For nearly two decades, Carbrook Golf Club near Brisbane, Australia, has had its biggest water hazard: a lake full of bull sharks.
It all started in 1996, when strong floods swept six young bull sharks from a nearby river into a 20-hectare lake near the 14th hole of the golf course. When the waters receded, the sharks were trapped, surrounded by grassy hills and curious golfers.
The sharks spent 17 years in the lake, supporting themselves on their large fish supply and the occasional meat treat provided by club staff. One shark was illegally caught, while the others disappeared in subsequent floods.
Sharks, according to a new study, are more than a mere fluke along the sports field. In research published last month in the journal Marine and Fisheries Science, Peter Gausmann, a shark scientist and professor at Ruhr University Bochum in Germany, said members of the Carbrook cartilaginous club demonstrate that bull sharks can live indefinitely in aquatic environments. low salinity.
Bull sharks can be found in warm coastal waters around the world. These robust sharks can reach 3 to 4 meters in length and weigh more than 250 kilograms. They are one of the few shark species capable of tolerating a wide range of salinities, a characteristic that allows them to venture into fresh and brackish water habitats, such as rivers, estuaries and lagoons.
Unfortunately, this impressive adaptability often places sharks in close proximity to humans, one of the many reasons why bull sharks are responsible for dozens of documented fatal attacks on humans.
If most sharks entered a freshwater environment, their internal salt levels would be diluted and they would die. But bull sharks have specially adapted kidneys and rectal glands that work together to recycle and retain salt in their bodies.
Freshwater and brackish water habitats provide young bull sharks with a place to grow up without the threat of predation by larger sharks. Once they reach maturity, however, bull sharks often head out to sea, where there is larger prey and more opportunities to reproduce. The fact that the Carbrook shark population did not grow during its time on the golf course offered further evidence that the species prefers to breed in saltier environments.
Although scientists have long known that bull sharks have the means to move between freshwater and saltwater environments, no one knows whether these sharks could spend their entire lives in freshwater.
Research suggests that bull sharks can live for about 30 years, and Carbrook’s group survived in the golf course lake for 17. This suggests there is “no upper limit” to how long they can spend in low-lying environments. salinity, said Vincent Raoult, a postdoctoral researcher at Deakin University in Australia who was not involved in the new study.
“I think a lot of people would be scared to know that there could be bull sharks in their local lake, but the fact is it’s amazing that there are animals capable of doing this,” Raoult said.
While the idea of sharing a lake with bull sharks might be scary to some, golfers loved the opportunity, said Scott Wagstaff, general manager of Carbrook Golf Club.
“Every member here loves sharks,” Wagstaff said.
When the sharks were still at the club, he and other employees threw pieces of meat into the water and were amazed at the way the sharks devoured the food with their terrible jaws. “I saw them jump completely out of the water and spin as they dove. It was really cool,” Wagstaff said.
Extreme flooding like the ones that washed sharks in and out of Carbrook Golf Club is becoming more common, and more bull sharks could end up abandoned in lakes and lagoons. While it’s highly unlikely you’ll find a bull shark in your local swimming pool, Gausmann recommends avoiding water bodies recently affected by flooding.
“You should never bathe in stagnant reservoirs of water that were once connected to the sea. You never know if sharks live there,” he said, although people in urban areas need not worry as urban flood waters are plentiful. often too toxic to support marine life.
And there’s another lesson to be learned, as shark sightings and occasional attacks on human swimmers provoke fearful reactions in some places.
“If this paper has shown anything, it’s that it’s possible to live side by side with sharks,” said Leonardo Guida, a shark scientist at the Australian Marine Conservation Society.
Translated by Luiz Roberto M. Gonçalves