Scientists Release Record-Breaking Number of Baby Seahorses Into Sydney Harbor

After months of painstakingly rearing hundreds of baby seahorses, Australian marine scientists released the tiny animals into Sydney Harbor last week in a major victory for conservation efforts to boost the endangered sea creature’s population.

It was a record-breaking achievement—with roughly 380 baby White’s seahorses introduced into the wild waters of Chowder Bay, the effort marks the largest such release in the world, as David Harasti, a senior research scientist at the Port Stephens Fisheries Institute in New South Wales, tells the Australian Broadcasting Corporation’s Declan Bowring.

The animals’ destination? Eight custom-built “seahorse hotels” made from biodegradable metal. Researchers have been using these cage-like structures for several years to provide a safe place for the teacup-sized fish to eat, live and hide from predators.

Meanwhile in Australia:

Scientists are creating "underwater hotels" to provide a safe haven for endangered seahorses.

The hotels, made of biodegradable metal and covered with algae and coral, act as a natural reef and aim to restore their population.pic.twitter.com/jkqkN6jw6a

— Goodable (@Goodable) July 21, 2023

The White’s seahorse was classified as an endangered species by the International Union for Conservation of Nature in 2017 due to habitat loss, floods and pollution. In some areas of the bay, more than 95 percent of the seahorse’s population has died out over the last decade. Since then, scientists have been researching ways to boost their numbers.

“Seahorses are often considered a flagship species for conservation,” marine biologist Mitchell Brennan, the project manager, tells Reuters’ Cordelia Hsu. “We’ve seen dramatic population losses, which means that we need to act now in order to help these guys persist into the future.”

In 2018, Harasti created the first “seahorse hotel” prototype after noticing while scuba diving that the animals tended to group around old crab traps and anti-shark netting. Scientists have since built more of the structures, which they installed in the habitat about a month before the release. This extra time in the water allowed for algae, corals and sea sponges to cover the hotels, attracting tiny marine creatures that seahorses eat.

The babies released last week were born from three pregnant male seahorses collected from the wild in January. Each of the males can give birth to more than 100 babies, measuring less than one centimeter in length (roughly the size of a grain of rice). They lived at the Sydney Institute of Marine Science aquarium for about five months, while they grew strong enough to make it in the wild. To equip the baby seahorses for survival in the harbor, scientists provided special around-the-clock care, including nearly nonstop feeding.

“Seahorses can be quite difficult to look after in the captive environment. They can be quite sensitive,” Brennan tells the Guardian’s Catie McLeod. “They don’t have a stomach, so they have to eat constantly. So, we provided them with live shrimp almost constantly.”

It's been a week since we released ~380 endangered White's seahorses.

We've been delighted to see so much coverage in the media around Australia & the world.

We are also thrilled to receive plentiful submissions to the iNaturalist project.

Thank you citizen scientists! pic.twitter.com/6rAt4lUqgR

— Sydney Institute of Marine Science (@SydneyMarine) July 25, 2023

The recent release marks the fifth time captive-bred White’s seahorses have been introduced to the wild in the area, per the Australian Broadcasting Corporation. This latest attempt boasted the best survival rate to date—about 90 percent of the babies survived the transfer to the harbor.

Seahorses prefer calm, temperate waters and generally live in coral reefs, seagrass beds and estuaries. As predators that eat mostly miniscule sea creatures like krill, fish larvae and other small organisms—and as prey to crabs and other larger sea creatures—they play a crucial role in the marine ecosystems they inhabit.

Tagging of White's seahorse

Watch on

The Sydney Seahorse Project is a collaboration between the Sydney Institute of Marine Science, the University of Technology Sydney and the New South Wales Department of Primary Industries.

Before releasing the seahorses into the hotels, scientists injected miniature tags under the animals’ skin. This will allow them to track and monitor these creatures in the wild for the upcoming year.

“Hopefully, we’ll see population recovery so it’s no longer an endangered species,” Harasti tells the Australian Broadcasting Corporation.

Molly Enking | READ MORE

Molly Enking is a writer, editor and producer based in Brooklyn, New York. Her work can be found in Wired, Rolling Stone, PBS NewsHour, Grist, Gothamist and others. She covers health disparities, space, the environment, scientific discoveries and oddities, food and travel, as well as how art, pop culture and history impact the way we view the world.