In an exciting new revelation for marine scientists, evidence has been captured – for the first time – that some fish are using sharks as a means of ambushing their prey, by hiding behind them until their opportune moment to strike.

This previously unknown behaviour was discovered by a team of researchers, including those from the University of Edinburgh, studying sandbar sharks in the Mediterranean Sea.

For the first time in marine science history, underwater video footage captured by divers and remotely operated vehicles shows a type of small predatory fish called blue runners using the sharks for cover while they hunt.

While previous research has shown that some fish shadow sharks to remove parasites and hide from predators, this is the first time evidence has been captured of fish hiding behind them to ambush their prey.

Videos captured off the coast of Italy’s Lampione Island revealed 34 examples of blue runners using this hunting strategy. On each occasion, a single fish shadowed a shark for around 30 seconds before breaking off to launch high-speed attacks on smaller types of fish, such as damselfish.

Analysis of the footage suggests that the fish – which

usually hunt in small groups – are more likely to catch their prey off guard by shadowing sharks, increasing their chances of success, the team said.

When hiding behind a shark, prey only noticed a blue runner’s approach around 10% of the time. In contrast, when the fish hunted in packs their prey spotted them almost every time (more than 95% of attacks) and got into a defensive schooling formation.

The team has suggested that as well as improving their chances of a successful hunt, the shadowing behaviour may protect blue runners from their own predators and help them conserve energy by swimming in sharks’ slipstream.

“This unique interaction emphasises the ecological importance of the few remaining shark aggregations, which can influence the structure and function of ecosystems,” said Dr Carlo Cattano, of the Stazione Zoologica Anton Dohrn, a member of the research team behind the study.

The research is based on multi-year observations around Lampione Island, where a rare clustering – known as an aggregation – of sandbar sharks occurs every summer.

“Lampione Island is one of only two known aggregation areas for the sandbar shark in the Mediterranean Sea,” continued Dr Cattano. “The ongoing decline in large shark populations due to overfishing could jeopardise associations like these, which could have knock-on effects on other species.”

The study, published in the journal Ecology, was supported by the Blue Marine Foundation and National Geographic Society. Alongside researchers from Stazione Zoologica Anton Dohrn, it also included those from the National Biodiversity Future Center, CNR-IAS and the University of Palermo.

Professor Fabio Badalamenti, of the University of Edinburgh and CNR-IAS Palermo, said: “This study highlights how interactions between species can drive alternative hunting tactics in marine ecosystems. Understanding these dynamics enriches our knowledge of marine biodiversity and underscores the importance of conserving high-level predators, like sharks.”

Click here for more from the Oceanographic Newsroom.