Scientists in Sydney Harbour have successfully completed the world’s largest ever seahorse release. 

Approximately 380 seahorses, bred in captivity by the Sydney Institute of Marine Science (SIMS), have been reintroduced into their natural habitat at Chowder Bay on the north side of the harbour.

The White's seahorse, which was declared endangered in 2020, has suffered a significant decline due to habitat destruction and repeated rain events in Sydney Harbour and Port Stephens. 

The aim of the latest release, and planned future releases, is to contribute to the recovery and restocking of the wild populations.

After months of raising baby seahorses in captivity, scientists carefully descended to the ocean floor, carrying the seahorse fry in large plastic bags. They then placed the seahorses in their preferred habitats, including natural seagrass or specially designed “seahorse hotels”. 

It was the fifth release of White's seahorses bred in captivity in Sydney or Port Stephens, and appears to have had the highest survival rate, according to SIMS general manager Brett Fenton. 

“We have high expectations that we'll see the animals thrive over the next 12 months,” Mr Fenton told the ABC.