Man dies after Shark attack in Western Australia.

A 55-year-old man has died after being attacked while body-boarding off Cable Beach on the north coast of Western Australia on Sunday 22 November 2020. The incident happened at about 8.40 am local time, with the victim being pulled from the water and given first aid immediately, but dying at the scene. The Shark remained in the area for about an hour after the incident, with witnesses identifying it as a Tiger Shark, Galeocerdo cuvier.

 

The approximate location of the 22 November 2020 Shark attack. Google Maps.

Despite their fearsome reputation, attacks by Sharks are relatively rare and most attacks on Humans by Sharks are thought to be mistakes. Tiger 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.

 

A Tiger Shark, Galeocerdo cuvier. Albert Kok/Wikimedia Commons.

Despite this general rarity, Australia appears to be suffering a sharp rise in Shark attacks, with 22 recorded Shark attacks in Australian waters so far this year, 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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