We speak with justin cordova about the elusive deep water sharks.
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Justin cordova
Co-founder of The Rogue Shark Lab
Deep-water shark taxonomy
I'm joined by Justin Cordova who I met at the Indo-Pacific fish conference and who then came over to work with some of the sharks in the museum. We got on well and I was just seduced by his infectious positivity and love of what he does. So thanks so much for coming on Justin!
Thank you so much for having me Thom. I'm absolutely happy to be here.
Do you want to give us the backstory on how you ended up specialising in deep-sea sharks? And the other hats you wear to be able to do that?
A question I get is always: so why are you doing this? What got you into sharks? Honestly, it's just been one of those weird infectious things that happened to me before I probably could develop memory. I guess I was just a child and my parents would tell me ‘you were in the Baltimore aquarium and we took you to the shark section and you would just cry when we took you out’. So they knew there was this weird emotional tie to just wanting to look at sharks as a child. Now I just tell people that I just grew up and never grew out of it. Going through school, I just managed to talk to some science teachers that I was more or less close with, and they had mentioned up the street in Moss Landing there was a Marine Lab there and there was a professor that was working on sharks. And that was Dr David Ebert. And so I looked around and by some kind of weird strike of luck, the university had an amazing program that was called UROC (Undergraduate Research Opportunities Center).
It was like a mentorship thing wasn't it?
Exactly. And I just got very lucky and I initially worked with invertebrates. I remember hearing someone saying something along the lines of: ‘Those sharks are stinking up the area’. And in my mind, I was just like: ‘Sharks? I’m in!’ And it was all deep-sea sharks. It became like a new shark renaissance in my mind on defining ‘what sharks are’ and ‘what they look like’. But it was a project that Gavin Naylor got the NSF Grant to do and it was part of a shark tree life project that he did. I was kind of waiting to see who would claim these sharks and sure enough, my to-be mentor Paul Clerkin came out and he started getting these body bags out. I was just like I'm very interested in helping you out, and it started out like that. From there I got exposed to all sorts of deep sea sharks.
When I started the graduate program, I decided to do my work on this really obscure group of deep sea sharks called demon cat sharks. Initially I wanted to learn what skin patterns or textures can differentiate either groups or species within the genus Apristurus.
“...it was all deep-sea sharks. It became like a new shark renaissance in my mind on defining ‘what sharks are’ and ‘what they look like’.”
Because we hadn't really resolved this group, it was sort of a fuzzy cloud of slightly different sharks. it's one of the groups that people avoid because it's so difficult.
Exactly! It was a large task to take on, but I loved it. And the thing that I loved about it the most is that no one really knows or cares that much about it. You know, everyone wants to work with great white sharks and learn the different times that they feed or they want to know any and all minuscule detail about it. And I just described a new species of demon cat shark from the Indian Ocean in 2021!
so we're still figuring out new species and their life history. we're still on the Discovery phase!
Exactly. We haven't started experimenting, we're still like ‘Whoa this is new!’. So, after I graduated I managed to find a job as a Fisheries Observer and it's kind of like being a fish auditor. I take into account all the fish being caught in commercial fisheries. I'm so thankful for my job now and every once in a while my job's just like ‘hey, they're fishing out here, do you want to audit the fish that they catch?’ And it's so funny because I get so excited over the deep sea sharks when they're caught as bycatch. They want to toss them over immediately and I'm just like giddy and I'm just like ‘Oh, that's that kind of shark!’ They're like: ‘Yeah, okay? Get get it overboard’. It hasn't been seen since the 1950s! It's just so amazing.
With that being said, I was just remembering when I got back and I started getting my work underway and making sure I can like make a living and everything like that. I ended up rooming with an old labmate of mine, Vicky Vasquez and she had word that there was a museum collection that was being downsized, and that there were deep sea sharks in there. So Vicky said no we need to keep them. So we kind of just stored them in our garage basically. Fast forward, she managed to establish a nonprofit so we were able to either put the expenses under the nonprofit to at least have them in ethanol, or something to just like keep them from drying out. And then it kind of evolved into having more of an educational and research combination, where we're trying to teach people about sharks. We want to try to do our own research as well and it's been quite the adventure to say the least.
On top of your day job! So just to get it out there for the listeners this is The Rogue Shark Lab.
So should we dive in on some sharks! Let's talk about the critters! So, how are the shallow and deep sharks different?
So, that's a pretty interesting one and I always kind of struggle with this one too because there’s not one way to define a deep sea shark. You can’t also go by depth ranges because whilst they inhabit below the 200 meter range, you have some shallow water sharks like Angel sharks that can go down there too.
And great whites go down to 1000m…
Exactly. Plenty of them visit the deep sea. Even here in San Francisco Bay, we'll have like seven-gill sharks come up into the shallow waters. But, I think there are some general things you can look for to distinguish that it's a deep sea shark. So you'll have the eye colour, for example. These are broad examples, but I would say if I were to see that iridescent green/bluish/emerald kind of colour, its a deep sea shark.
And it fades very quickly after death, so it's quite a lucky few who've seen that weird glow.
Oh yeah.
But there's an eerie green almost radioactive glow from a lot of the deep sea sharks and that's to do with their vision isn't it? It's the same as cat’s eyes. It's a reflective membrane at the back of the retina, so even if a photon manages to get through the retina and not hit any of the light receptors, it gets a second chance as it’s bounced back. It's really good at working in low-light but it does mean that as that light bounces back and you see it, there's like a light coming from inside the shark.
Yeah, really creepy. I always think of it as just like when you put a light through like a gemstone or something. But it's so eerie because it's so smooth. I think one of the the more interesting ones I saw recently was my first fresh lantern shark being caught off of Japan. And I just remember seeing this hue of purple on the skin. And I've seen so many Lantern sharks where they just turn black. But to see this purple colour coming out of this shark, it’s like ‘Wow, I have never seen that.’
But going on from that, any shark that glows in the dark, that has some bioluminescence, is also likely a deep sea species.
And lantern sharks are currently holding the record for the largest bioluminescent vertebrate aren't they?
Yeah, one of my favourite ones too that glow in the dark are the cookie-cutter sharks. I know that at least in one of the species, they have their ventral side (the underside) having the bioluminescence but they have a weird interruption on it, like a dog collar. I suspect that that's supposed to be tricking a predatory fish into thinking that it's a very tiny fish. I think I've only seen one of them in my life and it's just so unique seeing how big these things are. I've been to fish markets around the world and I've seen like these tuna or dolphin fish, and they'll have like these little chunks missing out of them.
and you see it on gear as well, they sometimes go for the gliders. once you can see it, you can't unsee it. it's this perfect little excavation. and that horrible lower tooth rack that does this, it's all one fused tooth. so when it sheds it, it sheds it like a pair of Dentures… it sheds the whole thing.
A cookie-cutter shark with the infamous fused lower teeth. Image courtesy of Jennifer Strotman
Exactly.
They've got really weird teeth. I got to dissect one recently, And there was a fairly recent plug of tissue inside it. it had obviously just fed before it was caught or maybe even fed in the net. And it was interesting to see what it looks like from the shark end, ‘cause of course, we see the perfect cookie cut, but this was a spiral. So we could we could roll it up like a fruit roll up and make the plug. But actually, it was an unfurled strip of flesh. It was really interesting because the thought is that they suck on with those lips and then do a a barrel roll essentially.
Yeah exactly just like a clean plug out. So this would suggest that it kind of spirals in and then pulls out?
yeah so the tissue wasn't a plug, I was quite surprised. I could roll it up and make it look like the plug, but it was more like one of those fruit rollups. it was a strip. I bet other people have noticed that, but I wasn't aware of that until I went exploring in this shark.
That's so cool!
So other unique ways that deep sea sharks have been able to adapt to new and extreme environments is when you see sharks with more than five gills, more than likely that's a deep sea shark. It helps them collect oxygen in these low oxygenated areas.
can we do frilled sharks because i’ve recently become obsessed with them
Yeah, I always like seeing them and it's always so funny because they have such a weird primitive form to them.
Frilled shark. Image courtesy of Citron.
they look like a lizard, they don't look like a shark.
Yeah, like this big weird lizard eel thing that is very long and has like one dorsal fin. The reason why they have the name ‘frilled’ is because of the gill filaments, they come out as a frill. They just have this really unique visual to them and what sticks out to me is their teeth. You don't see that kind of tricuspid look on many sharks at all.
so the teeth are arranged in rows. and you'll know that sharks replace their teeth on this conveyor belt, but these guys have… it's like pads isn't it? it's like Stripes of teeth! and they eat squid don’t they? is that the thought, that these teeth are quite good at getting a hold of a wriggling squid?
Yeah, squid… I've also seen other soft-bodied animals like that too.
yeah they have this lizard body plan, this long Serpentine body. they are one of nature prototypes they're amazing
Yeah I've only seen one in a museum collection and this specimen was from South Africa. I mean these things are pretty big very long-bodied animals, so that's where the lizard body plan kind of comes in.
I always hold on to them even if we don't have enough data to make it part of the collection because it's just amazing fodder for public speaking. the kids love these things-it's a proper sea monster!
That reminds me when I was talking with Dr Sato and he was like ‘Can I tell you a secret?’ and I was like ‘Yeah sure.’ He was like ‘I still like deep sea sharks’. And I'm like… why is that a secret?
‘I'm not bored’ I like that.
I continue to like them because I always tend to find something new. You know, great white sharks? Sure. Lemon sharks? Sure. I'm pretty sure there's lots of information on it and we could go into all the nuances of how these animals operate and everything. But what gets me is these unsung heroes which is the deep sea sharks. I got so into dermal denticles because you know deep sea sharks have an array of different ones. Something like a bramble shark has like these rose-thorn dermal denticles. I've seen a video of someone just rubbing their hand on it barehanded and then just you see the lacerations on the guy's hand and I'm just like: I don't know why you just did that.
and yet if you rub it the other way it's fine because they're hooked like rose thorns. but you're right, there's magic to these structures because there's so much detail in them. and just break the word down, ‘dermal denticles’ literally means ‘skin teeth’.
Exactly, and with deep-sea sharks, one thing that I don't see too much is when you look at something like a Mako shark or a thresher shark, their dermal denticles tend to be less overlaped- more tight. They almost look like scale plates, you know like on a fish. And I don't think I've seen a pattern like that on any deep sea shark.
they're probably moving at much faster speeds, so you get that laminar flow. whereas a lot of the deep sea ones are are quite slow moving.
Exactly yeah. And even their bodies feel a bit different. I don't know if you have, but I've had to throw these sharks overboard and I can definitely tell the difference in muscle structures.
they're bag full of fluid. I can feel the spine but…
Like a bag of organs!
they are just ‘loose’. and I don't know if that's the oil getting less viscous at atmospheric pressure, or if they're just like that down there. but they are just loose…
Totally. And that's almost the same thing for teleosts, you know? A lot of them are really soft, I think that's more with like pressure but also maybe with the no need to swim very fast.
yeah it's multifaceted, it's like an energy saving thing, you're supported by the water, you're not having that burst speed so you don't need a rigid body that these muscles can push off. but yeah I think that's a nice little thing to put when you're pushing back on the idea of the deep sea. and that the idea of these animals are all sort of spiky and horrible looking, is that actually lots of stuff is soft. the deep sea is very huggable.
can we bounce around a few of the other famous deep sharks? we've got to do the goblin shark because I usually push back with like ‘oh no the deep sea creatures aren't that horrible’. but this one… no this one creeps me out. this one isn't good.
No goblin sharks are amazing! They're in the same group as great whites, makos and thresher sharks. Let's start with how they look.
yeah the the obvious origin of the name. they've got one little party trick that stands out once you see it…
Exactly! They have the fastest jaws out there on this side of Mississippi. They can protrude their jaw so fast and they project their mouth, make an opening in their mouth cavity and it can make like a vacuum. So it kind of also sucks in small fish.
A goblin shark. Image courtesy of Dianne Bray / Museum Victoria.
yeah the jaw comes out to you, but also the water is pulled into that jaw and you just go into the mouth
That's pretty much how it works. I believe that their nose actually helps them detect fish as well, so it kind of works almost in tandem, kind of like a metal detector.
yeah the trigger is this point along the snout, like it's a measuring stick. once you're in range, the extrudable Jaws come out.
The name comes from… I believe it's a Japanese word: Tenguzame. ‘Zame’ is ‘shark’ and ‘Tengu’ I believe, is ‘Goblin’.
oh, that's cool!
Right, I think one of my favourite deep-sea sharks that I feel never really gets talked about anywhere, but is a quintessential deep sea shark is a viper dog fish. When I first saw it I thought about one of my favourite scifi movies: Alien.
Yes because it's black too! they look almost iridescent, almost metallic. Plus the teeth!
Yeah the profile of the head is the right shape, they have that protruding jaw-thing and I was just like… oh man I really like this one.
there's one character amongst the deep sea sharks that is mysterious. I feel like I don't know much about it, and it pops up decades apart, and that's the megamouth. we just don't know a great deal about it. that weird huge mouth… the tiny eyes… these little filament teeth. there's hardly any specimens of them.
I feel like recently, more of them have been showing up. It was almost like the coelacanth, these are ‘living fossils you'll never find many of them’. I think at first, it was always a big event, it was always a news thing. A lot of people think that they just travel a lot on the water column, during the night time. I think what might be happening is, we're just not seeing them. Because they predominantly prefer just really deep waters where we don't fish as much.
well one of the things we we do know about them is they're incredibly long lived. they top a couple of hundred years right? the record holder is currently the Greenland shark I think? it’s the oldest vertebrate.
Yes but there’s a lot of issues with estimating how long does a deep sea shark live, because historically speaking, we take the vertebrae and then like the rings of a tree count how many rings are in the cross-section.
but that assumes seasonality, which the deep sea might be disconnected with. one of those growth rings might just be a good whale-fall, a good chance to put on some meat.
Exactly.
So, we have touched upon this in the past but how often do you get asked about Megalodon?
Oh, not often anymore but I do remember that fateful day when I saw that documentary… I remember thinking to myself… what are they doing?
“ I do remember that fateful day when I saw that documentary… I remember thinking to myself... what are they doing?”
it was so irresponsible. you can be a responsible factual Channel and then just for the sake of ratings and to pretend you don't know what you're doing is irresponsible.
I do get that question asked maybe once or twice a year, and I do try to be as sympathetic as I can because I always think: what proof do you think there is? Have you seen like anything with missing chunks in them?
it's about what we want to be true. it's always revealed when you ask the follow-up questions. plus, even when it was around it was a shallow-water shark, it was never hiding deep!
Right?!
yeah so actually it's about you wanting to tell a spooky story about there being a big shark that we don't know about. theres no evidence that this thing is hanging around.
Right I feel like it's a very hard thing to hide.
don't even entertain it because the whole premise of the question is: ‘wouldn't it be cool if…’ and that's not how you go about getting data.
Yeah, exactly. Of course it would be cool but until then… I don't know what to tell you. Like, sure if you ever find one let me know! We'll be famous scientists together… I'll be the first one to say I knew they were real.
But, I think at first that question used to always bug me. Now I'm more coming out of curiosity.
I'm happy if anyone shows an interest, as long as they'll listen to the response rather than get frustrated that it's not a ‘yes’.
thank you so much for for coming on and having a chat with us!
Oh thank you Thom, I had quite a blast!