An unprecedented challenge: The world's first skeleton of the fabled Giant Shark is now on display at Kamogawa Sea World

There are more and more books and movies related to sharks, but have you ever heard of the giant shark with an extremely big mouth?

　It is an incredibly rare type of shark called a megamouth, also known as the massive phantom shark. About 100 specimens have been observed or caught since the species was first discovered in 1976. As such it was quite big news when a megamouth, caught in the offshore stationary net in the sea area of Sunosaki, was discovered in May 2017 by an aquarium in Chiba prefecture,.

　This aquarium is Kamogawa Sea World, a core facility of Gran Vista Hotels and Resort. The keeper, Ahihisa Osawa, remembers the exact time he was rushed to the site after first being contacted.

　"I have been working for the aquarium for the past 27 years, and I couldn't believe such a shark would come to the Boso peninsula. This discovery was only the 111th case in the entire world and the 21st case in Japan. The shark probably swam to the area but was already dead when it was discovered by the seashore. It was then decided to bring the animal to Kamogawa Sea World for research purposes," said Mr. Osawa.

The megamouth shark found was a female, measuring in body length at 5.4m and weighing 1.2 tons. What was the best way to present this precious shark to the world? After researching, marine biologists at Kamogawa Sea World concluded that the best method was to make a "skeleton specimen.”

　There were already a few formalin specimens and taxidermic specimens of megamouth sharks, but skeleton specimens were said to be impossible to create because the shark's bones are extremely soft compared to other cartilaginous fishes. In addition, it was considered extremely difficult due to the immense size of the body.

　"But if you really manage to make it, it will become an invaluable resource. The movements of the creature can be understood by analyzing the bones. If you look at a skeleton, you can easily picture the animal's movement. I thought this was worth the challenge," said Mr. Osawa. >

　With this mindset, the unprecedented challenge of creating a skeleton specimen out of cartilage was undertaken in collaboration with a global shark researcher, Dr. Kazuhiro Nakaya.

While the megamouth shark was stored in a freezer at -30℃ (-54°F), it was decided to first create a sample of the specimen using the bones of a goblin shark, which are said to have a similar composition as the megamouth shark's bones.
　The sample completion brought higher results than expected. Encouraged by this first success, the flesh removal process from the megamouth shark body started in February, the year following the capture. It is said that the whole process took three days, from carefully removing the flesh, to getting to the point where only the bones remained.

"It was impossible to predict what could happen inside the shark's body when removing the flesh. Because the bones were so limp, these could be severely damaged by the teeth of the cutter. It was literally a direct touch exploration," said Mr. Osawa.

　In the specific case of megamouth sharks, because of the way they swallow plankton, these animals have complicated gill structures.
　It is said that the shark’s body has countless branches of fine cartilage that can stretch like ribs, and these were found one by one with great care when removing the flesh.

　And then, March came. All the parts were loaded onto a freezer truck and were sent to a sample-making factory in Shiga prefecture where the bones were soaked in a special liquid. Finally, Dr. Nakaya used his own hands to shape and complete the world's first megamouth shark skeleton specimen.

　Through this exacting process, Kamogawa Sea World managed to develop a new technology. This successful undertaking opened the door to recreating skeletons of other rare sharks and deep-sea creatures. The white bone structure of the megamouth is now on display in the Rocky World area of the aquarium. If you look carefully, you can picture the dynamic movement of the bones when the shark inhaled the plankton, opening its large throat in the deep, dark sea.

　"Looking back, we couldn't imagine we would make such a skeleton specimen when the shark was captured. But after it died, we examined it, practiced it, and all the possibilities just expanded. This project taught me that nothing is impossible as long as you don't give up. This shark now became a skeleton, and we are glad the public can be so close to one of the strangest and yet most fascinating creatures swimming in the Boso Sea," said Mr. Osawa.