As promised, more of the Johnson Sea Link

When we were on the Abrolhos research cruise aboard the HBOI/CEPEMAR ship Seward Johnson recently, I posted a little clip of the outside of the sub.  In that post I promised better quality and longer clips when I got back to land.  So here, (in HD goodness if you want it) is long-time pilot Don Liberatore giving a neat history of the Johnson Sea Link 2 submersible.  What I find most interesting is his comment about how he got into being a sub pilot in the first place: sitting on the dock in the 70’s he and some buddies saw the HBOI ship pull into port with the original JSL1 or Clelia (not sure which) on the deck and he thought “how cool is that?”.  This comment is exactly what I meant in my recent post about the importance of Human Occupied Vehicles (HOVs), or submersibles, for inspiring people to careers in marine science.

The 500pixel column width here on the blog is a bit limiting; if you want to see it in HD, roll over to the YouTube channel and check it out

DTF's Christmas Research Redux

In this peri-celebratory season things will be a little quiet here due to other commitments, so I thought I would bring back a few of my favourite research posts from the year.  Since this blog was effectively launched early in 2010, you might not have seen some of the earlier ones.  So here they are, I hope you enjoy them:

What’s a manta do?  A discussion of the surprising discovery that one of the worlds largest ocean-dwelling species is not “one” after all, but “three” (species, that is)

Slow down = Mow down?  The most viewed post of the year on DeepTypeFlow (>30K hits); a discussion of Ed Gerstein’s research on hearing abilities of manatees and the implications for boating in Florida

Your calamari wants a flat screen. A startling discovery that octopus can see hi-def TV, but not regular TV.  Bloody techno-snobs…

The Ocean conveyor running AMOC.  Two contradictory studies show the complexity of the global climate system and the role that the ocean plays therein.

When can we stop sampling and have a beer?  (Predictably?) one of my favourite topics - species accumulation curves and what they tell us about biology and about how to sample it.

When errors detract from the message, who is to blame?  A cranky rant about an especially shoddy bit of scientific editing.

To see the world in a grain of sand: movement from a turtle hatchling’s perspective.  An exploration of work out of Daniel Goldman’s lab at Georgia Tech regarding the suprisingly versatile turtle hatchling

A new angle on diving in whale sharks

Recently I featured a piece about how turtle hatchlings change their movement strategy several times in just the first few hours of life in order to suit their changing needs as they move across different types of sand.  Well, to go from the sublime to the ridiculous (or rather, just from the really small to the truly gargantuan) there’s a new paper out that shows that whale sharks, too, adjust the way they move according to their needs.  This new work follows nicely after Phil Motta’s paper earlier this year, also discussed here, which took a comprehensive look at how whale sharks feed.  Between them they make big strides in the autecologyof whale sharks.  The new paper, by Adrian Gleiss and Rory Wilson from Swansea University and Brad Norman from ECOCEAN, describes work they did at Ningaloo reef in Western Australia, perhaps the world’s best studied aggregation area for whale sharks.  They took a new type of accelerometer tag developed in Rory’s lab called a “daily diary” and deployed them on wild whale sharks to measure not only where they are (like traditional wildlife satellite tags) but also details about what the animals were doing: the beating of their tails and the rientation of their bodies in 3 dimensions.  From this information they could basically reconstruct the animal’s actions with computer game-like accuracy (indeed, the software looks a lot like something for the X-Box!).  The findings show Whale shark with accelerometer tag. Photo: Steve Lindfieldan animal with a surprising diversity of movement modes and a sophisticated approach to minimising the amount of energy they spend moving through the ocean.  They also help explain one of the most enduring mysteries of whale shark biology - a curious pattern of super-deep dives over the abyssal depths.

The first big observation is that whale sharks have 4 different types of dives and that these probably serve different purposes.  It was well known from traditional tagging studies (sat tags record depth data as well as location) that whale sharks dive quite a lot throughout the day, but the new daily diary tags showed that not all dives are the same and, in fact, they could be easily discriminated as one of four main types based on what the depth profile looks like: yo-yo (probably searching), V (horizontal movement), U (feeding at depth), and bottom bouncing (searching at depth).

Four dive types in whale sharks. (a) yo-yo, (b) V-shaped, (c) bottom bounce, (d) U-shaped

The second and a really key finding is that all the dive types feature a gliding descent and an active ascent.  In other words, they don’t beat their tails on the way down, but they do on the way up. Gliding converts their negative buoyancy (a sort of potential energy) into horizontal and vertical movement (kinetic energy).  The fact that their dive has both vertical (depth) and horizontal (forward motion) components, without active use of the tail, shows that their bodies are adapted to convert sinking to swimming.  Most of that effect comes from their pectoral fins, which serve as wings for gliding, but there is probably a big contribution from that incredibly broad head, which serves as a sort of lifting canard, a flat plane that creates lift at the front end. Gliding is an extremely efficient way to move; not only are they not spending energy operating their musculature to beat the tail through the water to create thrust, but the drag coefficient of water across their skin is a third as much when they glide as when they are actively beating their tails.

The third finding, which Gleiss and friends really go into in some, ahem, depth, is that angle of descent and ascent is consistently different for each type of dive and that they are optimal for whatever the purpose is.  For example, a V dive is meant to cover a great horizontal distance, so the gliding descent is at a shallow angle and the ascent angle is the one that minimizes the amount of energy spent to gain horizontal distance. In contrast, the angles of a yo-yo dive minimize the amount of energy spent to gain vertical distance.  The important point is that for any given purpose there is an optimal angle - one that uses the least energy for the most benefit - for both descent and ascent components.  Whale sharks adapt the geometry of their dives to stay in that optimum zone and minimize the amount of energy they spend on whatever they are doing.  Clever right?  Well, its probably not a conscious decision, but rather a state of tremendous efficiency towards which they have evolved: natural selection is a powerful tutor.

Diving geomtry in whale sharks. The angles of descent and ascent (the two thetas) are optimised for minimum energy expenditureIn the course of their study, the researchers solved one of the great mysteries of whale shark biology: the extraordinary deep dives whale sharks do when they are over abyssal depths (see the Brunnschweiler reference).  These dives tend to happen around dawn and dusk and may exceed 1600m or more in depth; in fact, we don’t know just how far down they go, because most tags have a self-preservation device that cuts them free of the animal at 1600m, lest the tag be crushed by the immense pressure of the overlying water.  We’re talking depths enough to turn a Styrofoam coffee cup into a shrinky-dink thimble, as well as changing enzyme kinetics and making the urea in their blood greatly more toxic, so the motivation to dive so deep must be compelling. There had been suggestions that they go down to rid themselves of parasites (as a parasitologist, I never bought that: parasites would easily co-evolve to tolerate such a strategy), or to clean their filter plates (at those depths particulate organic matter redissolves!) or even to “sleep”, although there is no evidence that sharks do so.    Well, it turns out that they are dives of the V type, optimised to spend the least amount of energy while achieveing maximum horizontal movement (HD in the figure above).  In other words, to travel far, they glide deep, and then gently beat their tails and ascend at a very shallow angle (steeper angles costing more energy and achieving less horizontal distance).  This is a strategy best used during migratory phases when travelling, not feeding, is your number one priority. 

To recap then, whale sharks turn out to have at least 4 main types of dives, each serving a different purpose from feeding to horizontal travel, and the geometry of each type of dive is optimised to achieve the goal while minimising the energy cost.  Overall, it paints a picture of an animal that is a paragon of efficiency, which is understandable given that they dwell in the nutrient-poor surface waters of the tropics, which are typically much less productive than the rich cold temperate and Arctic seas frequented by their fellow filter feeders: basking sharks and baleen whales.  I suspect that future studies will show that whale sharks deploy these movement strategies to travel efficiently between hotspots of tropical productivity, be they fish spawning events or patches of seasonal tropical upwelling, and that they are therefore extremely strategic masters of the feeding/travelling trade-off.

Gleiss, A., Norman, B., & Wilson, R. (2010). Moved by that sinking feeling: variable diving geometry underlies movement strategies in whale sharks Functional EcologyDOI: 10.1111/j.1365-2435.2010.01801.x

Brunnschweiler, J., Baensch, H., Pierce, S., & Sims, D. (2009). Deep-diving behaviour of a whale shark during long-distance movement in the western Indian OceanJournal of Fish Biology, 74(3), 706-714 DOI: 10.1111/j.1095-8649.2008.02155.x

A photo post from field work in Mexico

Sorry things have been a bit quiet on the blog lately.  Our field work season has reached a crescendo, with several back-to-back trips to Mexico where I and others from Georgia Aquarium are studying whale sharks that aggregate annually in the coastal waters of the Yucatan, and thats left little time for writing.  To learn more about the whale shark project, go here.  Its been a real treat lately, with hundreds of sharks feeding in the area east of Isla Contoy and Isla Mujeres.  Between the boat work, which focuses on photo cataloguing and ecological sampling, and aerial surveys, which focus on counting and distribution, we’ve been gathering a ton of data that will help shed light on why these aggregations form, and how to better protect them in the future.  Rather than write about it, I figured I’d let the pictures do some talking.  Required legalese: all these images are copyright 2010 Alistair Dove/Georgia Aquarium and may not be reproduced without permission.

Flating mats of Sargassum are home to all sorts of things. These baby jacks were seeking shelter from me and caught a red reflection off my rashguardThis is what we came for: a whale shark feeding east of the Yucatan.Any port in a storm: this tiny 2 inch barracuda was hitching a ride with a moon jelly

Most filefish live on rocky and coral reefs, but this one was vigorously defending a little bit of SargassumIts hard not to feel like the whale sharks are checking you out sometimes

Georgia Aquarium senior aquarist Marj Awai wielding the 7D and housing: stills AND HD video *drool*People are the biggest threat to whale sharks. This male had a close encounter with a boat but luckily came away with only shallow scrapes. We see deeper cuts from propellers sometimes, and utmost caution is warranted when moving among the animals.The most common view of a whale shark. Even though they seem to swim effortlessly, keeping up with them is only possible for short distances. This is the last one we’ll see until next years field work season. Adios amigo!

Dancing with a Giant - the reprise

You might remember an earlier post about Dancing with a Giant, in which I was pretty emotional about an amazing swim I had just done with a whale shark in Mexico.  Well I can now share the video of that animal.  There’s a good bit at around 0:50 where you can see right into his mouth, and see the filter pads they use for sieving their planktonic food from the water. In this case, he’s filtering fish eggs, which you can’t see because they are too small and are also transparent; thats good for us though, because it gives us a nice clear view.  Without further ado then, here he is, MXA-181:

Hola de nuevo, México!

Headed back to Quintana Roo in light of a good weather forecast and a chance to finish some chemical ecology sampling we aimed to do last time but were denied due to weather and other concerns.  What’s chemical ecology?  Its the study of how animals interact with the chemicals in their environment and shape their behaviour accordingly.  In this case, we’re especially interested in what whale sharks can smell, what sort of “odor landscape” they live in, and how they exploit this to find food.

Unlike a lot of “big” marine scienctists that work off ships in the UNOLS fleet, we actually work from small boats close to the coast, so weather is a key factor.  Do me a favour and pray to whatever deity or natural force works for you, in order that we get some favourable conditions to finish this work so we can move on to other things, OK?  Me?  I’ll be praying to Chaac, the mayan rain god, not for rain, but for no rain.  More importantly, I’ll pray to the head honcho of all Mayan gods, who also happens to be the wind god - Kukulcan - for no wind.  I may as well pray to Joe Pesci, but it can’t hurt.

If you have to go, go big!

When you want to learn about the biology of a charismatic species, any species really, sometimes you end up learning about the grosser side of life too.  Thats kind of how I came to take this picture last week in Mexico, where I and several others from the team at Georgia Aquarium have been doing research on whale sharks lately (see several other blog posts heareabouts).  It was taken during an aerial survey we did from an altitude of 1,500 ft in a Cessna 206 and shows a whale shark that has just defecated.  Now, whale sharks tend to do everything on a giant scale, so perhaps we shouldn't be too surprised, but I estimate the animal to be between 8 and 11m (25-35ft) in length and so, based on that estimate, thats a cloud of poo behind him thats over 30ft in diameter!  Its unusual to see wild sharks in the act of pooping, but this group of animals was so numerous and feeding so heavily, that you could actually see several clouds like this at any given time.  Whats feeding heavily got to do with it?  Well, unlike mammals, which tend to have a relatively fixed gut passage time for food, a lot of cold-blooded critters can, well, sort of push it out the back end, simply by pushing more in the front end.

Far from being a trivial observation of one of life's less savoury moments, it could actually become a really important research opportunity if we can manage to catch some of that magical egesta in a container of some sort, for analysis back at the lab.   Scientists can do all sorts of stuff with poo, like looking for parasite eggs or other pathogens, sequencing the DNA of both the shark and its prey species, or comparing nutrient values of food (from plankton tows) and comparing them to values from faeces to work out how much nutrition they are gaining from their food.  Its a great way to learn a lot in a short time and do it in a totally non-invasive way.

Mostly though, its a cool photo to gross people out at parties...

Dancing with a Giant

A lot of people think science is soulless, sterile or austere in its objectivity; there’s a prevalent stereotype of the scientist as a lab nerd in a white coat, out of touch with the “real world” and with the more emotive aspects of life. That couldn’t be further from the truth, of course. Most scientists I know – me included - are motivated precisely by a profound wonder and amazement for the natural world around them; its usually why they get into science in the first place. When biologists go into the field, they often end up reconnecting with those feelings, established during their formative years, and end up resorting to a sort of childish state of pure joy over whatever biological phenomenon that they happen to be studying. I just had such an experience, one that was so extraordinary that it may well have changed the way I think about biology forever.

As part of the research program at Georgia Aquarium, we are in Mexico to study the biology of whale sharks, which gather annually in the coastal waters of Quintana Roo, from Isla Mujeres north and west to Isla Holbox. Its bliss just to be out on the water again (its been a while), admiring the everchanging seascape, marveling at the myriad forms of life that make their home in the ocean, and reminding yourself that the endless stream of doom and gloom news about “the environment” isn’t really the full picture. Flying fish skip from wave crest to wave crest, pursued by sinister-looking frigate birds that swoop in to grab them on the wing, while turtles lazily periscope their heads above the surface to spy on pods of spotted dolphins that race around as if there were somewhere important that they really needed to be.

In due time, we found our objective, a group of whale sharks feeding at the surface, attended by a flotilla of ecotourist boats. Each of our team had a chance to swim alongside these spectacular behemoths as they were cruising effortlessly among the boats and patches of food, at speeds that exhausted a mere human to match.  We also photographed many of them for an identification database.  Then we took some time to gather data on the physical and chemical properties of the water, during which the ecotour boats petered away, returning their cargo of tourists to their respective all-inclusives in time for lunch and leaving us with the whale sharks mostly to ourselves. They continued to feed, constantly inhaling bathtubs of plankton from the surface tension, their gills flapping loosely on the rejected water current like flags in a gentle breeze.

It was at this point that I got in the water a second time. Rafael, our captain and colleague from Project Domino, had put us on a large animal that was feeding below the surface in a more vertical pose than their normal surface “ram filtering” style. This more upright type of feeding, which they use when food is especially dense, sees their tail sink down towards the bottom and cease its rhythmic swinging and, hanging suspended like this, the animal begins to actively suck in enormous gulps of water. In this state I was able to approach the animal much more closely, a large male, and to see how each pulse of that fantastic mouth was pulling in not only water but tiny silver vortices of air down from the surface, such was the force of suction. He was suspended like this for what seemed like an eternity, but was realistically perhaps 15 or 20 minutes, during which he continued to feed and appeared completely indifferent to my presence. I was able to swim over every part of his massive frame and inspect every detail, from his tremendous girth to the creamy white belly distended with food, and from the remoras that pestered his every fin to the tiny copepod parasites grazing across his skin like herds of hoofstock might roam a savannah.  His body was home to a veritable community of hangers-on. I watched his eye roll carelessly over me while he continued to inhale vast amounts of water and plankton, all of which disappeared into that cavernous mouth with its 20 jet-black filtering pads. We continued to dance together like this – or rather I danced around him - close enough that I could have reached out to touch him at any point, until with a tiny shake of his head and a hefty sweep of his tail he was done with the meal and headed off in search of another patch to vacuum, leaving me breathless from a cocktail equal parts exertion and exhilaration.

Back on the boat I did my best to relay to the others what I had just experienced. Despite apparently talking “a mile a minute”, I struggled to find the right words, but they were probably unnecessary anyway. Certainly everyone who had been in the water with the animals that day had experienced many of the same feelings, and I am sure they were writ large on my face (in big black and white spotted letters!). In swimming with this one particular animal, I experienced a profound connection with a truly spectacular natural phenomenon, one that will provide ample motivation to continue the search for a better understanding of the nature of such things, for long into the future.  These are the moments that launch and tie together a career in biology, and that was the best one I have ever had.

Simple questions with complex answers: why is a cooked lobster red?

Some really simple questions have surprisingly complex answers.  “Why is the sky blue?” ends up being all about differential absorbance of varying wavelengths of electromagnetic radiat… see, there, I’ve already wandered off into jargon land.

And so it is with the question “Why is a cooked lobster red, when a live lobster is not?”.  An odd question, but its exactly that kind of “I wonder why…” moment that has led to some of the greatest discoveries.  Anyway, you can argue that it is not a trivial question; indeed, the name of an entire restaurant franchise depends on the correct color change occurring when you drop a Homarus americanus into a pot of boiling Old Bay.  So what’s going on?

Well, its all about the astaxanthin, (lets call it AXT from now on).  AXT is a carotenoid, which means it’s a fat-soluble pigment that – generally speaking - is red or orange in colour.  Carotenoids give tomatoes their red (lycopene), egg yolks their yellow (lutein), carrots their orange (beta carotene), salmon their pink (canthaxanthin) and televangelists their freakish alien fake tans (but they do offset the glowing white dental veneers ever so nicely, don’t they?).  Lobsters don’t make AXT, they get it from eating their veggies like a good little lobster, because ultimately it’s a plant pigment (plants use it as a sunscreen – but that’s another post for another day!).  In its basic form, AXT is really vivid orange, almost vermilion.  But in lobster shells it doesn’t occur in its basic form; instead it’s mostly bound to a protein, called crustacyanin, which we’ll call CR for short.  AXT binds to CR in much the same way as oxygen binds to the haemoglobin in our blood, except for one big difference.  Unlike oxygen, which fits neatly in a haemoglobin molecule, AXT has to bend to fit into the CR molecule, like one of those freakshow contortionists who fold themselves up in a box.  In bending the AXT molecule to make it fit, the natural colour of astaxanthin changes – it shifts – from red to blue or blue-green.  Historically, this shift has been an interesting mystery to chemists and physicists interested in properties of pigments, because its unusual for the same pigment molecule to have both red and blue forms, as most avid flower gardeners can tell you.  On the right is a picture of the rare all-blue form of the American lobster (read more at the University of Maine website)

Enter Michele Cianci and colleagues from the University of Manchester in England.  These clever folks showed in 2002 that the colour change – technically called the bathochromic shift – is a result of the structure of the CR molecule and the way it flexes the AXT molecule like a loaded spring.  This is where the simple question yields the really complex answer.  Get a load of this phrase from their abstract:  “Recently, the innovative use of softer x-rays and xenon derivatization yielded the three dimensional structure of the A1 apoprotein subunit of CR, confirming it as a member of the lipocalin superfamily. That work provided the molecular replacement search model for a crystal form of the beta-CR holo complex, that is an A1 with A3 subunit assembly including two bound AXT molecules. We have thereby determined the structure of the A3 molecule de novo”.  Ex-squeeze me baking powder?

Yes, well, that's all well and good, but it doesn’t answer the simple question of why they go red when you cook them, does it?  Bear with me…  When next you are at the grocery store, take a look in the live lobster tank and you’ll see that they don't look like the handsome all-blue fellow above; they tend to be a mosaic of colours like orange, yellow, cream, green, blue and brown.  This patchwork arises from varying amounts of free and bound AXT in different layers of the shell, and some other factors like how thick the shell is, and whether the AXT is at the surface or in a deeper layer.  If you go ahead and buy one of these lobsters and drop it into a pot of boiling water, little happens to the AXT because it’s heat stable.  But the protein CR, on the other hand, is not.  Like most proteins, it loses its structure when you apply intense heat, unfolding like a jack-in-the-box, and flinging off the AXT in the process.  Liberated from its oppressive bathochromic bonds, the AXT reverts to its normal colour – intense orange-red.  Et puis, vous voila! – blue/green lobsters turn red when you cook them.

Much the same process happens in shrimp and crabs when you cook them too, but it was worked out for lobsters first because they only have one carotenoid – AXT – whereas other crustaceans had other carotenoids that complicated the picture even further.

PS - some genetic rarities give us all sorts of lobster colour patterns like the all-blue one shown above, but my favourite is the half-and-half.  The first time I saw one of these, I thought it was someone having a joke at my expense, but they're the real deal!  How it happens is still a mystery, but there's probably something wrong with the way they express CR on one side of the body.  Picture from National Geographic.

Tip of the Mackintosh hat to @AboutMarineLife on Twitter, for inspiration.

Cianci M, Rizkallah PJ, Olczak A, Raftery J, Chayen NE, Zagalsky PF, &; Helliwell JR (2002). The molecular basis of the coloration mechanism in lobster shell: beta-crustacyanin at 3.2-A resolution. Proceedings of the National Academy of Sciences of the United States of America, 99 (15), 9795-800 PMID: 12119396

The water is ALIVE!

Its easy to get discouraged about the plight of marine ecosystems and the future of all those incredible marine species that we love so much. This is especially so of late, with all the bad news about the oil spill in the northern Gulf of Mexico and the impacts that it may well have on several habitats. Consider this post, then, as your good news story for the week. I am here to tell you that there is still amazing stuff to see in the ocean. Incredible stuff. Stuff that will blow your mind. I can tell you this with supreme confidence, because for the last two days, that’s exactly what I have been seeing. As part of the research program at Georgia Aquarium, I am with colleagues in Quintana Roo, Mexico, studying whale sharks and other species that live in the azure waters of the Yucatan peninsula. Jeff Reid, who is the aquarium’s dive safety officer, is here and our main colleague in Mexico is Rafael de la Parra of Project Domino, who has been working on whale sharks and other marine species in the area for many years. This is a remarkable part of the world, with a lot of great terrestrial activities (can you say Cenotes, anyone? No? How about Mayan ruins?), exceeded only by the marine life, which is truly spectacular.

Yesterday Jeff and Raffa and I spent the day boating around the northeastern tip of the Yucatan along with videographer Jeronimo. Now, when you’re on a boat, you can only see a small strip of ocean either side of the vessel, and yet over the course of the day we saw lots of mobula (devil rays), turtles, flying fish, manta rays, spotted dolphins and whale sharks. We snorkeled alongside some of these animals and, in the case of whale sharks and mantas, took samples of their food for later analysis. They dine on the rich plankton soup of this tropical upwelling area, much of which consisted of fish eggs, which hints at other fish species – yet unseen – taking advantage of the plankton to start their next generation by spawning in the surface waters. Snorkeling next to a whale shark in the natural setting was a special thrill; I’ve been lucky enough to work with the animals in the collection at Georgia Aquarium since 2006, but this was my first encounter with them in the wild. Except for the slightly different “faces” (we do get to know our animals pretty well) and the parasitic copepods visible on the fins of the wild animal, it could have easily been the very same sharks Jeff and I have been working with in Atlanta.

Today, Jeff and Raffa and I joined Lilia (from the Mexican department of protected areas CONANP) and pilot Diego for an aerial survey of the waters around the northeastern tip of the Yucatan. In contrast to the boat, you can’t get in the water from a plane (its not advisable anyway), but you can see a whole lot more at once and cover a much greater area in a relatively shorter time. From the air, lots of sharks, cownosed rays, manta, dolphins, fish schools and whale sharks were all visible, and I am told that flamingos and manatees can be seen at other times too. The manta rays, which numbered in the hundreds, were especially impressive and included at least two species (see my post about taxonomy of mantas). The sheer number of cownosed rays, called chuchas in the local slang, was staggering (muchas chuchas, if you will). They formed huge schools that looked for all the world like the rafts of sargassum weed that accumulate on the wind-lines at the water’s surface offshore. Many of the turtles and mobula seemed to be in the mood for love; most turtles were in pairs (or a pair being followed by other hopeful males), whereas the mobula followed each other in lazy tandems, their wingtips breaking the surface with every stroke. Whale sharks were also there – lots of them – with their attendant flotilla of tourist boats and tiny orange specks of snorkelers in life-vests, doing their best (and largely failing) to keep up with the gentle giants.

When you have experiences such as those I have shared with my colleagues over the last two days, you are reminded why we do this stuff in the first place. Its not just for the papers, or the salary or the glory of new discovery (yeah, right!), its for those moments working with animals when you and a colleague become friends because you shared an experience of the oceans that most folks will never have. We should seek to share and recreate those moments with everyone we can, whether its in an aquarium or on the open ocean. I am pretty sure that if we could all do that, then public empathy for the plight of the oceans would skyrocket, and many of the threats that face them would be addressed quick smart.

No rest for the wicked

Returned from the Eastern Fish Health Workshop in the DC area yesterday, after our flight got canceled on Friday.  It was a fantastic meeting, for all the reasons I cited in my previous post. 

I've got one day at work today and then off to Mexico for field research with Mexican government colleagues this week (more about that later), but not for long, because teaching duties in NY on Friday and Saturday call.  While I am in NY, I'll be giving a public lecture about whale sharks at Stony Brook Southampton on the 4th at 1930hrs.  Its part of the SoMAS Spring lecture series; I'd love to see you there!

Whale sharks start to give up their secrets

Whale sharks are the largest fish in the oceans; they can grow to 20m in length and weigh many tons, although 7-9m is closer to the common average these days.  Despite their tremendous size, scientists don't know that much about them.  We know that they eat plankton and that they live in the tropical oceans throughout the world and there have been quite a few papers reporting their presence in different waters, but these represent only the most basic foray into the biology of a species.  More recently, there's been a few more including one that explores genetics (Castro et al., see below) and some that have started to explore behaviour (see Brunnschweiler et al.).  Up to this point, the focus has all been external; that is, only the biology that can be observed from the outside.  That's no surprise really; its a logical place to start and there are some huge logistic challenges to working with whale sharks, as you can probably imagine.

There are 4 whale sharks in the collection at Georgia Aquarium in Atlanta and I have been lucky enough to work with these amazing animals since 2006.  Part of that work has involved veterinary examinations, which has allowed us, for the first time, to look at aspects of the internal biology of whale sharks. The first part of that work is now in print: a paper I co-authored with the aquarium's principal clinical vet, Dr. Tonya Clauss, and a colleague from National Aquarium in Baltimore, Jill Arnold (Jill is an expert in medical techniques, especially blood work), which is in the latest issue of Aquatic Biology.  Our paper is a discovery-based one (i.e. not testing a specific hypothesis) about the nature of the blood of whale sharks, both the cells and the chemistry of the blood serum.  Its open access, so you can get it at the journal web page here

In it, we show that whale sharks have blood that is fundamentally similar to that of some other sharks, specifically the bottom dwelling ones like nurse sharks and wobbegongs, but pretty different from the toothy predatory sharks like great whites.  They have very large red cells, actually white cells too, but this is something they share with the bottom dwellers, so it appears to be a feature of the group rather than a function of the size of the whale shark as such.  Whale sharks are the only pelagic members of that group, the order Orectolobiformes.  Why such large cells, then?  Our study didn't answer that question, but my best guess is that they have relatively low metabolism compared to the carcharhinids, which may need the high relative surface area of smaller red cells to improve the movement of oxygen in and out of cells.  This is the first of several hypotheses that we can only begin to pose because of these first discovery-based efforts.

I can't tell you how excited I am that we can begin to share what we've been learning at the Aquarium.  The chance to work with whale sharks is a real gift for a fish nerd like me, and the opportunity afforded by having access to them in the more controlled environment of an aquarium makes it possible to do safely and effectively research that has been prohibitively difficult with free-ranging whale sharks up to this point.  Of course, the ultimate goal is to extend that work to compliment the field research, and I look forward to telling you more about that in future posts.

Brunnschweiler, J., Baensch, H., Pierce, S., & Sims, D. (2009). Deep-diving behaviour of a whale shark during long-distance movement in the western Indian Ocean. Journal of Fish Biology, 74 (3), 706-714 DOI: 10.1111/j.1095-8649.2008.02155.x 

Castro, A., et al. (2007). Population genetic structure of Earth's largest fish, the whale shark ( )
Molecular Ecology, 16 (24), 5183-5192 DOI: 10.1111/j.1365-294X.2007.03597.x 

Dove, A., Arnold, J., & Clauss, T. (2010). Blood cells and serum chemistry in the world’s largest fish: the whale shark Rhincodon typus Aquatic Biology, 9 (2), 177-183 DOI: 10.3354/ab00252