BREAKING NEWS: Sleeper sharks as predators of giant squid

joel_ang

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I saw a docu on animal planet showing sleeper sharks along with hagfish and others feeding on a sunken grey whale carcass. The fish really looked slow and senile,maybe a few of the sharks ate a giant squid carcass and was caught before all of it was digested?
 

Phil

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Hmm...this may be a stupid question but 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?

If the sleeper sharks are feeding off corpses, I wonder if the scenario is that they are feeding off drifting bodies or scavenging on the sea bed.
 

MuscaDomestica

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

Fujisawas Sake

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Musca,

I don't think that's a rule, rather that some have been found with parasitic infections. Where'd you hear that? I would like to read the report, mostly because I do take an interest in parasites.

John
 

Clem

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Wow, this is all very weird.

I'd like most to know how far along in the digestive process the squids had advanced before the sleepers were captured, and how long (approx) the sharks had been in the nets before being examined. One possibility is that the sharks find themselves in the nets with the squid and consume them before expiring; that's why I'd be keen to know what condition the squid were in.

Though the sleepers appear quite placid, they are very powerful animals, and well equipped with the sensory panoply that makes sharks such effective hunters. And, despite their huge eyes, even Colossals have blind spots.

:goofysca:

Clem
 

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?
 

Fujisawas Sake

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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
 

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