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brugdemaki caroline

Marine biologist Caroline Aas Tranang displays one of the shark slices.

Photo: Vibeke Lund Pettersen / Institute of Marine Research

The world's largest sushi?

No, this basking shark roll is not recommended for your dinner plate. However, for innovative research, it is perfect. 

This basking shark was found stranded in Sørreisa in the fall of 2023. It's a rare incident for shark researcher Claudia Junge.

"It's the first time I've had the opportunity to see a whole basking shark up close like this. It gives us an incredible opportunity to learn more about this mysterious shark" Junge explains.

«Shark busters» on the move

When the news of the basking shark in Sørreisa came in, Junge gathered a team and headed out.

"We measured its length and girth and took samples while it was still on the beach. Since the shark was in good condition, we decided to transport it to Tromsø, where we placed it in the freezer."

With local assistance, the shark was lifted from the shore and loaded into a freezer truck. Basking sharks can reach up to 11 meters in length. This one measured four meters and is a young female.

A milestone in research

Examining a specimen of this plankton-eating shark species is no ordinary day at the office for the researchers. Ph.D. candidate Antonia Klöcker is halfway through her doctorate on sharks in Norway. For her, this is a milestone.

"It's also a milestone in basking shark research. Internationally, we find only two descriptions of basking shark dissections, both from the 50s. Having the chance to see a whole basking shark up close like this is something I will never forget", Klöcker says.

Read more: Basking shark

Caroline står å sager i haien, mens resten av hai-teamet stiller seg opp bak haien. Det er fem personer og en hai på bildet.
Some of the participants to the dissection, from the left: Caroline Aas Tranang, Antonia Klöcker, Ingrid Marie Bruvold, Axel Schlindwein (UiT) and Claudia Junge. Photo: Vibeke Lund Pettersen / IMR

Read more: Shark summer 2023 

Basking shark in slices

Originally, the plan was to dissect the basking shark in the usual way, cutting open the shark's abdomen, extracting the organs, weighing, and measuring them, and taking various samples.

But upon Klöcker’s initiative, the researchers chose a completely different approach. The shark was measured and cut into 17 cm thick slices while frozen.

"We want to investigate whether the basking shark is a regional endothermic shark. In very simple terms, it means it is self-warming. Endothermic species have heat-retaining properties in parts of their body. They adapt to cold by retaining metabolic heat, for example, in internal organs and certain types of musculatures" Klöcker explains.

Antonia Klöcker og Ingrid Bruvold står sammen og ser på et ark. De planlegger for disseksjonen.
Marine biologist Ingrid Marie Bruvold and research fellow Antonia Klöcker is going through the routine they have planned, before the dissection starts. It requires a lot of logistics and planning to carry out this type of "operation." Photo: Vibeke Lund Pettersen / IMR

Most fish in the sea do not have self-warming properties, but it has been documented in a few shark species and other larger fish that swim long distances, such as tuna and swordfish. To determine if the basking shark is indeed regionally endothermic, researchers are looking for specific structures within the shark's musculature.

"That's why we want slices of the shark. We can analyze the musculature at different locations along the shark's body and maybe find evidence that the basking shark has heat-retaining properties. Irish researchers have already made findings suggesting this", Klöcker adds.

Messy and heavy

Cutting up a 4-meter frozen basking shark into 12 equally sized pieces is not a job for the faint-hearted. It had never been done before, so groundbreaking work took place in the sampling room at the Institute of Marine Research in Tromsø.

"It was much harder than expected, and it took a long time. It also got quite messy after a while" says marine biologist Caroline Aas Tranang.

Along with colleague Ingrid Marie Bruvold, she was one of those who used a bread knife, handsaw, muscles, technique, and patience when cutting up the basking shark.

"We spent two full days cutting up the shark. It was very exciting and very different from what we work on at a day-to-day basis. None of us had dissected a basking shark before, so we didn't know what to expect" says Bruvold.

"The first pieces went fairly quickly, but when we eventually hit the liver and stomach, it became quite messy. It became tough to saw and very messy. We don't need to talk about the smell, but let's just say there were some comments when I returned to the office" Aas Tranang continues.

Well documented

While a team took turns on the increasingly tough cutting job, Klöcker took care of the finished basking shark slices.

"We take high-resolution images of the "sushi pieces" to look for structures, a network of blood vessels that act as a heat exchanger for the shark. The tissue condition was good enough that we also took muscle samples, which, after thorough analysis, can contribute to understanding how the shark's heat regulation works", she explains.

After two days of intense work with the frozen shark, all 12 basking shark slices were cut, cleaned, and photographed.

Puzzle time

But the researchers didn't stop there. The even messier part of the work remained, where the internal organs are removed for weighing and sampling.

"It became quite a puzzle. To weigh various organs, such as the stomach, liver, and intestines, we had to cut them out from each slice, sort and collect them in separate containers. Usually, we're used to seeing whole and neat organs inside sharks, but this is a completely different way of working. Now we had to identify which structures we were looking at based on their contents and approximate location. It wasn't always easy, and it's good to have a solid team with diverse expertise in shark anatomy" Bruvold explains.

The shark's head had a different fate. The jaw, skull, fins, and some other samples were collected by researchers from the University of Bergen and will be archived and stored in the collection at the University Museum in Bergen.





Antonia Klöcker

PhD Student/ Research Fellow/ Research Scholar