Australian woman attacked by Shark.

A sixty-three-year old Australian woman is being treated in South East Regional Hospital in Bega, New South Wales, after being attacked by a Shark while swimming at Merimbula on Saturday 13 March 2021. Paramedics were called to the beach at about 6.45 am local time after witnesses described seeing the woman 'bumped' by a large Shark during an early morning swim. She was taken to the hospital with puncture wounds to the shoulder, back, hips and buttocks, although her injuries are not thought to be life-threatening. The species and size of the Shark have not been identified, and local authorities have closed a 30 km section of beach for 24 hours while attempts are made to determine if the Animal is still in the area using surveillance drones.

 

Beaches around the South Coast town of Merimbula are closed for 24 hours after a Shark attack. Kate Aubrey/ABC News.

Despite their fearsome reputation, attacks by Sharks are relatively rare and most attacks on Humans by Sharks are thought to be mistakes. Sharks have a diverse diet, including invertebrates, Fish, Birds, Marine Reptiles and Marine Mammals, which we superficially resemble when we enter the water. Marine Mammals are attacked principally for their thick adipose (fat) layers, which are a nutritious high-energy food, but which we lack. Due to this, when Sharks do attack Humans these attacks are often broken off without the victim being consumed. Such attacks frequently result in severe injuries, but are seldom immediately fatal, and victims are likely to survive if they receive immediate medical attention.

Despite this general rarity, Australia appears to be suffering a sharp rise in Shark attacks, with 51 recorded Shark attacks in Australian waters in 2020, eight of them fatal.

Marine biologist Julian Pepperell has suggested that this increase might be linked to a rise in the number of Humpback Whales, Megaptera novaeangliae, passing through Australian waters each year. Humpback Whales are a significant food source for many Sharks; adult Whales are beyond their hunting capacity, but do die of other causes and are enthusiastically scavenged, while larger Sharks such as Great Wights will attack Whale calves. Around 35 000 Humpback Whales currently migrate through Australian Waters each year, according to  zoologist Vanessa Pirotta of Macquarie University, a number which is growing by about 11% each year.

Humpback Whales were nearly exterminated by commercial Whaling in the first part of the twentieth century. The species has been protected since 1946, and in recent years their population has appeared to be recovering in many areas, now being seen as being of Least Concern  under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species. The Whales are recovering in many parts of the globe, and are starting to appear in areas where they have not previously been recorded.

 

A Humpback Whale, Megaptera novaeangliae, off the East Coast of Australia in July 2017. ABC.

An alternative hypothesis is that the rise in attacks could be linked to a La Niña weather system, which has brought cool water conditions to areas of the central Pacific where the Sharks are usually found, causing them to seek warmer waters closer to the Australian shore, where they encounter, and therefore bite, more Humans.

The La Niña weather system is the opposite of the El Niño weather system, in which unusually cold surface temperatures spread across the equatorial Pacific from the upwelling zone on the South American coast. This traps warm water from the western Pacific, preventing it from spreading east and warming the central Pacific. This leads to lower evaporation over the (cooler) east Pacific, leading to low rainfall on the west coast of South America, and higher evaporation over the (warmer) west Pacific, leading to higher rainfall over East and Southeast Asia and northern Australia.

 

The effects of a La Niña weather system in December-February. NOAA.

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