Shedd Aquarium helping to reintroduce endangered sharks to native habitat
Backlit with the beams from a flashlight, a figure came into view inside the leathery sac. Called a mermaid's purse because of its shape and size, the zebra shark egg's translucence revealed an embryo.
“See it wiggling around in there?” said Anna Byczynski, an aquarist and supervisor of the Shedd Aquarium's tropical marine habitats.
Scientists use this technique, called candling — which historically entailed holding up a burning candle — to assess the contents of shark eggs for health, viability and genetic diversity.
After passing with flying colors, four of them — laid by the Shedd's 30-year-old “super mom” Cleo in the Wild Reef exhibit — embarked on a 9,000-mile journey, tucked in bags of seawater inside Styrofoam coolers, from their first home next to Lake Michigan to the Indonesian archipelago of Raja Ampat.
The collection of more than 1,000 islands forms part of the so-called Coral Triangle, an area in the western Pacific and Indian oceans home to the richest concentration of marine biodiversity on Earth. It is part of the natural range of zebra sharks, named for the black and white stripes on the tails of the species' offspring.
Officially, however, the species is the Indo-Pacific leopard shark — a name better suited for the adults' spots, which the stripes eventually fade into — or Stegostoma tigrinum (not to be confused with the leopard shark of the eastern Pacific, or Triakis semifasciata ).
Since 2004, over 80 zebra shark eggs have hatched at the Shedd, placing baby sharks at more than a dozen zoos and aquariums across the United States.
Now, the eggs are going international as part of the multi-institutional ReShark initiative to reintroduce populations into the wild and its Stegostoma tigrinum Augmentation and Recovery, or StAR, project, which took off in 2020 — the world's first such effort for sharks.
Zebra sharks tend to rest on reef floors, regulating bottom-dwelling prey such as snails, clams, crabs, shrimp and small fish, an important part of maintaining thriving ecosystems.
But the species is considered globally endangered by the International Union for Conservation of Nature, with populations declining and at risk from targeted fishing for the fin trade and from incidental capture, or bycatch, in fisheries.
“They have essentially been fished to functional extinction,” said Steven Kessel, director of marine research at Shedd. “That means they're no longer playing a functional role in the ecosystem; their numbers are so reduced that they're not really having an impact on the food web.”
The species' coastal habitats, such as mangroves and reefs, have also suffered loss and degradation due to urban development and climate change. According to the international union, 44% of mangrove areas across Myanmar, Malaysia and Cambodia were lost between 1970 and 2020. And rising ocean temperatures have caused large-scale coral bleaching and die-offs since 1997.
Thousands of hours of surveys in the last two decades indicated the presence of only three adult zebra sharks in Raja Ampat's protected waters, which span millions of acres, according to ReShark. Scientists estimated fewer than 20 individuals in the archipelago.
Since 2023, however, the project has released 75 zebra sharks into Raja Ampat.
The four eggs from the Shedd are expected to hatch at the Raja Ampat Research and Conservation Centre, on West Papua's island of Kri, where a team fondly known as “shark nannies” will care for the juveniles.
After hatching, the pups will transition to a sea pen to get used to the natural marine environment and develop foraging skills. They will be tagged and released after they reach an appropriate size if they are in good health.
“This is one of the most rewarding parts of my job,” Byczynski said. “Working with these animals day in and day out is very cool — to be able to take care of the adults and then watch them lay the eggs, bring the eggs up, handle them week after week, and then be able to give them back and aid in this new population.”
Thinking about the pups she cared for as eggs being released into the wild and swimming the waters of Raja Ampat gave her chills, Byczynski said. She rubbed her arms as she looked over to Cleo, who was swimming laps in a tub behind the scenes at the aquarium.
Kessel said the project is a proof of concept for yet another tool in shark conservation, especially as there are still skeptics in the field.
“(Reintroduction) is very common and well proven in terrestrial environments,” he said. “And also in freshwater, there's a lot of restocking. Even in the Great Lakes, they do a lot of stocking, et cetera. But it's less common in marine environments. This is the first time it's been done with sharks.”
Being egg layers makes zebra sharks “perfect” for this approach, he said, but expanding similar efforts to shark species that are more critically endangered will present other challenges, since other species give birth to live young.
The success of the project is creating buzz around the region, he said, among other countries keen to participate in zebra shark reintroduction. And conservationists can use the opportunity to persuade governments and fisheries agencies to improve protections for sharks already in the wild — effecting change, he said, “by being a carrot rather than a stick.”
“The fact that this has been a success is really groundbreaking for the field of shark research and conservation,” Kessel said. “We need to look at all different avenues for conservation management because sharks are so imperiled. There's really a crisis, and we need to be doing everything we can.”
adperez@chicagotribune.com