Mimicking the ink emitted by bioluminescent cephalopod mollusks could be an innovative way to protect both
sharks and humans.
Researchers from University College Dublin have found that the murky ink of the medicinal cuttlefish (Sepia officinalis) can deter sharks, preventing them from effectively hunting in areas where people often swim. By creating complex models of the olfactory systems of different species of sharks, the scientists found that bioluminescent secretions of cephalopods can suppress the hypersensitive perception of odors in these marine predators.
These findings open new perspectives for the development of environmentally friendly repellents that can limit shark activity near beaches and fishing grounds without harming marine ecosystems. The findings are detailed in a scientific paper recently published in the journal G3: Genes, Genomes, Genetics.
"In understanding how predatory species such as cuttlefish have managed to adapt and exploit the weaknesses of larger marine predators such as sharks, we are not only advancing our knowledge of marine ecosystem dynamics, but also opening up new perspectives for developing conservation strategies based on the mechanisms of nature itself," notes one of the study's authors, biologist Colleen Lawless.
Sharks are top predators, largely due to their six highly developed senses: perception of electromagnetic fields, sight, touch, taste, hearing, and smell.
Many shark species can smell blood from about half a kilometer away, and once they have found the source of the blood, they can use their impressive jaws and muscles to tear their prey apart. However, their remarkable sense of smell can be a weakness.
In a new study, scientists created in vitro three-dimensional models of the olfactory system of two species of sharks - the Japanese catshark (Scyliorhinus torazame) and the
big white (Carcharodon carcharias). In testing the effects of cuttlefish ink, the team found that melanin, its key component, has a unique molecular structure that allows it to interact with the sharks' olfactory receptors.
These connections disrupt the ability of predators to pick up odors, disorienting them and encouraging them to avoid areas where ink has been sprayed. Moreover, this effect probably applies to most shark species, as their olfactory receptors are similar in structure.
According to the research team, the effectiveness of cuttlefish ink as a natural shark repellent has applications in conservation, marine resource management and human-shark coexistence.
Some of the modern non-lethal methods of deterring sharks from beaches are gill nets (a net is set vertically right in the path of the fish, which tries to swim through the net, but gets tangled in the mesh, getting stuck by its head, gills or fins, which does not allow it to get back out) and barrier lines.
These invasive fishing methods result in the accidental entanglement of not only large sharks, but also many other marine creatures, including rays, dolphins, sea turtles and even baby whales. This creates serious ecological problems, upsetting the balance of marine ecosystems.
"Our findings could form the basis for the development of safe and selective repellents that could be applied near beaches, aquaculture farms and fishing areas to minimize accidental shark-human encounters," explains Lawless. "In addition, these results may contribute to better management of shark movements in ecologically sensitive areas."
Synthetic analogs of the compounds found in cuttlefish ink can be reproduced in the laboratory and sprayed in the water to deter sharks from danger zones, he said. This could play an important role in protecting endangered species by creating protective barriers in active fishing grounds or polluted waters, reducing risks to both sharks and the environment.