Can cuttlefish ink be “bear spray” against sharks?

Diving in the crystal-clear waters of the Red Sea or exploring the vibrant reefs of Australia is an unforgettable experience. But sharing the ocean with sharks can be a nerve-wracking thought, even for the most seasoned divers. What if there were a natural, non-lethal way to keep sharks at a safe distance? Recent research suggests that cuttlefish ink might be the answer. It is much needed: a recent tragic dive boat accident in the Red Sea that led to 11 deaths was prevented from being rescued quickly because of sharks in the area, according to witnesses.

Cuttlefish (Sepia officinalis) are known for their impressive camouflage skills and their ability to release a cloud of ink when threatened. This ink isn’t just a visual smokescreen—it also contains chemical compounds that can overwhelm a predator’s sense of smell. Sharks, in particular, rely heavily on their acute olfactory senses to navigate and hunt. The compounds in cuttlefish ink are thought to disorient sharks, making them less likely to approach the source of the scent.

Recent research from University College Dublin indicates that cuttlefish ink, particularly its primary component melanin, may serve as an effective shark deterrent. The study found that melanin can bind to shark olfactory receptors, potentially overwhelming their sense of smell and causing them to avoid areas where the ink is present.

“Understanding how prey species like cuttlefish have evolved to exploit specific vulnerabilities in predators like sharks enriches not only our understanding of marine ecosystems but provides inspiration for conservation tools rooted in natural processes,” said Colleen Lawless, a researcher in the study.

Modelling the three-dimensional structures of shark olfactory receptors by using genetic data from several shark species including the Great White Shark, Colleen and her colleagues Dr Graham Hughes and Dr John Finarelli discovered melanin possesses a molecular structure that lets it latch onto the smell receptors of these ocean predators, disrupting their sensory perception.

And because sharks generally share the same core set of smell receptors despite differences in lifestyle and habitat, the binding effect likely extends to all shark species, making it likely effective across most shark species.

This discovery suggests that deploying cuttlefish ink, or synthetic analogs, could create safe zones for divers by deterring sharks without harming them. Such an approach could enhance diver safety in regions like the Red Sea and Australian waters, known for frequent shark encounters. Additionally, this method offers a non-invasive alternative to traditional shark deterrents, which often pose risks to other marine life.

By releasing cuttlefish ink—or a synthetic version—into the water, it may be possible to create a safe zone that deters sharks. This approach could provide a protective barrier, allowing divers to observe marine life without posing a threat to themselves or the sharks.

Practical Applications and Challenges

For this idea to work in real-world scenarios, several challenges need to be addressed:

• Deployment Methods: The ink could be released from wearable devices, such as wristbands or diving suits equipped with small dispensers. Alternatively, underwater “ink bombs” could be deployed around high-risk areas. Or kept on hand during rescue dives. Divers from the Sea Story accident did not want to go on a rescue operation because of the number of sharks circling the floating wreck.
• Environmental Impact: It’s crucial to ensure that the ink doesn’t harm other marine species or disrupt the delicate ecosystem.
• Scalability and Production: Harvesting enough natural cuttlefish ink isn’t feasible, so researchers are exploring synthetic alternatives that mimic the chemical properties of the original ink.
• One of the most exciting aspects of this technology is its potential to protect both humans and sharks. By steering sharks away from popular diving sites, we reduce the chances of negative encounters that could lead to harmful outcomes for the sharks.

While promising, further research is necessary to develop practical applications and assess the environmental impact of widespread use of cuttlefish ink as a shark repellent.