In the 1990s, a school of bull sharks washed ashore in the freshwater lake of the Carbrook golf course in Australia due to flooding and became trapped for an extended period.
Unlike many other shark species, bull sharks can live in freshwater environments such as rivers. Photo: ullstein bild/Getty
A new study published in the journal Marine and Fishery Sciences chronicles the story of a unique population of bull sharks that lived in a man-made lake on the Carbrook golf course in Australia for about two decades, Live Science reported on September 27.
Bull sharks ( Carcharhinus leucas ) are unusual in that they can live in freshwater environments. These animals are found in many rivers around the world . While living in freshwater is usually only temporary, they sometimes become trapped in this environment for extended periods and still thrive.
The sharks at the golf course may have been swept inland during the flooding. Carbrook Golf Course is located southeast of Brisbane, right next to the Logan and Albert rivers. Summer storms sometimes bring heavy rains that overflow the riverbanks, flooding the surrounding floodplains. The golf course is less than 10 km from the coast, placing it within the freshwater habitat of bull sharks.
The sharks arrived at the lake between approximately 1991 and 1996. During that time, there were three floods that caused the river to overflow its banks, inundating the land and carrying the sharks with it. When the floodwaters receded, they were trapped in the lake.
The sharks were first spotted in 1996. Although the lake is relatively small and shallow—about 700 meters long and 380 meters deep—there are no official statistics on the shark population. However, they are frequently seen near the shore. Their presence is welcomed by the golf course management, and the bull shark has become the mascot of the place.
According to observational reports, the bull sharks may have been small when they became trapped but eventually grew to 3 meters in length. Their feeding habits have not been thoroughly studied, but it is likely that introduced species during floods, such as the flathead grey mullet ( Mugil cephalus ), Indo- Pacific scad ( Megalops cyprinoides ), silver snapper ( Lutjanus argentimaculatus ), and yellowfin snapper ( Acanthopagrus australis ), are abundant food sources.
"If sharks can get the food they need, then living in low-salinity environments can be very good because there are fewer predators. The juveniles in some 'shark nurseries' can live for years in freshwater, so it's not surprising that they survive, as long as there's plenty of food," said Michael Heithaus, a shark biologist at Florida International University.
Bull sharks were last seen in the lake in 2015. The 2013 floods likely helped some escape into nearby rivers, while others may have died and drowned. Golf course staff once recovered the carcass of a shark while it was still alive from the lake.
The golf course lake currently appears to be free of sharks, but this unusual story demonstrates their ability to adapt to and tolerate freshwater environments. The research team stated that this is the longest recorded instance of a bull shark continuously surviving in a low-salinity environment.
Thu Thao (According to Live Science )
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