Many shark species in Australia exhibit migration patterns similar to humans, moving northward in winter to avoid cold and southward in summer to escape excessive heat. This behavior is crucial for ectothermic sharks and rays that rely on external temperatures for body regulation.
Marine ecologist Jessica Meeuwig from the University of Western Australia stated that research indicates marine megafauna are moving towards the Earth's poles as oceans warm. For Australia, this signifies a southward shift. This global phenomenon requires consideration for animal management and human interactions.
Bull Shark Observations
Bull sharks, typically found in tropical settings and waters above 22°C, are present from Western Australia's southwest to southern New South Wales (NSW). While often found north of Sydney, some venture into the Paramatta River during summer.
Nicolas Lubitz, an ecologist at James Cook University, tracks bull sharks on the east coast. Resident sharks in Cape York stay year-round, while others are seasonal migrants, traveling to southern NSW/Sydney in summer and returning to Cape York in winter.
Research from five years prior predicted a three-month increase in suitable bull shark habitat in NSW by 2030. Lubitz's own 15-year study found migrating bull sharks increased their summer stays in Sydney by one day annually, totaling an extra 15 days by 2024 compared to 2009. This indicates extended stays, not necessarily an increase in overall shark numbers. Bull shark nurseries may also be expanding south, with increasing reports of pups in the Hawkesbury River, historically south of the Hunter River limit.
Tiger Shark Distribution
Tiger sharks are found across similar Australian regions. A study from 2002 to 2020 indicated female sharks tend to remain in Queensland waters, while juvenile males range further south towards Victoria. Adult male patterns are less clear due to limited tagging.
Study lead author Yuri Niella reported that modelling suggests tiger shark range could extend to Tasmania's east coast by 2030, though detections have already occurred there. Niella noted that these sharks respond to water temperature, not geographic boundaries. Future distribution may also depend on changes in prey distribution, such as sea turtles moving southwards into NSW.
White Shark Habitat Changes
White sharks are regionally endothermic, capable of generating warm blood. They inhabit cooler southern waters from northwest WA to southern Queensland. Juvenile and sub-adult white sharks on the east coast travel thousands of kilometers annually, preferring waters between 16°C and 24°C, typically within 20 kilometers of the coast.
These sharks spend summers in south-west Victoria and near the NSW-Victoria border, moving north to Queensland and northern NSW in winter. Marine ecologist Adrienne Gooden's study suggests a potential loss of wintering habitat in coming decades due to ocean warming. This could lead to a compression of habitat, making regions like the Twofold Shelf more critical for young sharks and potentially shifting their abundance and distribution along the NSW coast.
Impacts on Cold-Water Species
While species like scalloped hammerheads, zebra sharks, and manta rays are also moving south, the implications for cold-water species along Australia's south coast are different, as they cannot simply move further south to Antarctica.
Marine scientist Louisa Graf's study indicated a potential decline in suitable habitat for Victorian shark and ray species by 2090 under moderate warming scenarios. This could result in an overall drop in fiddle ray abundance, though some species like gummy sharks might see an increase. Graf suggested that marine protected areas could serve as refuge sites in the future, emphasizing the need for more information to understand the full impacts of ocean warming.