Scientists collect shark semen by hypnosis to save species from extinction
Australian marine scientists are using an inventive (and somewhat unusual) way to collect semen from wild male leopard sharks to boost their population and genetic diversity through artificial insemination.
The method, known as “tonic immobility,” involves turning sharks on their backs, inducing a temporary trance-like state that makes it safer and easier to gather reproductive materials.
“Never thought I’d be getting this intimate with sharks underwater,” jokes Dr. Christine Dudgeon of the University of the Sunshine Coast on a social media post, describing the team’s experiences during their December expedition.
Tonic immobility in action
Tonic immobility is observed in vertebrates and invertebrates, sometimes called “animal hypnosis.” In sharks, the reflex can be triggered by gently stimulating tiny sensory pores on their snouts. Once immobilized, the sharks lie motionless, allowing researchers to collect semen and blood samples safely.
“Our five-person team could syringe out semen and blood samples from male sharks underwater in the wild using ‘tonic immobility,’ where sharks go into a sleep-state on their backs,” explains Dudgeon.
The expedition, aptly named the Great Australian Stegostoma Semen Expedition (GASSE), focused on leopard sharks (Stegostoma tigrinum), also known as zebra sharks, because younger individuals have stripes that later develop into spots.
These sharks, which can exceed two meters in length, frequent coral reefs and sandy flats in the Indo-Pacific region. Despite their size, leopard sharks are considered harmless to humans, spending most of their time resting on the ocean floor and becoming active at night to feed on small fish and invertebrates.
In addition to collecting semen samples off North Stradbroke Island near Brisbane, Dudgeon’s team successfully used the same technique to inseminate female leopard sharks in aquariums across Australia and Singapore. If the resulting eggs are deemed fertile, they will be sent to the Raja Ampat Islands off West Papua for hatching. Hopefully, these juveniles will help replenish threatened leopard shark populations in protected waters.
Preserving an endangered species
The International Union for Conservation of Nature (IUCN) lists Leopard sharks as endangered. While populations in Australia remain relatively stable, since local fisheries do not typically harvest these sharks, other countries have seen steep declines.
Overfishing for fins, meat, and their exceptionally tough skin has fragmented global populations. Some estimates suggest that the population of the Indian Ocean–Southeast Asian population has dropped by at least 50 percent in the past half-century.
“We hope this marine reproduction technique will be a game-changer for international projects aiming to replenish the Stegostoma species globally,” says Dudgeon. “Particularly in areas such as Indonesia, where it is in danger of becoming extinct.”
Looking ahead, Dudgeon and her colleagues plan to dive off northern New South Wales in late March to gather more semen samples. They will also fit male sharks with acoustic tags to track their movements using a network of marine receivers, a step designed to inform conservation strategies further.
“We can now follow these sharks’ movements … to further inform conservation work for this ambitious restocking project,” Dudgeon adds. If successful, this approach will not only deepen our understanding of leopard shark behavior and biology. Still, it could also serve as a critical measure for rescuing an iconic species from the brink of extinction, one gentle belly rub at a time.
Source: Interesting Engineering
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Scientists collect shark semen by hypnosis to save species from extinction