The language barrier between sharks and humans means the big fish don’t always appreciate that the scientists and researchers poking, prodding, and conducting tests or procedures on them in the water are actually trying to help save their species. That was the case in December 2024 for Dr. Mark Erdmann, as he tried to manoeuvre a male Indo-Pacific leopard shark in a state of ‘tonic immobility’ up to the ocean surface in Australia to attach an acoustic tag.

“One of the bigger males struggled significantly, so I had to use my body to push it into the sling on the side of the boat,” says Erdmann, senior scientist at Conservation International and Executive Director of ReShark.

“Consequently, I was pinned under the shark during the whole surgical procedure – the big issue was maintaining my breathing through my snorkel as waves broke over my head. The procedure was finished in about 10 minutes and we started to lower the sling to release the shark, at which point it promptly turned over and bit my calf. It was exceptionally painful, like someone had tightened a vice around the meat of my calf muscle and was trying to rip it off. The vets managed to pry the jaws open and release me (and the shark), but it was painful to walk for the next two weeks.”

A little gratitude from the shark wouldn’t have gone amiss. Erdmann was one of 15 international scientists, conservationists, and vets who took part in what was named the Great Australian Stegostoma Semen Expedition (GASSE), which set out to achieve a ‘world first’ in conservation: collecting semen from wild sharks.

From December 7-14, 2024, the team used innovative techniques to collect semen from Indo-Pacific leopard shark males (also known as zebra sharks) aggregating off North Stradbroke Island off Brisbane, Australia, with the intention of using it for artificial inseminations of female leopard sharks in aquariums across Australia and in Singapore, subsequently helping restore populations in the wild, including in Raja Ampat, Indonesia, where ReShark primarily operate.

The procedure for collecting semen from leopard sharks underwater was pioneered by Dr Paolo Martelli, Director of Veterinary Services at Ocean Park Hong Kong. “Leopard sharks have an interesting response to having their tail grasped, which puts them into a ‘tonic immobility’,” explains Martelli, GASSE’s primary vet.

“They use this to subdue females when mating but it also works on males, so we gently grasp the very end of the tail and roll them over onto their backs. We can keep them in this position for tens of minutes, which enables the procedure to be undertaken.”

Once immobilised, an Fr5 or Fr8 feeding tube, measuring 40 centimetres, is inserted (typically around 7-15 centimetres) into the shark’s seminal papillae to draw semen into a syringe barrel. The technique had only ever been used previously in an aquarium setting, usually taking around 10-15 minutes. But working with sexually mature adult leopard sharks (Stegostoma tigrinum) in the wild is a different kettle of fish.

“The biggest concern is always the weather and environmental conditions,” says Dr. Christine Dudgeon, Senior Research Fellow at University of Queensland and Biopixel Oceans Foundation, who led the GASSE expedition. “If it’s too rough, or there are strong currents, cold upwellings or dirty water after rain, the animals will often move away from the aggregation site. We were very lucky as the weather held out for us.”

“The first shark is always the most exciting because this is truly the very first time this has been done,” Dudgeon adds. “Watching the process of the sperm collection and blood collection using scuba was amazing. I was holding the tail for that, so I had an excellent view.”