June 20, 2017
Hello again, so far in the first few blogs I have spoken mainly about things that aren’t related to research such as the Shark dive which I mentioned in the last post. However, this is the blog post in which I will be talking about all the research that Marine Biologists and volunteers will work on in their time with the White Shark Diving Company.
Up until last year it was believed that there were between 800-1000 White Sharks left in South Africa. But last year Dr Sara Andreotti conducted a study into the potential population of White Sharks in SA. Sara and Mike Rutzen of Shark Diving Unlimited went to all the major areas of SA where Sharks are known to congregate and did mark-recapture surveys. Sara Andreotti found that in actual fact there are far less than previously estimated with a staggering number of only between 350-500.
Mark-recapture is very simple, you take a photo of a selected area of an animal and if in the future the same animal has its photo taken you can compare characteristics in both photos to try and determine if it’s the same animal or a different one. This method is used on many large charismatic marine species such as Whales, Dolphins, Whale sharks and White sharks.
The characteristic looked for on a White Shark is the Notches on the trailing edge of its Dorsal fin. Each notch pattern is specific to the individual, just like our fingerprint. In places such as Guadalupe they use mark-recapture surveys, and use the White patterning on the underside of the Shark in the Gill and Tail area, they are able to do this because the visibility of the water is usually a lot better making it easier to carry out these observations. Due to the low visibility in the water here in SA, looking at the notches of the dorsal fin is usually the best method of identifying the Sharks.
The method we use to collect these results relies on good team work, one person stands on the top deck of the boat and takes information on the shark’s behaviour; such as how many times it passes the cage and manages to get the bait. The person on the top deck also writes down any distinct markings such as scars and cuts that will help to identify the Shark during the boat trip. These markings are taken to help when Mary and Imke take fin photos, they will shout out the photo code from the camera, which is taken note of along with the distinct markings and when we are done we can match the markings to the photos and take note of the codes in order to help with analysis in the future.
Fin analysis may sound boring but it really isn’t! The fins are downloaded and the codes are read out from the sheet that was filled out on the boat. A fin picture is decided on its clarity, if the side of the fin is parallel, and if the whole fin plus the notches can be seen well. Then the fin is split into 3 sections; top, middle, bottom. Then the notches are circled and counted, as an example of counting; if there 3 in the top part of the fin, 8 in the middle and 6 in the bottom then the code for the fin will be C_030806. This code is then checked in the database to see if it’s the same shark. If that code doesn’t exist then other codes close to this number will be checked to see if more notches have appeared or if notches have disappeared. If a shark is matched then the new fin picture is placed into the already existing database and a re-sight date is placed in the form. If it’s a new shark then the new shark will be placed into its own folder and a first sighted date will be placed into its profile.
So far, the WSDC have around 100+ shark profiles and that number goes up every time they do fin analysis, it’s amazing to be there when they identify a new shark and even better when they match up an already existing shark.
The reason why this study is so important is because the White Shark is a protected species under the IUCN and has been a protected species for a long time, but if you go to South East Asia you can still find their fins and other products such as their teeth or jaws on the market. Which means people out there are still illegally fishing and killing these beautiful animals. WSDC is working alongside Sara to try and get another population estimate hopefully in the next two years so we can see if the population has increased or decreased, then we can work to strengthen laws on their protection.
You may have heard about shark nets up the East coast of Africa, these nets are in place to protect swimmers at the beach. In fact, these nets are useless as the nets don’t even go to the bottom so the nets don’t actually stop sharks from swimming into the shallow water, most of the sharks caught in the nets are actually on the beach side of net meaning that as the sharks make their way out they get caught. These nets don’t just catch sharks either, they catch everything from sharks, turtles, whales, seals, birds and many more. If you can name it these nets catch it. In the period between 1978 – 2008 these nets caught 1000 White sharks, which if you think now SA only has 350-500 that is a large chunk of the population which was killed pointlessly.
The shark safe barrier research is eco-friendly and non-lethal to sharks and other wildlife. It has hollow tubes with magnets inside which are specifically designed to deter large predatory sharks such White sharks, Tiger sharks (Galeocerdo cuvier) and Bull sharks (Carcharias leucas). It has also been shown that large predatory sharks don’t particularly like kelp beds as they can become tangled and injured, so the shark safe barrier is designed to look like an artificial kelp bed. This, alongside the magnets deter the sharks away from it and so far testing has had a 100% success rate. With no sharks crossing the barrier even when chum, bait and everything that a shark would be attracted to is on the other side.
This is a perfect tool to be used to protect both swimmers and sharks alike from injury and is hopefully a method that will be implemented not just in SA but throughout the rest of the world.
An infographic is located below just to give you some further information on both the shark safe barrier and the Dorsal fin ID project.
White sharks may be the only large predatory shark in the bay but there are many smaller shark species that live around the area and can be found in very shallow water, and in or around the Kelp beds and reefs that are found here. The problem with these smaller species is that because they can be found in many areas, they are exploited by commercial fishing in the area.
These smaller shark species are a staple part of a juvenile White Shark’s diet, as they grow older their diet changes to included other larger mammals. However if the smaller shark species populations decrease then this will result in a decrease of food for young white sharks, resulting in an even lower White Shark population in South Africa.
This study focuses on catching, measuring and tagging the sharks before releasing them. The species of sharks caught have almost no data on them whatsoever so this study is incredibly important on shedding light into a lesser known group of sharks. When the sharks are caught they are measured and tagged with a plastic non-harmful spaghetti tag. This tag has a code and contact number to ring if it is caught. If it is re-caught by a member of the team then it is measured and the new data is placed against the already existing data to get an idea of its growth rate and movement patterns.
Genetic samples (Fin clip) are also taken from each shark for genetic studies being carried out at the University of Stellenbosch. A small section of their fin is cut away and placed into a vile with alcohol to preserve the sample. This then gets sent off along with the Tag data to the researchers in Stellenbosch to aid in their studies.
This isn’t to do with research but it’s an amazing program that’s being run by the WSDC, every Monday, Mary will go to the local school “Gansbaai Academia” where it has a marine club. This is where Mary will go and teach the local children about the marine life they have living literally on their doorstep. Some of these children have never been in the ocean before and it was amazing to be there whilst these children went into the ocean for the first time.
The children get taught everything from Bacteria and Plankton all the way up to Sharks and Whales. The amazing thing about this program is that it’s educating future generations for the need of conservation, care and awareness in order to protect the jewel of an ecosystem they have sat in their backyard.
I know this a lengthy blog post but then again there’s so much that is going on down here and so much good that is being done that they deserve the credit of their research being brought to your attention and I hope that you have also walked away learning something new about the local ecosystem down here in sunny South Africa.
Until next time guys, and thank you for reading.