Scientists have uncovered a remarkable hunting strategy in the Mediterranean Sea: blue runner fish using sandbar sharks as cover to ambush prey.
Underwater footage from Italy’s Lampione island reveals the predatory fish 'shadowing' sharks for around 30 seconds before launching high-speed attacks.
By doing so, they catch prey off guard, increasing hunting success. This behaviour may also help the fish conserve energy and evade predators.
The findings, published in the journal Ecology, highlight the ecological role of shark aggregations, which are threatened by overfishing.
Blue runner ambush
Measuring up to 2.5 metres in length and weighing almost 100kgs, the sandbar shark is a medium-sized species of migratory shark that aggregates in the Mediterranean Sea every summer.
Whilst studying this enigmatic species around Lampione – a small, rocky isle between Sicily and Tunisia – researchers from the University of Edinburgh spotted a smaller fish species shadowing it.
They identified it as the blue runner, a fast-swimming predator that eats small fish.
Keen to find out why the blue runner was tailing the shark, the team deployed divers and remotely operated vehicles to film the behaviour, discovering something remarkable; the videos show 34 examples of blue runners using the cover of sharks to hunt smaller types of fish, such as damselfish.
During these attacks, prey noticed the blue runner’s approach roughly 10 per cent of the time. In contrast, when the fish hunted in packs (away from the sharks) their prey spotted them more than 95 per cent of the time. On these occasions, the prey was able to position itself into a defensive schooling formation, reducing the success of the attacks.
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As well as improving their chances of a successful hunt, the shadowing behaviour may protect blue runners from their own predators, the team says. The strategy also helps them conserve energy by swimming in a shark's slipstream.
“Understanding these dynamics enriches our knowledge of marine biodiversity and underscores the importance of conserving high-level predators, like sharks,” says Professor Fabio Badalamenti from the University of Edinburgh and CNR-IAS Palermo.
Dr Carlo Cattano, from the Stazione Zoologica Anton Dohrn, adds that “Lampione Island is one of only two known aggregation areas for the sandbar shark in the Mediterranean Sea. 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, led by the University of Edinburgh, involved researchers from Stazione Zoologica Anton Dohrn, the National Biodiversity Future Center, CNR-IAS and the University of Palermo.
Find out more about the study: To see and not be seen: Carangids hide behind sharks to prey on fish
Image and video credit: Desirée Grancagnolo
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