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Shark barrier is effective and green
Author: Prof Conrad Matthee
Published: 14/05/2013

​​​​​This is the twelfth in a series of articles about sustainability and specifically sustainability within the University. What are our staff members contributing in their fields of expertise; in which sustainable projects and initiatives are they involved and what contribution do they make to this important issue in the rest of South Africa? Are you busy with sustainability actions? Let us know at so we can inform the rest of the campus about it.​

Shark barrier is effective and green

A team of Stellenbosch University researchers has developed an eco-friendly and highly effective shark barrier, known as "Sharksafe". This is an alternative for shark nets which result in the death of thousands of sharks and other sea animals every year. Prof Conrad Matthee, head of the Department of Botany and Zoology, is actively involved in the development of the barrier and provides guidance to the research team. He tells more about what this entails…

What led to the research?

Due to the presence of shark nets in the sea shark populations are declining drastically. It is estimated that shark numbers have decreased by up to 90% over the past 20 years – particularly the number of great white sharks. Sharks are top predators and if they were to be taken out of the ecosystem, the latter will be disrupted. It is for instance speculated that there is a direct relation between the decline in shark numbers and the decline in other bony fish species.

Shark nets have been introduced with the specific purpose to kill sharks, but also result in the death of many other sea animals, such as dolphins and sea turtles. Great pressure is currently being put on countries that are using shark nets, to do away with these – among others Australia, USA, Japan, Argentina and South Africa.

In addition to destroying the sea life, shark nets are also not 100% safe for humans since they are not placed right down to the seabed and there are also overlapping gap areas where sharks can swim through. So, even though you are safer in an area with shark nets, you are not 100% safe.

What does the patent you have developed, entail?

We know that certain shark species, such as the Zambezi shark found in KwaZulu-Natal, are sensitive to strong permanent magnetic fields, while others, like the great white shark in the Cape waters, do not like kelp at all. We for instance saw how seals chased by sharks swam into kelp and how the sharks time and time again turned away, not entering the kelp areas.

Using these concepts we then developed a patent consisting of a rigid upright pipe which resembles kelp when it floats in the water. The structure also contains magnets to make it effective for various shark species. The pipes are anchored to the seabed and stand upright up to the height of the water level during high tide. Our structure has already been in the water for eight months and can resist waves of up to seven metres.

During our research we put bait behind the barrier to attract sharks, but no sharks swim through the barrier. In addition to the fact that the barrier looks like kelp to them, they are also being deterred by the magnetic fields. Since our barrier forms a "cage" consisting of loose pipes without a net, no sea animals are caught while sharks are kept out effectively.

We envisage that if the right material is used, the barriers will be able to remain in the water for at least 20 years with little maintenance required. We are already establishing that marine life grows on the cement blocks which anchor the barriers to the seabed, which now forms an artificial reef.

What is the next step in your research?

We intend to get permission to fence in the Muizenberg/Fish Hoek swimming beaches at an estimated cost of approximately R10 million each. The patent that we have in the water at present consists of three rows of overlapping pipes, but in the deployment phase we want to employ five rows of pipes. We would like to implement this with the developers of the so-called "mesh nets" which are currently being considered as alternative for shark nets – a finer woven net than the traditional shark nets. ​

We hope our green alternative will be supported by the City of Cape Town as it is environmentally friendly and also much safer for humans. It will be wonderful if the Cape beaches which currently enjoy blue flag status, all rather opt for the green alternative as a preferred choice.

We call our barrier "Sharksafe" because it keeps people safe from sharks while simultaneously protecting the sharks. For our team it is all about shark research and the protection of sharks. That is the driving force behind this research.

Are sharks really such a great danger to man?

Sharks are not interested in humans as prey. Great whites shorter than three metres (about four to five years old) feed primarily on fish. They then change their teeth and get those characteristically large teeth adapted for marine mammal prey. Their diet then changes seasonally from fish to marine mammals. Humans don't look like a marine mammal in the water, but the sharks are curious in nature leading to some negative encounters with humans from time to time. The problem of course is that one negative encounter can be fatal.

One of our team members, Mike Rutzen, regularly dives with the great whites. A shark tooth once hooked him to such an extent that he bled considerably. The sharks, however, were not interested in him. It is like walking into a pizza restaurant and smelling hamburgers – if you feel like a pizza, you will not buy a hamburger, particularly if you never smelled a hamburger before in your life and you don't associate it with food. The argument therefore is that all shark attacks are merely inquisitive in nature and that sharks are definitely not interested in hunting humans.

Who are the members of your research team?

Craig O'Connell is an American PhD student affiliated with the SU and is conducting part of his research on great whites in South Africa, and particularly on the effect magnetic fields have on sharks. 

Mike Rutzen is a private researcher and the main funder of the project and runs his own cage-diving company. He regularly dives among sharks in their natural habitat and is an expert in shark behaviour.

Sara Andreotti is a PhD student at the SU who is doing research on the genetics of sharks and takes identity photos of them. In her research she has identified more than 400 great whites in Gansbaai.

I am an evolutionary biologist with a genetic background in marine organisms and gives study guidance to some of the members of the research group.

Photographer: Michael Rutzen



Tobie KockTobie Kock2014-01-22T12:51:44ZAppears to be great! Now get it going and working so that the old system can be replaced before it is too late.
Amanda BarrattAmanda Barratt2013-09-09T06:20:41ZAn excellent idea, hope to see the tide turning and people latching onto the idea that the nets are a bad idea and culling sharks is not the answer!
ernie barnardernie barnard2014-07-16T17:18:03Zmythbusters a tv program in the state,says they have proved that a magnetic field dose not stop sharks that it is just a myth
AntonyAntony2014-03-22T12:31:59ZCool. I love the idea to incorporate kelp & magnets. Any thoughts to some type of diagnostic system that can detect a broken or compromised barrier? Like a cable w / single transmitter?
Daniel LehmannDaniel Lehmann2013-09-10T11:31:21ZBrilliant! I really hope the City of Cape Town adopts this system on the two beaches as a trial. It will have to be closely studied and can then hopefully be implemented further afield. If this comes down to a petition you can count on my signature! We need more lateral thinking to come up with more effective and mutualy beneficial innovations. Keep up the good work! Daniel Lehmann Intrepid Design, JHB