On November 27th, 2017 – 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):
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 that 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.
And now finally – drumroll please – the business end of the shark:
Sleeper sharks have very curious dentition. The upper jaws (right side in the 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 photoblog with some very cool x-ray radiographs of this shark’s 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.
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!