Australian Sharks Follow “Gray Nomad” Pattern South as Oceans Warm
Table of Contents
As Australia’s oceans rapidly warm, shark populations are mirroring teh migration patterns of retirees, heading south to escape rising temperatures, raising concerns about the future of marine ecosystems.
Australia’s shark species, like many marine animals, exhibit a seasonal migration driven by temperature.traditionally, these creatures journey northward in winter to avoid the cold and return south in summer to escape excessive heat. this behavior is particularly crucial for ectothermic – or “cold-blooded” – sharks and rays, which rely on external temperatures to regulate their body temperature. But with climate change accelerating ocean warming, this established pattern is being disrupted, forcing sharks to seek cooler waters further south, and prompting scientists to consider the implications for both marine life and human interactions.
Bull Sharks Extend Summer Stays in Sydney
Bull sharks (Carcharhinus leucas), commonly found in coastal waters and rivers from Western Australia to New South wales, are already demonstrating a shift in behavior. While generally preferring warmer, tropical settings with temperatures above 22°C, these sharks are increasingly extending their summer stays in more southern regions.
“They sort of do this whole thing where they go to southern NSW, Sydney area, in the summer and then head back north for winter,” explains Dr.Rob Townsend, a marine biologist at the University of Exeter. “But we’re seeing them hang around for longer and longer each year.They’re not going as far north, and we’re seeing more juvenile males range further south, towards Victoria.
Modeling suggests the tiger shark’s range will expand to Tasmania’s east coast by 2030. Though, this prediction is already being observed. “We last year serviced our line down in maria Island and for the first time in 20 years of this programme we got tiger sharks detected,” stated a science officer at the IMOS Animal Tracking Facility in Sydney.”These guys are expanding their distribution range in face of climate change.The reality is these guys, they don’t really know it’s Tassie, they know the water is warm enough.”
This southward shift could also be linked to changes in prey distribution, with sea turtles reportedly moving south into NSW waters.
White Shark Habitat Faces Compression
Unlike bull and tiger sharks, white sharks (Carcharodon carcharias) are regionally endothermic, meaning they can generate and retain some body heat. However, even these adaptable predators are feeling the effects of warming oceans. Juvenile and sub-adult white sharks travel thousands of kilometers annually, favoring waters between 16 and 24°C, particularly around south-west Victoria’s Corner Inlet and the Twofold Shelf near the NSW-Victoria border in summer, and shifting north towards queensland and northern NSW in winter.
A marine ecologist from Southern Cross University warned of a potential “compression of habitat” for white sharks, as warming waters reduce their wintering grounds. “So it is likely that we will see a compression of habitat where they can’t move as far north, but they also are not getting increases in available habitat in that southern region.” This could make the Twofold shelf region increasingly importent for young sharks, potentially leading to shifts in their distribution along the NSW coast.
The Fate of Cold-Water Species
While many species are adapting by moving south, the future is less certain for cold-water species along Australia’s south coast that have limited options for further migration. A recent study led by a marine scientist at Deakin University suggests a potential decline in suitable habitat for Victorian shark and ray species by 2090 under a moderate warming scenario. This could lead to a drop in the abundance of fiddle rays, even though some species, like gummy sharks (Mustelus antarcticus), might experience a boost.
“Our research did indicate that marine protected areas may serve as potential refuge sites in the future,” the scientist noted. “More information is needed to really see or understand the full impacts of the ocean warming.”
The changing distribution of sharks underscores the urgent need for adaptive management strategies to protect both these vital marine predators and the ecosystems they inhabit.
