For 17 years, a group of six bull sharks have lived in a lake near the 14th hole at Carbrook Golf Course in Brisbane, Australia. Talk about having the ultimate water hazard during a round of golf! The lake was teeming with sharks, suggesting that species can live in low-salinity environments indefinitely.
In 1996, raging floods swept the group of young bull sharks from a nearby river into the 51-acre lake. When the waters finally receded, the sharks found themselves trapped in the lake and surrounded by golfers. The sharks would stay in the lake for the next 17 years, surviving off the large stock of fish. Club staff would occasionally drop a meat treat into the lake for the predators. (This sounds like the beginning of a “Lake Placid” ripoff!) One shark was illegally fished out of the lake, the others left during subsequent floods.
According to a new study, these sharks’ survival is more than a fluke. Peter Gausmann, a shark scientist and lecturer at Ruhr University Bocham in Germany, was part of this research team. The research suggests that the sharks at Carbrook demonstrate bull sharks ability to live in low-salinity aquatic environments indefinitely. The full findings of this research is published in the Marine and Fisheries Sciences journal.
Bull sharks are typically found in warm costal waters across the world. However, they are one of a few shark species that can survive in a range of salinities. Mature sharks range from 11 to 13 feet long and weigh up to 500 lbs. They can venture between saltwater and freshwater habitats, even brackish environments like rivers, estuaries, and lagoons. They are also responsible for dozens of fatal attacks on humans, thanks to this impressive adaptation.
Most sharks upon entering a freshwater habitat die, due to their internal salt levels becoming diluted. This is not the same case for bull sharks, whose special kidneys and rectal glands recycle and retain their salt levels. Freshwater and brackish environments allow for young bull sharks to grow without predation from larger sharks. Once mature, they head to the sea for larger prey and breeding opportunities. The Carbrook population never increased, proving bull sharks prefer to breed in saltwater.
While scientist know that bull sharks can live up to 30 years, no one knows how long they can live in freshwater. The Carbrook Gold Course sharks were in that lake near the 14th hole for 17 years. This suggests there is no upper limit as to how long they can live in low-salinity environments.