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Entries in sharks (10)

Thursday
Mar242011

Why's it always gotta be about poo?

After the outrageous popularity of a previous post here about a whale shark dookie so big you could see it from an aeroplane, now this YouTube video of a white shark telling some cage divers exactly what he thinks of their taste in SCUBA fashions:

At the risk of being labeled “Dr Shark Poo”,  I have a few quotes in this article discussing exactly what’s going on here.  In short, why is the poop yellow? (digestive and blood pigments) why are the fish eating it? (nom nom nom) and why study shark poo anyway? (a figurative treasure trove of physiological data). Roll over there and check out the rest of the article.

Tuesday
Dec212010

Chalk up a win for shark conservation

Yesterday the US senate finally passed the Shark Conservation Act that had passed the House of Representatives back in March 2009.  After an approval vote in the House, it can be signed into law, probably during this session.  David at Southern Fried Science has an interesting post about whether this is *entirely* a win for sharks, since it still contains language that would allow limited finning of smooth dogfish (but see my comment on his thread).  On balance, though, any legislation that brings wider attention and some better legislative regulation to shark fisheries is a move in the right direction.  Perhaps one day we’ll see a blanket ban on finning, but in the meantime I’m happy to call this one a pretty big win.

Tuesday
Dec212010

Sharky Christmas swag

David Shiffman at Southern Fried Science passed along this opportunity to get some sharky swag for your loved ones and help the American Elasmobranch Society student arm as well.  SO, go get some, and feel good that your purchase is helping students of shark science!

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Are you looking for a great source of shark-themed gifts for yourself or the shark nut or SCUBA Diver in your life? Are you looking for an easy way to help sharks and support science? Check out the American Elasmobranch Society’s Student Store!

The American Elasmobranch Society (www.elasmo.org) is the primary scientific society of shark researchers, and they take pride in making sure that deserving student shark researchers can afford to travel to the AES Conference each year. Though they budget funds towards this, students like to do our best to help by running the AES Student Store.

You can find all sorts of good stuff, from shark shaped bottle openers to shark-covered Hawaiian shirts and everything in between. New items this year include shark fin shaped ice cube trays, cookie cutters, aluminum water bottles, and blown glass Christmas Tree Ornaments. Check it out, and know that you are helping a good cause as your shop!

If you order by Tuesday morning, items should arrive in time for Christmas.

Older items can be found here:
http://www.elasmo.org/market.php

And here:
http://www.cafepress.com/elasmobranch

The new items can be found here:
https://sites.google.com/site/aesnewproducts/

Friday
Aug062010

More on sharky parasites

I have a guest post over at the aforementioned Parasite-a-Day blog today. 

Wednesday
Aug042010

Why should sharks get all the glory? - its shark *PARASITE* week too

 Everytime you sit down to watch a premiere in this weeks Discovery Channel shark week, I want you to imagine something: every single shark you see is loaded with parasites.  All of them.  On the gills, sometimes on the skin, and especially in their unique spiral valve intestine, live a myriad critters that make their living off the top predators in the ocean.  Which makes you wonder, are they really the top?  Hmmmm….

In celebration of this carnival of diversity that exploits our toothy friends, AMNH curator/blogger Susan Perkins (ably supported by a veritable Who’s Who of fish parasitologists from around the world) is hosting a parade of bugs for shark week on her blog Parasite-a-Day. Here’s what she’s had so far:

August1. Anthobothrium, an elegant tapeworm.  Yes, I said elegant.  You got a problem with that?

August 2. Gnathiid isopods.  The ticks of the marine realm, blood meal anyone?

August 3. Branchotenthes robinoverstreeti.  A six-suckered monogenean from the guitarfish

August 4. Pandarus rhincodonicus.  A parasitic copepod that likes to hitch a ride on the lips oif whale sharks.

Keep an eye on the blog for the rest of the week and beyond.  Its a fantastic showcase of parasite diversity

 

Tuesday
Aug032010

Shark Week is here

In the past I've had mixed feelings about Discovery Channel's "shark week".  Its great for raising the   profile of our toothy friends, but it has tended to dwell on the gory or sensationalist stuff in the past.  This year, though, they seem to be pushing the conservation and science end of things a bit more, which of course makes me happy.  Georgia Aquarium (my employer) is their partner this year on the website, and they are featuring the web cam from our Ocean Voyager exhibit, which houses manta rays, whale sharks, lots of other sharks and a great teleost (finfish) collection too.  They're also hosting website Q&A with aquarium shark experts (tonights is at 10PM) after each premier on the TV channel, and vignettes from life working with sharks at the aquarium, including a couple of my lab-coated self.

So if you're into sharks, check it out.  And if you don't totally dig sharks - well, what's wrong with ya? 

Thursday
Jul292010

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...

Monday
Jul122010

Whats in a name? Origins of the word "shark"

To a recent roundup of whale shark news, I appended a sort of human interest one-liner about how “shark” is the only word in the English language that derives from a Yucatec (Mayan) Indian word – “Xoc” (pronounced like “shock”). It was just one of those factoid tidbits picked up somewhere along the line of life, maybe while working in Mexico, I don’t remember. It tickled some interest from blogger @hectocotyli on Twitter, who posted a follow-up tweet questioning whether this was actually true, and citing a paper by Tom Jones, from the 5th Palenque Roundtable in 1983. That paper is entirely devoted to the question of the origins of the word shark. I read it and was transported, what a great story! So here it is then, a deeper look at the origins of this word "shark", with thanks to @hectocotlyi for having an inquiring mind and for finding the paper.

According to Jones, the very first mention of the word shark in association with the animal for which we use the name today was in a 1668 work by John Wilkes. One of the first mentions of the word in a diuctionary, however,  is in an anonymous work from 1689, which defines a shark as a “shifting knave”. In other words, a crook, dodgy sort or general baddie. That was surprising to me, because I had just assumed that the use of shark for a shifty character was a much more modern one derived from the noun referring to the animal wif de big nasty teef. Bailey’s Dictionary in 1724 used “scearan” as the likely origin for the word: a saxon term meaning “cut to pieces”. Webster took a different tack in his 1828 dictionary, accepting a theory that it comes from the greek word “carcharias” (sharp tooth), even though that word clearly has a typical Greek hard c sound, not the soft start of shark. These days, Oxford English Dictionary just says “of obscure origin” and to me that might be the best answer, if you insist on a European etymology.

The major alternative explanation is that the word comes from the Yucatec Indian word “xoc”. Now, explaining what the word xoc means in Mayan is not as simple as it would be for European languages; Mayan language groups are apparently among the most arcane and problematic for linguists to study, especially for the bizarre glyphic written forms. Jones goes into the issues in great detail, and its a fascinating read, but I could summarise by saying that at best the word refers specifically to sharks as we know them, and at worst to an ill-defined group of toothy aquatic animals that might also include large fish, crocodiles and toothed whales, in both fresh and salt water. There’s lots of usage examples to support the idea that it means sharks, though, including “xoc yee halal” which are arrows with sharks teeth for points, and “uayab xoc” which is a sort of demon or were-shark, part man and part shark. Its not that simple though, because xoc can also mean “to count to” or to refer to dates ahead or behind. In Mayan glyphic writing, glyphs are apparently freely substituted for other words or parts of words that are pronounced in similar fashion, even though the agreed meaning of the glyphs (or bits of ther glyph, sort of like syllables) may be radically different, which really confuses the issue and is a big part of the reason why written Mayan took so long to decode. In the glyphs from the Jones paper shown below, for example, the middle glyph is a counting glyph with the same meaning as the one on the right, but incorporates the glyph for xoc, of which the stand alone version is shown on the left. To me another obvious clue here is that the glyph for xoc is the head and mouth of a beast, even when used to mean "to count",  which seems to fit well the definition in the broad sense. The beast even has a rostrum of sorts, and triangular teeth.

If the usage roughly matches, then, how would a Mayan word make it to English?  Given that the Spanish and Portuguese were in closer contact with the New World earlier than the English, why would English not pick up the Spanish “tiburón”.  Put another way, why does the Iberian word not also resemble “xoc”? If it’s true that shark is of Mayan origin, then it must be a standalone jump – somehow going from Yucatec to English, skipping Spanish and Portuguese.  For the etymologists, it seems that this lack of intermediate steps or of words that share the same origin, which they call “cognates”, is a real problem for accepting the Yucatec origin of “xoc”.

Jones proposes a way that this could have happened, on the expeditions of John Hawkins from England to the Caribbean in the late 1560’s (incidentally, Hawkins was a pioneer of the English slave trade). Further, Jones proposes that the critical moment may have been an unanticipated battle between Hawkins and some Spanish ships forced to share moorings near Campeche in 1569.  The fight resulted in the destruction of several vessels from both sides and some pretty heavy losses, with over 200 of the English eventually consolidating onto a single ship called the Judith and heading for home.  Jones suggests that a shark frenzy feeding on the unfortunate victims of the battle – and on those who died of hunger and disease on the crowded Judith over subsequent days - might have created an indelible impression on the English (only 15 of whom made it back to Cornwall), enough to cement in their lexicon the local name for these demons of the sea.

As a complete linguistic noob, I find the proposed Mayan origins of shark to be more plausible than the Greek or Saxon suggestions. More importantly, though, it’s a way better story, and when there’s that much uncertainty, I’ll always choose the explanation that involves the greater ration of mysterious glyphic languages and dramatic ship battles on the high seas, wouldn’t you?

Friday
Jul022010

Implications of the first sighting of whale sharks in the gulf oil slick

I recently experienced a moment of genuine dread regarding the oil spill in the Gulf of Mexico, and it was neither a familiar nor comfortable feeling. What is it that invoked such a powerful feeling after a disaster that has been underway for the last 80-odd days, now? Something that struck a little close to home, of course: the first direct impact to whale sharks. You may have seen this story coming across the wires over the past two days about NOAA scientists who, while on an aerial survey of the impacted area, observed 3 whale sharks swimming among ribbons of surface oil, not 4 miles from the epicenter of the Deepwater Horizon spill. This observation has serious implications; let me explain.

Whale sharks are widely-ranging tropical migratory sharks that are unusual among their more toothy relatives in that they eat plankton. Two of the adaptations they use to pursue this lifestyle – surface filter feeding and an exquisite sense of smell – make them especially susceptible to the impacts of the oil spill. I had all but convinced myself (perhaps wishfully thinking) that whale sharks would be able to sense the altered chemistry of the affected water bodies and avoid the area. It now seems that this is not the case; the observation by the NOAA scientists suggest that either whale sharks cannot tell the difference between polluted and unpolluted water, or they can tell the difference but do not alter their behaviour in such a way as to avoid the ribbons and plumes. As USM researcher Eric Hoffmayer states in the article, this is the realization of the worst fears of whale shark scientists, and I count myself among those.

How can it be that whale sharks are unable to tell the difference if their sense of smell is so good? One simple explanation is that the olfactory abilities may be extremely selective. Scientists don’t know exactly what sort of chemicals whale sharks are homing in on when they seek out patches of food in the ocean – indeed, addressing this question is one of the goals of this year’s whale shark research program at Georgia Aquarium – but we have some good candidate molecules. If the whale shark sense of smell is highly tuned to these compounds and relatively insensitive to other families of chemicals, like hydrocarbons (oil and gas), then it’s certainly possible that whale sharks simply cannot detect the problem.

That’s when the second adaptation, surface filter feeding, becomes a liability for whale sharks trying to negotiate the deadly emulsions and surface slicks in the Gulf. To fully appreciate why this is such a problem, we need to look a little more closely at the filtration apparatus whale sharks use to feed.

Like most plankton-feeding fishes, whale sharks use filters in the mouth/gill cavity to sift food particles from the water (see the exellent illustration by Emily Damstra at right). And like most plankton-feeding fishes, these filters develop from structures associated with the gills and gill rakers (cartilaginous rods that come off the leading edge of the gills and protect the gills from fouling and shape the current of water across the breathing surface). Where whale sharks differ radically from other planktivores like, say, anchovies, is that they do not have feathery interlocking gill rakers that serve to filter the plankton but can be disengaged from each other to allow bulk water flow out through the gill opening. Rather, their filters are so derived and so heavily branched that they form a single continuous pad that occupies the space between gill arches; it looks a lot like a black scouring pad. The gill arches cannot be disengaged from each other; thus, anything that goes in the mouth must be small enough to pass through the filters (less than 2mm, or about 1/12th of an inch), or it must be swallowed, or be spat back out through the mouth (something they are surprisingly good at!). In a paper currently in the review process, comparative anatomist Phil Motta from USF is describing the full functional anatomy of these structures; he took the photo of the filter pad surface shown hereabouts based on material samples from Georgia Aquarium.

The implication here is that oil that finds its way into the mouth, if it is not to be swallowed or to foul the filters, must be continually spat back. OK, I hear you say, perhaps if the whale sharks avoid feeding, there won’t be a problem. If only it were that easy. Whale sharks do not only use their mouths for feeding, they use them for breathing. They need to be passing water continually across the filters and thence across the gills, in order to keep the body supplied with oxygen. For the whale shark swimming in oil-affected waters, therefore, the animal’s breathing needs and the susceptibility of their feeding filters to fouling are in complete opposition.

If whale sharks are swimming into oil-polluted waters and fouling their filters with oil, what does that mean? In my best estimation, it means that the oil spill represents an extremely serious threat to whale shark health. I am by no means the first person to suggest this. Nature identified whale sharks as one of the 5 species most likely to be affected by the oil spill, and other scientists like Bob Hueter from Mote Marine Laboratory have also highlighted the risks. The true toll that the spill exacts on the Gulf of Mexico whale shark population will not be known for some time, but the thought of dead or dying whale sharks sinking silently into the depths (dead sharks generally sink, not float) is yet more motivation to put an end to the spill and to undertake immediate and extensive research and conservation programs to assess the damage and plan a road to recovery for the whale sharks – and all the other affected wildlife – in the Gulf of Mexico.

Monday
Jun212010

One of the bizarrest parasitic relationships you will ever see

This post was chosen as an Editor's Selection for ResearchBlogging.orgResearchBlogging.orgMy good colleague Janine Caira wrote a paper way back in 1997 about one of the strangest parasites ever recorded in an animal.  This paper has stuck with me ever since, I think because I saw the original photos when I visited the lab of one of the other co-authors George Benz, when he was with Tennessee Aquarium (he's now at Middle Tennessee State U.).  So, I thought I'd revive it for you guys; the story goes like this:

Janine and her co-author Nancy Kohler had received a report from a longliner of a really big foul-hooked shortfin mako caught near Montauk, NY.  (a shortfin is shown at right, from discovery.com, this one with plenty of parasitic copepods on the dorsal fin - it sucks to be a shark sometimes).  Now, Janine is the queen of tapeworm taxonomy in sharks and rays - believe it or not, there's lots of them - and had visited Montauk before to collect parasites during catch-and-kill shark tournaments held there.  To make the most of the unfortunate death of this mako, they raced across the sound from Connecticut to collect parasites from the beast.  It was a huge animal, nearly 900lbs, and during necropsy, as they say in the paper, they "were astonished to find two anguilliform fish in the lumen of the heart".  Thats right, eels; this shark had two eels living in the chambers of the heart!  These particular eels, called pugnose eels or Simonchelys parasitica, have been recorded before burrowing into the flesh of halibut and other large North Atlantic fishes (hence their species name), but never completely internal and certainly not in the lumen of the heart, so this was a truly remarkable find. 

Janine and her colleagues were unable to determine the path of entry, but they showed good evidence that the eels were alive in the heart prior to the shark being killed and put in the fridge, because their guts were full of blood and there were pathologic changes to the heart.  Their conclusion?  That this was a facultatively parasitic relationship.  In other words, the eels didn't need to be living in the sharks heart (that would be obligate parasitism), rather they took advantage of an opportunity to get a meal.  They proposed that the eels probably attacked the shark after it had been hooked and was dangling, distressed, from the longline.  They had some evidence that the shark was probably resting on the bottom, which may have made it easier for the eels to find.  The pugnoses somehow gained entry (hypothesised to be through the gills) and made their way to the heart, where they dined on the beasts blood up until it died.  Maybe they would have burrowed out again after the animal expired, maybe they would have suffocated (remember - the eels had be swimming in and breathing the sharks blood once they were inside, how bizarre is that?).  We'll never know because the carcass went in the fridge, which ended things for the eels, but also led to this amazing discovery.

The horrifying part is that the shark was almost certainly alive as the eels made their way into its flesh and began to consume its life blood from the inside.  It would have been a long, slow and nasty way to go out.  It just goes to show that even when you are at the top of the food chain, you're never really at the top of the food chain...


Caira, J., Benz, G., Borucinska, J., & Kohler, N. (1997). Pugnose eels, Simenchelys parasiticus (Synaphobranchidae) from the heart of a shortfin mako, Isurus oxyrinchus (Lamnidae) Environmental Biology of Fishes, 49 (1), 139-144 DOI: 10.1023/A:1007398609346