MOSSEL BAY NEWS - A rare opportunity to learn more about one of the apex predators in our oceans presented itself during May this year when a great white shark (Carcharodon carcharias) was found beached at Dias Beach, Mossel Bay. 

Three weeks prior to this event, three dead white sharks were found on beaches near Gansbaai that fell victim to orcas, the only natural enemy of white sharks and it was expected that the Mossel Bay shark might have met the similar fate.

However, there was no indication of any physical injury to this 3.2 metre female shark.

It was decided to do a public necropsy (a surgical examination of a deceased animal to identify the cause of death). The reason for doing this in public was to offer the scientific community and interested parties the rare opportunity to witness a necropsy and also show how important scientific data is collected and to educate a wider audience about the lives of these ocean dwellers as many people have never seen a white shark.

The necropsy was done by Dr Enrico Gennari (director of research – Oceans Research, Mossel Bay), Dr Malcolm Smale (Bayworld in Port Elizabeth), Alison Towner (marine biologist at Dyer Island Conservation Trust) and field specialists of Oceans Research, at the Dias Museum. Volunteers from S.M.A.R.T. (Stranded Marine Animal Response Team), staff of the Dias Museum and various other organisations attended the necropsy.

There was also the hope that fishermen would attend and leave with a greater understanding and new approach to their fishing practices.

The cause of death
The results showed the shark showed no signs of hemorrhaging and was in pristine health. She was absolutely capable of killing her favorite prey, a Cape fur seal, found in her stomach, with one bite. If she was in poor health, this would not have been possible as she would lack the strength and agility.

Except for the remains of a complete fur seal, some whale blubber from an (unidentified species) and the presence of steel trace fishing gear, no plastic was found in the stomach.

A blood sample that was taken showed extremely high levels of cortisol, catabolite, and lactate - all of which are released during extremely stressful events. The high levels indicate she had put up a fight of anywhere between five and eight hours. A large J-hook was found in her gut and it was determined that she died because of being hooked and struggled for many hours and it was determined that exhaustion and stress caused by illegal fishing, were the cause of death.

How to avoid catching White Sharks
Although it might not have been the intention of catching a white shark, fishermen should take care in areas such as Mossel Bay, where a large white shark population is found, to adhere to regulation and be prepared if one of these magnificent predators are hooked. Precautions may include the following:

• Do not fish in highly populated white shark areas

• If caught, lines/trace wire should be cut as close as possible to the animal

• Use lighter trace wire

• Have appropriate tools to dislodge or cut a trace

• Get the animal back into the water as soon as possible

It is, however, illegal to catch white sharks in South Africa.

White Sharks and their human enemies
The use of J-hooks can cause massive damage to critical organs of all fish species and leave them critically wounded. Commercial long-liners fishing close to shore and especially near white shark populations are a huge threat to the species which are considered as Vulnerable on the IUCN red list and are a CITES appendix II-listed species. Bather safety nets and drumlines deployed off certain coastines remain a constant threat.

Pollutants and chemicals within the ocean, and the ever-present and growing amount of plastic waste, also endanger the future of not only white sharks but also many other marine animals.

Environmental changes such as abnormal ocean temperatures and lowered oxygen levels due to global warming, alteration, and destruction of essential habitats and increased boat traffic (propeller damage) are also an issue.

Dr Enrico Gennari explained to all present what Alison Towers and Dr Malcolm Smale were doing  while Oceans Research field specialist Sasha Dines wrote down all the measurements.

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