BREAKING NEWS: Sleeper sharks as predators of giant squid

mikeconstable

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Eye parasites

Have read that many Greenland shark (Somniosus microcephalus) have a crustacean parasite living on the eye which must render the fish virtually blind. The thought has been raised that they may attract fish by emitting light?
Mentioned in "Sharks of the World" by Rodney Steel, but remember reading more than I can find in that book.
 

Clem

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First, big thanks to um.... for supplying Cherel & Duhamel’s paper. VERY interesting stuff.

Although the sleeper shark may be the most spectacular individual shark surveyed, I gotta say, the lantern shark is just as interesting. The ventral surface of this small shark is luminescent, which has led some to speculate that this schooling animal uses light to maintain cohesive formations in the lightless, benthic realm. These schools should also be capable of killing prey items much larger then the individual sharks (which average less than 18 inches in length). (I think schooling attacks on Mesonychoteuthis may have been proposed by some smart person over in the “Colossal Squid Necroscopy” thread.)

Somniosus, the sleeper, is described by Cherel & Duhamel as an almost exclusively benthic predator and scavenger, but in other parts of the world the local sleeper variants are known to feed at the surface, especially where carrion and offal are ejected by fisheries. In that scenario, they would likely follow the trail of descending bits up from the deep to the source. For the most part, however, sleepers stick to the mud. What sticks out from Cherel & Duhamel’s benthic model for Somniosus is the presence of big Architeuthis, up to 220cm mantle length as indicated by recovered beaks. If Archis become more ammoniacal as they mature, and “sink up” when they die, then it seems unlikely that these very large specimens found in Somniosus were scavenged off the sea-floor. Does Archi spend time in the mud, then, or is something else happening?

As for the lack of the vicious scarring about the head associated with Mesonychoteuthis in their death throes, perhaps Somniosus has a particularly thick skin? One very interesting thing about the sleeper is the fact that fish found in its stomach often lack tails. If the shark does in fact use luminescence about its eyes to attract prey, then the tail-less condition of the fish can be explained by the head-first attitude of the attracted prey; they swim in for a look, and the shark snaps them up, severing the caudals. Likewise, if Somniosus of the Antartctic is using glowing peepers to reel in big squid, it can dispatch its prey quickly enough to avoid being injured by arm-hooks.

The bottom of the Southern Ocean must be a scary place.



:archi: :goofysca: :mesonych:

Clem
 

Steve O'Shea

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Clem said:
What sticks out from Cherel & Duhamel’s benthic model for Somniosus is the presence of big Architeuthis, up to 220cm mantle length as indicated by recovered beaks. If Archis become more ammoniacal as they mature, and “sink up” when they die, then it seems unlikely that these very large specimens found in Somniosus were scavenged off the sea-floor. Does Archi spend time in the mud, then, or is something else happening?

Archi's of 220cm ML are female and fully mature/spent. I'll bet a dollar that these animals were not taken in Antarctic waters (about as sure as I am about anything anymore), but were recovered from sharks in subantarctic waters, or sharks that have undertaken some migration from subantarctic waters, or were taken next to some Antarctic/subantarctic water mass convergence. I've yet to read the paper ... tiz sitting in my briefcase right now ...

IF Archi truly is found in the Antarctic then it will open up a can of worms ..... Maybe there's another large-bodied squid down there with Architeuthis-type beaks (this cannot be discounted if the beaks are truly Antarctic in origin). My office is full of worms ... nothing surprises me anymore ... deja vu.

I don't know what effect temperature would have on buoyancy; anyone want to comment?
 
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Wait, Steve... Didn't you and Kat hint that there were possibly more than two species of "Giant" squid?

Hell, the Japanese recently discovered a new species of rorqual, Balaenoptera omurai, so stranger things have happened... Of course, they did KILL IT, but it was a discovery, nontheless.

Sushi and Sake (Hold the Whale Meat, please...)

John
 

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Steve O'Shea said:
I don't know what effect temperature would have on buoyancy; anyone want to comment?

Unless there is something funny with ammonia (I've worked with gallons of the stuff but only at room temperature) then cooler water is denser and so has a greater bouyancy but if it cools the squid then the squid will also be less bouyant. However, a dead squid would tend to cool and so become less bouyant and, atlhough you'd pos. have to do some sums, a dead squid would be more likely to sink in colder water than warmer water. You could imagine a current carrying dead squid carcasses into colder waters where the squid might sink to the bottom.

For a simple explanation see:

http://gpc.edu/~pgore/Earth&Space/buoyancy.html

[edit: It would be easy enough to do a quick experiment - get a balloon and fiddle with adding air and a bit of water until it has bouyancy and then warm the water]

Emps
 

Steve O'Shea

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Emperor said:
You could imagine a current carrying dead squid carcasses into colder waters where the squid might sink to the bottom.

Ja.... magnificent! I can imagine this - a colossal graveyard, where all of the spent, ill and dead individuals gather and get picked off/eaten by the seadog scavenging whales and shark.

Even a sperm whale with grossly deformed/damaged jaw lives, eats and survives .... so maybe this big brute bull whale is doing no more than scavenging on the seafloor in this Colossal Graveyard. The scars on the hides of the whales could then become scars caused by live Colossal Squid attacking the whale (and the whale was lucky to survive!!!).

Ja ... it all makes sense now :biggrin2:

:heee:
 

jmccor

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MuscaDomestica said:
Don't the sleeper sharks also have a copepod that lives in one of their eyes, effectively making them blind?

Greenland shark (Somniosus microcephalus) has been posited as the predator off Sable Island (off Nova Scotia) that has been leaving a modest carpet of dead harp/grey seals on the beaches ... with eerie spiral strips of flesh torn off their bodies. A documentary on Cdn TV showed the seals swimming around the sharks (major parasites tangling off both shark eyes) and, again, it's hypothesized that the parasites act like a lure ... the seal investigates ... BAD idea ... the shark grabs a flipper ... voila. Spiral skin tear avec blubber.

Picture of wound 2/3 down on this page:
http://www.conservationinstitute.org/sharkattacks.htm

Major researcher involved is Zoe Lucas.

James McC.
 

um...

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Phil said:
...if Architeuthis body tissues are saturated with ammonia keeping the animal buoyant, following death would one expect the carcass to rise to the surface, remain floating at depth with a neutral buoyancy before breaking up, or sink to the bottom? Without propulsive power from the fins would the dead animal rise like a cork in a bottle or do the ammonia ions keep it perfectly in balance, as I suspect?

Now there's a topic that could use its own thread in the Physiology and Biology forum.

My (probably weak) assumption would be that the squid would 'prefer' to maintain slight negative buoyancy, or at least to err on the side of negative buoyancy. If this information is correct, and I see no reason to doubt that it is, then Architeuthis spends a lot of its time with its funnel pointing downwards. Since the beast has to breathe, I figure that it would make sense to at least have the option of utilizing the exhalation current to offset any sinking which might occur. Or, stated a bit differently, it might make sense to have negative buoyancy to offset any upward momentum caused by exhalation. (Unless the squid sits 'upside-down' in the water and bends the funnel upwards...) I wonder: How 'softly' can the squid breathe, and how much commotion would arise from relying primarily on the fins to maintain depth? Being positively buoyant seems a bit detrimental in terms of stealth and energy efficiency. Also, I'd expect that 'down' is probably a safer direction to go than 'up' into brighter, warmer water. It seems that it would be harder to breathe, harder to hunt, and easier to get eaten up there.

However, at least some dead Architeuthis do float to the surface. This leads me to think that I might be speaking out of the wrong end of my digestive tract again.

Here's a few other questions that have just popped into my head:

Would there be much of a change in buoyancy after an egg mass is released? Without really thinking about it, I would presume that such an event would slightly increase the density of the squid.

Does the ammonium chloride solution in an Archi's tissues have a different coefficient of thermal expansion than seawater?

Do we have any idea at all what mechanism might be involved in regulating the concentration of ammonium chloride in the squid's tissues? How finely and rapidly can the concentration be tuned (assuming that it even can be)?

:sleeping:

:archi: :confused:
 

Phil

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Great post um..., I see where you are coming from. Here's another question to add to your list...

Does the salinity of the seawater affect the bouyancy of squid? I wonder if the latitude and the relative salinity of the seawater has any effect on whether an Archi floats or sinks? Are comparative levels of salt content of seawater a common factor with Archi strandings?
 

um...

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I'm almost positive that it does/is. That's what got me thinking about how well the squid might be able to adjust the concentration of ammonium chloride to account for the changes in ambient density that it will invariably encounter. Now, I would assume that an Archi who's pushing up the plankton (:notworth:) is no longer capable of adjusting its buoyancy very quickly at all and, upon drifting into denser water (if it even gets the chance), will float up to the surface.

Another thought: Since the arms and tentacles are probably more tasty and easier to eat than the rest of the carcass, I would expect them to be nipped off more quickly by scavengers. Since they're also less buoyant than the rest of the body (on average), it would follow that their removal would cause the remainder of the squid to rise to the surface (if it was near enough to neutral buoyancy to begin with).


What effect does decay have on buoyancy?

Is upwelling any sort of a factor here?
 

mikeconstable

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Thoughts?

When ammoniacal squid die, the ion channels that maintain the inbalance of internal/external ions would stop working (but not necessarily quickly?)
So ammonia would diffuse out, and sodium in, making the carcase increase in density.
Steve O'Shea says these creatures make everything stink - do they also have high concentrations of organic amines (which are also likely to be water-soluble, and degrade to ammonim salts)?
 

um...

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um... said:
...how much commotion would arise from relying primarily on the fins to maintain depth?

Probably not much. We're talking about a buoyant force of just a few pounds (sorry, a couple dozen Newtons) here, right?

Also, density changes in seawater are generally just a few parts per thousand, aren't they?
 

ika-san

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On the question of a lack of skin markings on the sleeper sharks raised earlier in the thread...

Assuming, as we are, that struggle marks seen on whales are scar tissue from squid attacks, when the squid tentacles and/or arms get a good purchase on the skin. Whale skin is relatively smooth and flat and, I would think, does not resist the toothy edges of squid suckers.

Having felt skin samples from some shark species, I recall it being somewhat rough to the touch, almost like a cat's tongue. I think the squid tentacle and arm "teeth" may have some difficulty getting any sort of hold on a shark. No hold, no mark and no scar. Sound plausible?

Does anyone know if the sleeper shark's skin has a similar texture to that of other sharks?

- Ika-san

PS Perhaps I hould consult "TSDNMO" - The Shark Dermatologist's News Magazine Online... :jester:
 

Clem

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ika-san said:
I think the squid tentacle and arm "teeth" may have some difficulty getting any sort of hold on a shark. No hold, no mark and no scar. Sound plausible?
ika-san,

Check out the photos below of a Greenland shark, Somniosus microcephalus. This sleeper's battered skin actually looks a lot like a sperm whale's, with an especially big transverse scar atop its head. (You can also see a copepod fastened to the shark's cloudy left eye.)

download.php


What really caught my eye was the circular scar visible on the shark's flank, below the first dorsal fin. My first thought was that it might be the mark of some parasitic fish which rasped or bit out a plug of flesh, but then the scar ought to be a solid, light colored infill of new tissue; this mark is a circular line. It does look a lot like the marks left by giant squid on Physeter. Maybe they ain't so tough?

Somniosus microcephalus has been documented in one of Architeuthis's known haunts, Trondheimsfjord, Norway. Click here to see a local example.

:?:

Clem
 

aron hills

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This topic has even made it into the latest edition of 'New Scientist' (No 2434 - 14th Feb 2004). It really does just repeat what we already know, but at least it is raising the topic with the wider scientific community.

FACINATING STUFF.

:whalevsa:
 
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