In the 1990s, a school of bull sharks washed into the freshwater lake of Carbrook Golf Club in Australia due to flooding and became stranded for an extended period.
A new study published in the journal Marine and Fishery Sciences documents the unique population of bull sharks living in the artificial lake at Carbrook Golf Club, Australia, for nearly two decades, as reported by Live Science on September 27.
Bull sharks (Carcharhinus leucas) are unusual in that they can thrive in freshwater environments. This species is found in many rivers around the world. Although living in freshwater is typically temporary, they sometimes become stranded in these environments for long periods and continue to thrive.
Unlike many other shark species, bull sharks can live in freshwater environments like rivers. (Photo: ullstein bild/Getty).
The shark school at the golf course likely drifted inland during flooding. Carbrook Golf Club is located southeast of Brisbane, adjacent to the Logan and Albert Rivers. Summer storms sometimes bring heavy rainfall that overflows the riverbanks, flooding the surrounding areas. The golf course is less than 10 km from the coast, placing it within the range of freshwater where bull sharks can inhabit.
The sharks arrived in the lake around 1991 – 1996. During that time, three floods caused the water to overflow the riverbanks and inundate the land, bringing the sharks with it. When the floodwaters receded, they became trapped in the lake.
The shark school was first discovered in 1996. Although the lake is relatively small and shallow—approximately 700 meters long and 380 meters deep—there are no official statistics on the number of sharks present. However, they are frequently seen close to the shore. Their presence has been welcomed by the golf course management, and bull sharks have become a mascot for the venue.
According to observational reports, the bull sharks may have been small when they became stranded, but they eventually grew to lengths of up to 3 meters. Their feeding habits have not been extensively studied, but the species likely relied on an abundant food supply from fish that entered the lake during flooding events, such as flathead mullet (Mugil cephalus), Indian-Pacific tarpon (Megalops cyprinoides), silver snapper (Lutjanus argentimaculatus), and yellowfin bream (Acanthopagrus australis).
“If the sharks are able to find the food they need, living in low-salinity environments can be very beneficial due to fewer predators. Younger individuals in some ‘shark nurseries’ can survive for many years in freshwater, so it’s not surprising that they survived, as long as there was plenty of food,” said Michael Heithaus, a shark biologist at Florida International University.
The last sighting of bull sharks in the lake was in 2015. The flooding in 2013 likely allowed some to escape into nearby rivers, while others may have died and sunk. Golf course staff reported recovering the carcass of one shark while it was still alive in the lake.
Currently, the golf course lake appears to no longer have sharks, but this strange story showcases their adaptability and resilience in freshwater environments. The research team stated that this represents the longest recorded instance of bull sharks living continuously in low-salinity environments.
