Sleeper shark necropsy!

Posted on by aksealife

Above: Secured! On Nov 26th, Richard, Kenny, Markus, Kaili and Nathaniel finally pulled the dead sleeper shark above the high tide line on Afognak beach, and tied it to a tree. We estimated the animal to be about 10 ft long with a mass of around 300 lbs. We returned next day to conduct a necropsy.

{Warning! This post contains photos of a necropsy which are gory}

 

On November 27th, we got to perform a necropsy on the carcass of a Pacific sleeper shark (Somniosus pacificus) that had repeatedly washed up on Afognak beach, near Seward, Alaska, the week before.

Starting around the 20th, we received several calls about a dead shark washed up on a beach near Seward. Over the next few days, we went in search of this shark several times, only to be stymied by a disappearing shark act due to high tide. On the 3rd attempt on the 26th, we finally secured the shark. Many thanks to Seward citizens Karin Hardy, Marc Swanson, Ann Ghicadas and Deb Cline for repeated alerts, and helping us secure this fine specimen, and to Carol Griswold for the photo shown above.

We returned on the 27th to conduct an on-site necropsy after deciding it would be too difficult to transport this large shark back to the ASLC. We measured, collected samples, and brought the gastric tract only back to the center for a closer look. Carrie Goertz, our director of animal health, and laboratory coordinator Natalie Rouse conducted the necropsy with the assistance of other center staff (Richard, Kenny, Kaili, Chloe, Alyssa, Markus). Here are some interesting photos from this necropsy (photos by Chloe Rossman and Markus Horning, radiographs by Natalie Rouse):

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Veterinarian Carrie Goertz is kneeling close to the sharks tail, looking at one of the two very large liver lobes.
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The tan-yellow elongated ‘bag’ is one of the two large liver lobes that extend from just caudal of the skull all the way to the anus. In sleeper sharks that do not have a swim bladder, buoyancy appears regulated via lipid content of the liver, which may account for up to 1/3 of total body mass.
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The shark has almost no discernible fat beneath the skin. Most of a shark’s muscle mass is ‘white’ muscle as seen in this image, that does not require much oxygen and is used for brief bursts of speed. They also have some ‘red’ muscle which needs a more continuous supply of oxygen but has great stamina, and is used for cruising. This animal has thin bands of red muscle just under the skin and above the white muscle. Overall, this animal appeared to have more white than red muscle, except near the tail. The red mass is part of the digestive tract. The tan mass at the bottom is liver.
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Closeup of muscle tissue beneath skin. Red muscle under skin, white muscle beneath red.
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With the liver removed, the digestive tract with stomach (descending), intestine (ascending then descending) and colon become visible. The large spleen is visible as a triangular mass on the caudal end of the stomach. The gall bladder by the esophagus is leaking yellow bile. Overall, the stomach is large and voluminous, but the entire tract is comparably short.
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The intestinal tract at the Alaska SeaLife Center. Esophagus and gall bladder on left, then the large stomach, with the triangular spleen on right (by pincers), followed by ascending and descending arms of intestine, terminating in the colon. The white spot right below the scaling label (insert) is an infection pustule filled with pus, cut open. There are many others that are less visible as they are not cut open. The animal appears to have succumbed to a cascading series of infections, leading to a fatal sepsis.
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A kidney cut open – while all other organs were in good shape despite a week since death, the kidney was seriously necrotic, likely in part due to infection and sepsis.
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An immature ovary in this female shark. Sleeper sharks are thought to be ovoviviparous, and give birth to about 300 little sharks. The shark was 312 cm in total length. If what was recently published about aging and longevity in the closely related Greenland shark (Somniosus microcephalus) translates to Pacific sleepers, then this immature juvenile female could be about 80 years old. That is however entirely speculative at this point.
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The tiny brain, smaller than two walnuts.
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Natalie is cutting open the very thick cartilaginous skull.
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Here is the heart of this female sleeper shark

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Sharks have comparably simple, two-chambered hearts (diagram is from clipart-library.com), with a single atrium leading into a single ventricle. From the ventricle, blood is pumped via the afferent branchial arteries into the gills, where the blood is oxygenated. From there, blood flows through the efferent branchial arteries to organs and tissues, and back to the heart via veins which terminate in the venous sinus. Pumping action also creates suction within the rigid (!) pericardium in support of circulation, an important feature since sharks have very low blood pressure. The heart is typically located near the head.

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The Ampullae of Lorenzini in the head, just under the skin. They are electroreceptors found in elasmobranchs (sharks).
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Shark skin!!! Sharks essentially have teeth on their skin, which in some countries is used as sandpaper.

And now finally – drumroll please – the business end of the shark:

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Sleeper sharks have very curious dentition. Upper jaws (right side in above image) have curved, triangular, hook-shaped teeth. The upper jaw is used to latch onto larger prey items that are not ingested whole – sleeper sharks are very efficient suction feeders.

Lower jaws have completely different teeth (upper left side of image): these teeth are square-ish, and flat, not curved. They are very small but very sharp. They are used for cutting – scoop style – against the upper jaw. This results in a very large ice cream style scoop being removed from the meal. Or cookie-cutter style, if they twist while scooping, which has been reported. For larger sharks, the scoop can be 50cm or even more in diameter. This animal however only had a mouth width of about 37 cm.

And we’ll wrap up this necropsy photo-blog with some very cool x-ray radiographs of this sharks jaw prepared by Natalie Rouse. Note that a section of each jaw in the overview image has been removed.

Above (left and right panels): lower jaw with razor sharp cutting teeth.

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Upper jaw with hook-teeth for grabbing / latching onto meal. In both lower and upper jaws subsequent rows of teeth are visible in the x-ray. In the lower jaw, only the terminal row is fully exposed and does all the cutting, though a second row can be seen behind the exposed row. In the upper jaw multiple rows are typically exposed, as can also be seen in the large visible light image above.
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Full radiograph of upper and lower jaws

Further learning resources:

Here you can find a well prepared shark dissection curriculum by the RJ Dunlap Marine Conservation Program of the University of Miami.

On the Elasmobranch Husbandry pages you can find a ton of very useful and interesting information on sharks, skates and rays. Very cool!

 

Written by: Markus Horning PhD

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Published by aksealife