With the world's shark populations under threat, scientists say the best way to protect sharks is to understand how they benefit ocean environments, and then maximise the benefits they bring.
James Cook University's Adjunct Professor Colin Simpfendorfer is the co-author of a new paper looking at what sharks contribute to the ecosystems they inhabit.
He said rather than just being top predators, sharks perform a variety of roles.
"For example, the mere presence of large tiger sharks in Western Australia makes seagrass grazers such as green turtles and dugongs more wary and protects the seagrass from overgrazing.
"Reef sharks feed in offshore waters and bring nutrients back to the reef. Others move nutrients around at the base of the food chain. Sharks can also serve as food for other species and even as scratching posts for fish to remove parasites," said Professor Simpfendorfer.
He said oceanic shark abundance has plummeted by 71% in the past 50 years, with populations of the top five reef shark species depleted by 63% and catch rates of large coastal sharks in the Australian beach protection program declining by 90% since the 1960s.
"It's time to have a conversation about everything sharks are doing to maintain ocean health so we can better prioritise conservation efforts and have the biggest impact," said Simon Dedman, researcher at Florida International University (FIU) and lead author of the study.
The scientists evaluated global depletions of sharks, investigated their diverse ecological roles, and explored their past, present, and future roles.
"We looked at what roles are currently important, identified where population restorations may be particularly beneficial and evaluated policies that can support recovery," said Professor Simpfendorfer.
He said overfishing is the overwhelming force degrading sharks, but climate change, habitat loss and the blue economy (energy, mining, shipping, aquaculture), will further impact sharks and how they fit in the ecosystem.
"Finding a balance that protects the sharks most needed for healthy oceans is critical," said Professor Simpfendorfer.
Professor Mike Heithaus, study co-author and FIU marine ecologist, said policy must now focus on actions to rebuild populations and restore sharks' functional roles.
"That requires action to increase both spatial measures like Marine Protected Areas and fisheries management measures like catch/size limits and gear limitations. If people want healthy oceans, we need healthy shark populations."
