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Four people were bitten go through shark within two days new south walesthree of which are located in Sydney Harbour. The two are in critical condition.
It’s unclear what species of shark caused this condition. But some of these incidents may involve the extremely adaptable bull shark (white shark). This unique fish can tolerate a wide range of water salinities, from the ocean to saltwater estuaries and even freshwater rivers.
Bull sharks were discovered early in Australian waters warmingranging from southwest to west Australiaall the way around the northern tip region and along the east coast to the New South Wales and Victoria border.
Bull shark activity in Sydney Harbor been studied For several years. Their presence is more likely in the summer when seawater warms. But they stayed longer than before. Last year, researchers found that bull sharks spend an extra day each year in their summer habitats (shallower coastal waters, estuaries and rivers) on average as climate change causes ocean temperatures to rise.
Record-breaking rain in Sydney has flushed huge amounts of nutrient-rich water from farms and wastewater treatment plants into river systems, including harbours. This loss of nutrients attracts more prey, such as baitfish and larger fish, which in turn attracts larger predators, such as sharks. Rain also makes harbor waters more turbid, meaning bull sharks rely more on hearing and electroreception than sight to find food sources. This can lead to bites due to mistaken identity.
Although human activity in the water (noise and movement) can attract sharks, humans are not a food source for bull sharks. Almost all encounters and negative interactions with these sharks come from From an exploratory bite. Unfortunately, for those affected, the bites can be very serious.
What could be behind these events?
Bull sharks are unique among sharks in that they can tolerate fresh, salt, and salt water. Most other shark species do not use estuaries or rivers as part of their range or life cycle. This ability to tolerate and adapt to different salinity levels is one of the reasons bull sharks are found in coastal waters and river systems, including estuaries, around the world.
Once mature, female bull sharks return to their home rivers to give birth to their pups. Newborns are small replicas of adults. As they grow, juvenile and sub-adult bull sharks move along river systems and tend to live lower in estuaries for the first five years of their lives to avoid larger predators. During that time, they opportunistically hunt a range of prey in order to grow larger before entering the open ocean.
Bull sharks are very opportunistic predators. Scientists have found a variety of things in bull sharks’ stomachs, such as wood, metal and other inorganic matter, even though fish are their preferred prey.
Water in estuaries and ports tends to be turbider than in the open ocean because rivers often carry large amounts of sediment and nutrients. This means bull sharks must rely on senses other than vision, such as sound that travels well underwater, smell, and their ability to sense weak electric fields caused by biological movement at close range. Many shark bites may be due to bull sharks’ habit of opportunistically biting people in case it might be food.
A surge of rain last week made Sydney Harbor darker and more nutrient-rich, attracting baitfish and the predators that follow them.
Bull sharks, like other sharks, learn patterns quickly. Many species of sharks have learned to associate specific sounds from fishing boat engines with food. When fish are hooked or trapped in nets, sharks may be able to obtain free feed. Dolphins do the same thing.
How can people stay safe?
Authorities have closed at least 20 beaches on Sydney’s northern beaches for 48 hours.
About the author
Vic Camilieri-Asch is a postdoctoral researcher at Queensland University of Technology.
Bonnie Holmes is a Senior Lecturer in Animal Ecology at the University of the Sunshine Coast.
This article is reproduced from dialogue Licensed under Creative Commons. read Original article.
This is a good move as it will give Darkness some time to clarify. But complete removal may take longer than that.
As shark experts, we recommend going one step further:
- Avoid swimming in murky water if possible
- Avoid swimming in Sydney Harbor after heavy rain
- Avoid surfing at inshore beaches until the dirty water clears
- Avoid swimming where people are fishing, especially where fish cleanups are taking place
- Avoid swimming in areas where bait fish are common, including where other marine predators such as dolphins hunt
- Monitor your local council and state fisheries websites for the latest information on keeping sharks smart this summer.
It is important not to exaggerate the risks. Nearly all negative interactions reported in the Australian Shark Incident Database come from test bites, or accidental bites from people fishing or even feeding the sharks.
For years, Queenslanders have had to adapt to the year-round presence of bull sharks in rivers and coastal waters. People don’t swim in bull shark hotspots like the Gold Coast canals or the Brisbane River. Authorities recommend avoiding swimming and surfing for several days after heavy rain.
As the ocean warms, bull sharks may spend more time in Sydney Harbor and other New South Wales estuaries. Sydneysiders and New South Wales residents may have to adapt to their long-term presence.