A shark once pushed to the edge in Indonesian waters is now swimming free again, thanks to a captive breeding program that has released what organizers say are the first rewilded sharks in the world.
ReShark, an international consortium of 60 aquariums in 15 countries, spent three years building the program for zebra sharks, also known as Indo-Pacific leopard sharks. The species had become extremely rare in the wild after being overhunted.
Since ReShark’s work began on the Indonesian island of Raja Ampat, 82 captive-reared shark pups have been transported to the island and released into a 46,000 square-kilometre shark and manta ray sanctuary.
The sharks have been fitted with satellite tags, allowing ReShark to track how captive-bred animals behave after release. The group says the sharks are foraging well and staying within the sanctuary’s boundaries.
“Back in 2019, in Raja Ampat, we estimated that there were about 20 individual adult sharks remaining,” Mark Erdmann, executive director of ReShark, told CNN in an interview.
“Most conservation activities for sharks usually revolve around either setting up marine protected areas or doing fisheries management. In our case, our niche is we’re doing active recovery.”
The zebra shark was suited to the program because it lays eggs, a trait shared by 43 percent of sharks. Rewilding programs are usually used for mammals and other terrestrial species, but ReShark says this is the first time the method has been used for sharks.
The project began after Erdmann visited the SEA Aquarium in Singapore and staff told him their zebra sharks were producing large numbers of viable eggs. Pups were hatching faster than the aquarium could manage.
Now aquariums involved in the program send viable eggs in special containers to ReShark nurseries in Raja Ampat and Phuket, Thailand. The eggs hatch there, and the young sharks are raised in protected nurseries by trained aquatic animal husbandry specialists known as “shark nannies”.
When the sharks reach 1 metre in length, they are released into the sanctuary. They are expected to take between five and 12 years to reach sexual maturity.
That means the central test for the program is still ahead, whether the released sharks will reproduce in the wild. ReShark expects the earliest results in 2028.
Overharvesting by Thai and Indonesian locals for shark fins was one of the main drivers of the zebra shark’s decline. ReShark is also working to involve islanders and fishers in the project so they understand the shark’s vulnerability and its role in the ecosystem.
If the effort succeeds, it could provide a model for other egg-laying shark species. ReShark expects the earliest results in 2028.
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