Tiger sharks, dugongs and sea turtles: a triangle of fear in Shark Bay
Shark Bay (Gathaagudu) is an Australian UNESCO World Heritage Site that supports endangered marine megafauna, including dugongs and loggerhead and green turtles. The bay also sustains 28 shark species, with the tiger shark as the apex predator. But declines in dugongs and sea turtles after marine heat waves have Olga worried. For Shark Bay the risk of impact from climate change is ‘catastrophic’ and she wants to understand how changes in prey availability will affect predator behaviour and overall ecosystem health. Olga is exploring trophic connections between tiger sharks and turtles, dugongs and other potential prey to aid the conservation of this special place.
Olga M. Azevedo
I was born and raised in a village in the north of Portugal that is connected to the Atlantic Ocean via the Coura and Minho rivers, to the Serra d’Arga mountains, to the Veiga plains and to Spain. I like to call it my little piece of heaven, my hidden paradise. It’s a small village, with fewer than 400 inhabitants, and I was always fascinated by the nature all around, the animals and the humans, and the connections between them all. Curiously, I feared the ocean and its big waves, yet as a small child I used to...
How much are tiger sharks feeding on threatened dugongs and turtles in Shark Bay, Australia?
To quantify the extent to which tiger sharks feed on threatened dugongs and turtles in Shark Bay, Australia.
By quantifying the reliance of tiger sharks on endangered megafauna like turtles and dugongs as prey, we can understand their impact on these threatened species. Since dugong and turtle populations have declined after a severe marine heat wave and Shark Bay is at ‘catastrophic risk’ from climate change, knowing the dietary habits of sharks helps us understand how shifts in prey availability affect predator behaviour and ecosystem health, ultimately aiding the conservation of this unique and vulnerable marine environment.
Shark Bay (Gathaagudu), located on Australia’s western coast, is a UNESCO World Heritage Site renowned for its expansive and diverse sea-grass beds, which are among the largest globally. These sea-grass meadows support endangered marine megafauna, including dugongs and sea turtles (loggerhead and green turtles). Shark Bay harbours more than 10% of the world’s dugongs – essential to the health of the sea-grass ecosystem – and hosts Australia’s largest loggerhead nesting colony. The bay also sustains 28 shark species, with tiger sharks as the apex predators that play a crucial role in regulating the marine ecosystem.
However, Shark Bay is under significant threat from climate change. In 2011, a severe marine heat wave caused widespread die-off of sea grass, leading to sharp declines in dugong (67%) and green turtle (39%) populations. Tiger shark catch rates remained stable, however, suggesting a possible shift in predator–prey dynamics, as these sharks are likely to prey on the declining megafauna.
Current knowledge gaps include the present diet of tiger sharks and the extent to which they prey on threatened species. Understanding how changes in prey availability affect predator behaviour and overall ecosystem health is crucial. As Shark Bay’s fragile ecosystem, which has been classified at ‘catastrophic risk’ from climate change, continues to adapt to ongoing climate pressures, unravelling these interactions is essential for protecting its vulnerable species and aiding their recovery.
- To explore trophic connections between tiger sharks, turtles, dugongs and other potential prey through dietary analysis.
- To analyse sharks’ energy sources to understand the impact of their predation on threatened dugongs and turtles.
- To compare trophic positions and isotopic niches among and within species to reveal inter- and intra-specific preferences.
- To reveal the food web structure, highlighting the roles of dugongs and turtles and their interactions with tiger sharks.