In deep water: combatting the extinction of sharks

The latest OIST column in the Asahi Shimbun GLOBE+ is out now! This month we wrote about the shark research that is being carried out at OIST and the University of the Ryukyus. The article is in Japanese, but the original English translation is given below.

In deep water: combatting the extinction of sharks

As the world’s oldest predatory fish, sharks have ruled the seas for over 400 million years, from the shallows to the open void of the deep. But in recent decades, their reign has looked increasingly fragile, set to be toppled by human activity.

Despite their fearsome reputation, very few humans are killed by sharks, with an average of 4 fatalities each year. In contrast, it is estimated that globally more than 100 million sharks are killed each year by humans, a staggering 11,416 sharks every hour. These sharks are predominantly killed by the commercial fishing industry, either for shark fin soup – a famous Asian delicacy – or accidentally, as by-catch while targeting other commercially important fish species. Shark populations are also threatened by recreational fishing and culling practices.

“Most species of sharks give birth to only a few live pups each time, and pregnancies can last up to two years, with resting phases in between,” said Dr. Fabienne Ziadi-Künzli, a marine biologist at OIST. “This slow reproduction means that if they are fished extensively, the population can quickly be decimated.”

Coming from Switzerland, one of only 14 landlocked countries in Europe, Fabienne first completed a masters in biology at ETH Zurich, investigating the potential impacts of hydroelectric power production on freshwater fish in rivers.  But she had long been fascinated with the breathtaking array of marine tropical fish and the awe-inspiring majesty of sharks, with her interest ignited by watching ocean documentaries and growing when she encountered and identified tropical fish on diving holidays abroad.  

Ultimately, she was awarded a MEXT scholarship to study a masters in marine science at the University of the Ryukyus in Okinawa – the ideal location for Fabienne. Not only does the island harbor diverse coral reefs, where she snorkels and dives, but it is also the birthplace of modern karate, which Fabienne both learns and teaches, now as a 3rd Dan. After completing her masters, Fabienne stayed at the University of the Ryukyus for her PhD, before joining OIST as a postdoctoral scholar.

“Initially, I only researched coral reef fish, as shark research can be costly and labor intensive, and collecting samples is often logistically difficult,” Fabienne told me. “But while doing my PhD, Momoko Sakurai, an undergraduate student in my lab at the time, started researching the life history of a shark species in Okinawa. But during her research, questions arose as to whether this species was a unique, unidentified species, which was what I aimed to clarify.”

Japan, and particularly Okinawa, is a global hotspot for shark diversity. Out of over 400 modern species of shark, over a third of these species live and breed in the temperate and tropical waters of Japan.

And now, as a result of this ongoing research collaboration between OIST and the University of the Ryukyus, Fabienne and her colleagues have added two new species of shark to the mix.

Unlike their more publicly-known cousins, such as Great White or tiger sharks, these two new, yet to be named species are spurdogs – smaller sharks, typically growing to around one meter in length, that dwell in the ocean at depths of up to 500 meters. One of the newly-identified species was collected from the bay of Tokyo and the other from waters around Iriomote, a remote island in the Okinawa Prefecture.

“These species were initially misclassified, as spurdogs look very similar to each other, with only small differences in head shape, dorsal fin height and caudal fin coloration,” Fabienne explained to me.

It was only by comparing the DNA sequences of two mitochondrial genes that Fabienne and her colleagues were able to conclude that these were indeed two distinct new species of spurdog within Japan.

Fabienne hopes that her discovery will highlight how little we know or understand about shark diversity and populations in Japan. For Fabienne, shark research in Japan is essential to understand how different populations of shark species have been impacted by fishing, with Japan ranking high in the list of shark-catching nations.

“Sharks play a vital role in the ocean’s ecosystem,” said Fabienne. “When apex predators such as sharks are removed, this can result in cascading effects on ocean ecosystems, impacting many marine organisms.”

Without better data on the number of different species, subsequent stock assessment and investigation of their life histories, she added, sustainable management of sharks is not possible.

Fabienne’s former PhD supervisor, Professor Tachihara, who oversaw the collaboration, agrees. “Some deep-sea sharks are of unknown taxonomy, and a taxonomic review is essential to study their life history,” he said. “Life history research of fish is an important research field that provides basic information for various resource states, their conservation and sustainable effective use. Many sharks are especially endangered, and there is an urgent need to formulate future conservation measures.”

“In Japan particularly, we believe there is a high level of endemism, which means that a particular species is only found in a limited area,” added Fabienne. “When these populations are fished unsustainably without catch limits, then this could ultimately lead to extinction.”

Ultimately, Fabienne believes more education is needed to help people understand how essential these creatures are to the ocean. We all need to be more aware, she said, fisherman and consumers, about how we impact the ocean environment.

In the eyes of Fabienne, Japan is an incredible treasure with a rich diversity of sharks – one that must be protected, or else it could potentially be lost for good.