Great White Sharks (GWS), the largest known predatory fish, have grown and adapted to the marine environment to ensure that they stay at the top of the food chain. Using 3 different adaptations (ambush predation, camouflage and specialised senses) to find and catch their food, they have mastered the art of hunting in the deep depths of the ocean.
Adaptation #1 – Ambush Predator
Ambush predation is the primary way that GWS hunt and catch their prey. Great White Sharks is a typical ambush predator and often hunts by taking its prey by surprise from below. Cruising along the bottom of the ocean, they can use their triangular vision to scan the oceans’ surface for potential food items. When they spot something juicy, they will swim upwards at speeds of up to 50km/hr and attack, dislocating their jaw to stretch it as wide as possible, catching their prey by surprise.
Breaching events occur often when the shark propels itself out of the water, and belly flops back into the ocean, prey in mouth, teeth crunched down. Without chewing, or manners for that matter, the GWS will chop up its food into smaller bits (using its 7 rows of razor sharp teeth and 1.8 tons of biting force) and swallow whole pieces.
Adaptation # 2 – Countershading
A further adaptation for hunting is what we call ‘countershading’. Countershading is the particular colouring of the GWS body where the top of their body (dorsal side) is dark grey and the bottom (belly side) is white. If you can imagine swimming above a GWS and looking down on the shark – their dark dorsal side will blend in with the dark depths of the ocean, and if swimming below the GWS and looking upwards at it, the white belly of the shark will blend in with the bright white light of the sun glare above. This countershading enables the GWS to blend effortlessley into the ocean, and hence, ambush their prey.
Adaptation #3 – Senses
Using their many specialised senses, the GWS can feel the movements of potential prey items in the water – and therefore find them even when water visibility is poor. More specifically, using the Lateral Line (which runs along the sides of their body), they can detect vibrations and changes in pressure caused by currents and other animals. Another sense, the Ampullae of Lorenzini, (a set of electro-magnetic receptors) can sense electric and magnetic fields in the water – which are emitted by living organisms usually from their heart beat.
With these senses activated, our music/sound attractants come into play!
Why are the GWS at Neptune Islands?
The Neptune Islands Conservation & Marine Park is home to Australia’s largest colony of Long Nosed Fur Seals with half of the entire Australian population breeding here. The fur seals enjoy the year-long variability and abundance in biodiversity available in the area, influenced by the warm Leeuwin Current in winter and the cold Flinders Current in the summer.
Researchers assume that the GWS are aggregating at the Neptune Islands to feed on these many thousands of seals that live here. However, predation events are rarely observed. It may be that the sharks are exercising a different hunting behaviour in this location, as compared to other aggregation sites around the world where breaching and ambush predation is common.
However, without continued observation and research here at the Neptune Islands, we will not be able to look into this behaviour further – giving importance to the continued presence of the Shark Cage Diving industry, our customers’ first-hand observations and those of the crew.
Where else are they?
To be honest, it is impossible for us to know where every GWS across the entire globe is all the time. However, research has given us some information of where they can be found most of the time. They are usually found in cold, temperate and tropical waters, in an area between latitudes 60 degrees North to 60 degrees South (see image above).
GWS can travel distances of 75-100km per day. As well as location migration, GWS have vertical migration (movement up and down in the water column) – usually spending the daytime periods on the bottom of the ocean and night time on the surface. They have also been found to spend more time on the bottom of the ocean in the gulfs of South Australia, and more time on the surface in migrations to Western Australia.
With such large migrations and the fact that they don’t hang out in large groups – these sharks are extremely elusive and hard to study. There is still so much to learn about these amazing animals and their hunting behaviours. We hope that with our continued visits to the Neptune Islands, and our extensive data collection projects, we can continue to investigate the lives of the GWS and capture any ambush predation events in the future!