Great White Shark vs Orca May 2017

June 08, 2017 Brenda du Toit

May 2017 was an interesting yet trying time for the team of Marine Dynamics and the Dyer Island Conservation Trust who were called out to retrieve three deceased white sharks in a space of a few days – a female of 4,9m and two males at 3,6 and 4,5m. All three sharks have been identified from our extensive database.

Our shark biologists, Alison Towner and Kelly Baker assisted by our team and experts in their field including Dr Malcolm Smale, and with the permission of the Department of Environmental Affairs did the dissections on site in Gansbaai. All three sharks had consistent bite wounds and were found to be missing their livers. This indicates what is known of orca predation on sharks as they attack and stun the shark into tonic immobility and the buoyant liver rises to the surface through the injury. The squalene rich liver is the only part that the orca’s appear interested in although the one male shark was also missing a heart. This is the first time ever that a white shark has been dissected after an orca predation and this is the first official observation in South Africa stunning researchers and shark lovers.

In the last two years we have had more frequent sightings of Orca’s and there has always been speculation as to how the orca’s affect shark behaviour and now we have confirmation that some orca’s do indeed pose a serious threat to our already vulnerable population of Great White sharks on the South African coastline. The orca (Orcinus orca), also known as the killer whale, belongs to the dolphin family and is the only know natural predator of the very legendary apex predator, the Great White shark.

Alison Towner, white shark biologist for the Dyer Island Conservation Trust, enlightened guests at the Marine Dynamics/DICT marine evening with an overview of the two predators.  Alison began by talking about the comparisons between Great White sharks and orcas, detailing the statistics on both predators, their size and reputation that both have in the box office world (Jaws vs Free Willy).  “Orca sightings in Gansbaai were rare up until the last five years where different pods have been spotted more frequently closer to shore”, said Alison.  Dyer Island Cruises team recorded boat based observations of marine mammals for over a decade and ones that the team are aware of include two orca’s off Danger point in 2011 and then a pod of 5 in 2012 that were filmed chasing common dolphin from behind Dyer Island. There was an elusive pair of orcas first sighted in 2015 behind Dyer Island and again in 2016, then right before the three deceased white sharks washed up in Gansbaai and Struisbaai in early May 2017. The two orca are nicknamed Port and Starboard as they both have drooped dorsal fins, one to the right and one to the left.

WATCH two orca’s off Danger point here

Alison explained what is done at these autopsies using a series of photographs detailing scientific measurements, samples, body parts and injuries to each deceased white shark – all used for varous scientific studies. The orca predations were put in a broader context explaining where else it has happened, namely California and Australia and why this South African situation was so novel as it was the first time white shark carcasses were available for examination after orca predation. The reality is both orca and white shark are highly transitory ocean predators, and even though there is a definite impact with sharks seemingly fleeing the Gansbaai area temporarily as a result this is all part of the natural ecological balance.

The full timeline of the retrievals and dissections can be viewed here

The cost of retrieving shark carcasses that weigh close to a tonne and can be in remote locations, autopsy equipment such as knives, scientific vials, ethanol etc can add up.

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