Dugong. It's what's for dinner. 

This feeding show in the waters near Australia's Moreton Bay was caught on camera by two fishermen after they noticed frenzied bird activity overhead.

"Initially we could only see seagulls flying around the dugong and as we got closer we could see the two tiger sharks,” fisherman Bruce Flint told the Courier Mail community newspaper.  

Just like their sea-cow kin, the manatees, dugongs spend the majority of their time hoovering up seagrasses and other vegetation on the seabed. At first glance, it might be tough to tell the animals apart, but the secret lies in the tail: while manatees have a paddle-like tail, dugongs possess tail flukes, much like you'd see on a whale or dolphin. 

Combined with poor eyesight, their languid lifestyle makes dugongs relatively easy prey for tiger sharks, who are famously unfussy eaters. Across their range, these fearsome predators have been found with all sorts of tasty prey in their stomachs, from fish and crustaceans to turtles and sea snakes. 

“[The sharks] were huge against my 14ft tinnie [that's Aussie slang for "boat"]. One was definitely equal to or larger than our boat,” adds Flint.

The Moreton Bay area is home to around 1,000 dugongs, one of the biggest populations in Australian waters – but this is not the only spot Down Under where this kind of interaction has been observed. Across the Australian continent near Perth lies Shark Bay, where vast seagrass beds also sustain a large dugong population.

Research in Shark Bay has shown that its resident dugongs actually change their feeding behaviour based on the number of sharks in their territory, opting to dive deeper to avoid becoming lunch. Going fathoms below means they miss out on the most nutritious seagrass – but it also guarantees manoeuvrability for a quick getaway in case of an attack.

Despite their large and seemingly clumsy bodies, dugongs are capable of short bursts of surprising speed (up to 20 kilometres, or 12 miles, per hour), and while they can't sustain this for very long, it often allows them to dodge would-be predators. 

Hunters like the tiger shark are vital keystone species in tropical waters worldwide, including in Australia's Shark Bay. By feeding on seagrass-guzzlers like dugongs, the sharks indirectly keep these precious habitats from being overgrazed, helping to maintain a healthy ecosystem. 

Tiger Shark Mouth Related 2016 05 09


Top header image: Kevin Bryant, Flickr