Authors: Ana Velasquez and Kyle Kolda
This past November, a local wildlife tour company alerted the Bishop Lab of a large object floating in Resurrection Bay. After confirming it was an elusive Pacific sleeper shark (Somniosus pacificus), they hauled the 9ft creature back to the Alaska SeaLife Center. Because these animals spend most of their time on the dark and distant seabed, finding these giants (dead or alive) is a rare and exciting opportunity for scientists. The last time something like this occurred in Seward was back in 2017! Which is why the Bishop Lab was so eager to brave the icy roads and drive to Seward the morning after the shark was found.
The 9ft Pacific sleeper shark (Somniosus pacificus) laid out on the floor of necropsy suite at Alaska Marine Life center because it was too large for the traditional table.
Closely related to the Greenland shark (Somniosus microcephalus), the Pacific sleeper shark is thought to live between 250-512 years! This means that present day adults were just wee shark pups milling about the seabed when the Declaration of Independence was signed! As the largest shark known to inhabit Alaskan waters, these animals may play a larger role in our ecosystem than previously thought. Currently, the Bishop Lab and collaborators are investigating their role as ambush predators.
At the SeaLife Center, under the guidance of Dr. Amy Bishop, graduate students performed a necropsy (or dissection) to discover more about the deceased shark and its species. It took a full team to roll the shark on its side, and it was immediately apparent that one scalpel would not be enough. The shark’s rough skin covered in dermal denticles (tough scales) dulled several blades before the body cavity was accessed. And once opened, the liver spilled out. Thankfully, this was expected, sharks do not have a swim bladder, instead they regulate buoyancy with an oily liver which is less dense than water, and this shark's liver was huge - over 60 lbs.
Dr. Amy Bishop and graduate students Kyle Kolda and Lizi Byrd carefully cut through the connective tissue to free the liver while avoiding the gallbladder
Despite being massive, the team determined that this was indeed a healthy weight for the juvenile male sleeper shark. One by one, we carefully removed the other organs from the shark. Samples of the skin, liver, stomach, intestine, and eye were then individually bagged for further analysis back at the lab to learn more about shark health, aging, or diet. All the while, the team of scientists looked for clues as to why the young shark died but alas, nothing stood out as a reason.
Dr. Amy Bishop and graduate student Ana Velasquez removed the sleeper sharks eye in order to age the shark then cut through 4 inches of cartilage to reach the shark's brain.
After two hours of work, the final organ left to sample was the brain. We were wary that any deep cuts would puncture the brain so took the ‘slow and steady’ approach until finally, past 4 inches of cartilage, the brain was revealed. Laughter erupted in the suite. The 300 lb shark had a brain the size of a walnut!
The shark's brain inside the cartilage skull
Perspectives
The opportunity to see the understudied shark and observe its individual organs as a way to better understand the organism as a whole was incredible! Each team member experienced the necropsy with a different perspective ….
ANA: “I came into the necropsy with a strong background in fish biology and dissection skills, however this was definitely the biggest fish I have ever worked on! The most noticeable difference was the fatty liver versus the balloon-like swim bladder common in fishes. I am very appreciative for the opportunity to participate in the necropsy and thankful to the Seward community for their continued support of marine research.”
NATALIE: S"uch a fascinating experience! It is truly rare to be able to learn from these species, especially after they are deceased. I had no idea the brain would be that small given how large they are! While not as noticeable during the necropsy, the smell that clung and lingered after was also surprising discovery…”
KYLE: “This shark smelled very different from the belugas and porpoises that I am used to performing necropsies on. Luckily for me, I left my work clothes in my car overnight and the smell still lingers.”
LIZI: "Coming from a warm coastal town near the Gulf of Mexico, sleeper sharks (and their close relatives the greenland sharks) have always been the most interesting and mysterious of all shark species to me! I was thrilled to participate in this necropsy with the team, so different from the much smaller seabirds I’m used to dissecting, and I think the smell was well worth the experience. Sorry about your trunk though, Kyle.”
DR. BISHOP: “Luckily most of the sharks we work with for our research are alive, but it is always fascinating to see how unique they are on the inside! We definitely appreciate having the opportunity to collect samples that can help fill in the puzzle pieces about these cool animals!”
As a team we look forward to continuing our research on the pacific sleeper shark and their role in the Alaskan marine ecosystem and sharing our findings.
All shark research is conducted under ADFG Permits CF-21-070, -22-069, -23-005