[imagesource: Ralph Watson / CICT]

Over the weekend,  the Marine Dynamics / Dyer Island Conservation Trust (DICT) was notified that there was a great white shark stranding at De Gruis, Gansbaai.

When a team, lead by DICT marine biologists, analysed the body of the 3,6-metre female shark, they found a large tear between the two pectoral fins with the liver and heart missing, which are the telltale signs of killer whale, or orca, predation.

You may recall the very rare footage filmed off the coast of Knysna earlier in the year, which showed a pair of orcas hunting a great white.

According to a blog post in SharkwatchSA, “two days prior there were confirmed sightings in False Bay, Cape Town of the orca pair, Port and Starboard, known to predate on various shark species, including white sharks”.

Yup, looks like Port and Starboard are still at it:

The carcass also showed signs of multiple shark bites along its pelvic area, likely a result of scavenging after the initial predation. There were no signs that fishing gear was responsible for the death and no tag was observed on the shark. The DICT team took multiple samples, including fin clippings, muscle, vertebrae, gills and jaws.

Some images of the shark carcass, taken from the same SharkwatchSA blog post:

You can see more images here.

Wilfred Chivell, CEO of Marine Dynamics, says that commercial overfishing and removal of prey species has had an impact on the disappearance of great whites in the Gansbaai area, but added that “the impact of orca predations on white sharks in Gansbaai is simply undeniable”.

Senior White shark biologist Alison Towner added the following:

“We have monitored the behaviour and abundance of white sharks in the area for over 13 years through an established long-term boat-based and tagging data program. The interactions between orcas and white sharks were first observed in 2017 and seem to occur at similar times each year, although we are only seeing the shark carcasses that wash out, they are all notably larger white sharks, above 3 meters in length.

This is concerning for a species that does not reach reproductive maturity until after this size. Collaboration between key experts, scientists, and stakeholders are paramount to proactively preserve the future diversity of Southern African shark populations and we thank the members of the public who have provided important information regarding these issues.”

Whilst Plett and the surrounding coastline seems to have a few resident great whites, the Cape’s dwindling numbers have been of great concern for a number of years.

Love them or fear them, great whites are an integral part of maintaining a balanced underwater ecosystem, as well as being responsible for a huge amount of ecotourism and job creation, and protecting the species should be seen as a priority.

[source:sharkwatchsa]