparkle, and produces hundreds of tiny shiny tails just like shooting stars. Little planktonic organisms almost invisible to bare eye, produce bioluminescence when excited and make our experience exciting. Truly magical!
Soundbites is a weekly (biweekly, mostly) feature of the coolest, newest bioacoustics, soundscape, and acoustic research, in bite-size form. Plus other cool stuff having to do with sound.
Bioacoustics helps find what may be a new beaked whale species: this one was hard to miss this week, as it was all over the pop press news as well. Here’s the original article. Passive acoustic monitoring in the Antarctic found echolocation and communication signals that were beaked-whale-esque, but unlike species seen before this. It might be a new species!
Cicadas and birds partition acoustic space in the tropics: I think the acoustic niche hypothesis is really neat, and it’s cool to see it in practice. Bird species and cicadas in the tropics vocalize at similar frequencies, so birds avoided calling when cicadas were calling. If they did call during cicada song, birds changed their frequency to avoid overlap.
Fun link of the week: Michelle had an awesome post last week about paleo-bioacoustics (what a field name!), so continuing in that theme, let’s talk about terror birds. Have you guys seen a terror bird skull before? Terrifying. This new research suggests that they had low voices and were better at perceiving low-frequency sounds. This means we’re one step closer to my dream, knowing what dinosaurs actually sounded like…
In the midst of the summer and early fall when I was traveling a bunch and doing field work, I remember thinking how nice the term would be to be in one place for a while and get some analysis/other work done. What I didn’t realize was how unexciting my life would be for blog posts….
I guess excitement depends on your interests, though, because for me there have been SOME exciting moments standing in front of my computer. I’ve spent the last month putting my master’s on hold, instead analyzing acoustic data collected from one of our gliders that was deployed back in March, and then deploying and analyzing another glider all within the month of October. Want to see what I found? Good. I was going to put in the images anyway.
Here’s a Stejneger’s beaked whale click. The top image is a long term spectrogram, or LTSA, that shows 15 minutes. All the little bits around 50 kHz are beaked whale clicks. The middle spectrogram just shows one click during a fraction of a second, and the bottom shows the wave form, or the amplitude of the click.
From the March deployment, the excitement came in the form of TONS of beaked whales. Like so many. Like all the time. Including the super weird looking Stejneger’s beaked whale (Mesoplodon stejnegeri). I can tell the species by what frequency the click is at, how much time there is between clicks (inter click interval, aka ICI fyi), and the duration of the click. They are all unique features for this species of beaked whale, which I know thanks to other people confirming that by combining visual and acoustic data like was done by theses lovely folks at Scripps.
Here’s two porpoise species detected together – harbor porpoise (the two higher frequency red specs) and Dall’s porpoise (the middle, slightly lower frequency). All together a bunch of those clicks make up that light blue section in the LTSA on the top.
The March deployment also brought excitement through porpoise recordings! Did I mention that glider was the first of its kind to record ultra high frequencies? We used a 394 kHz sampling rate, which means we could detect vocalizations up to 196 kHz, which is where porpoise and a few other odontocetes (toothed whales) vocalize. Most equipment doesn’t sample that high (memory gets filled too fast) so this was pretty neat-o. I’m a big fan of looking for these ultra high frequency encounters because they are so obvious in the upper part of the LTSA, far above the background noise.
And like I mentioned, I did go out in the field one day. We deployed one of our new gliders for a few days just outside of Newport in early October, and I went out on the recovery. I took this one super exciting picture of these gulls on the back of the ship. You’re welcome.
Piper helped Holger and Alex prep Will the glider before he got deployed in early October.These gulls agree with “no excitement November”. Until I threw pistachio shells over the side. Sadly this is the only picture I took of the whole glider recovery.
