Alison Towner, white shark biologist for the Dyer Island Conservation Trust, enlightened guests at the recent Marine Dynamics marine evening with an overview of orca sightings in Gansbaai over recent years and the much publicised event of orca predation on three deceased white sharks retrieved and dissected.
Alison began by talking about the comparisons between great white sharks and orcas, detailing the statistics on predators, their size, and reputation that both have in the box office world (Jaws versus 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 orcas 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 orcas are nicknamed Port and Starboard as they both have drooped dorsal fins, one to the right and one to the left. Alison was present at each white shark retrieval, and arranged the onsite autopsies; the third one she led with the DICT team on the 7th May.
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.
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.
Thanks were extended to the Gansbaai community for the reporting of the deceased sharks to the Trust.
