Scientists “Hypnotize” Sharks To Harvest Semen And Successfully Inseminate Females

The marine scientists are using a special and slightly weird method, known as “tonic immobility”, to effectively hypnotize male leopard sharks. It’s kind of basic in principle, though probably tricky to master in real life: essentially, the sharks are induced by gently stimulating the sensory pores on their snouts. 

The animals can then be turned upside down, which seems to disorientate them, causing them to become easier to handle. As they enter the state, their muscles relax, and their breathing becomes deeper and more rhythmic.

It is completely safe for the sharks, and once they are released from the state, they quickly revert to normal.

Sharks are not the only animals to enter tonic immobility. The behavior has also been seen in other species – including rays and birds – though the methods for inducing it do not necessarily involve turning them upside down, such as in the case of sharks. It is not currently known why this state occurs, but it may have something to do with mating in some species while being a defensive response in others.

In the case of sharks, inducing tonic immobility allows researchers to collect samples. “It meant that our five-person team could syringe out semen and blood samples from male sharks underwater in the wild,” said leopard shark researcher Dr Christine Dudgeon in a statement.

“Never thought I’d be getting this intimate with sharks underwater,” Dudgeon jested in a Facebook showing photos of the team in action.

But why are these researchers…milking…these males? Well, Indo-Pacific leopard sharks (Stegostoma tigrinum, known as zebra sharks elsewhere due to their pups having stripes that develop into spots) are currently categorized as endangered on the IUCN Red List of Threatened Species.

So, Dudgeon and her colleagues from across the world who are part of the Great Australian Stegostoma Semen Expedition are attempting to help the species by artificially inseminating female leopard sharks at Sea World Gold Coast, SEA LIFE Sydney Aquarium, and Resorts World Sentosa in Singapore.

“We hope this marine reproduction technique will be a game-changer for international projects aiming to replenish the Stegostoma species globally, particularly in areas such as Indonesia where it is in danger of becoming extinct,” said Dudgeon.

The team will also be keeping a close eye on the DNA of any pups that come from this work; there is documented evidence of the species being able to lay healthy eggs without fertilization from males. Dudgeon witnessed this form of “virgin birth” – known as parthenogenesis – in 2016 while studying a shark that hatched three pups in a Townsville aquarium, finding that it seems to happen more often in global research.

 

“Once these eggs are laid and veterinarians have determined they are fertile, they will be sent to our partners in the Raja Ampat Islands, off West Papua, until they hatch into juveniles that will hopefully help restock those protected waters,” Dudgeon added.

Alongside collecting semen for artificial insemination, the team also brought some sharks to the surface to insert acoustic tags.

“We can now follow these sharks’ movements via a network of marine acoustic receivers to further inform conservation work for this ambitious restocking project,” said Dudgeon.