Tagging success!

August 06, 2015 by dyertrust

Alison Towner
DICT Marine Biologist

It is now peak winter season here in the Western Cape. At this time of year we tend to get extreme cold fronts interspersed by one or two windless days followed by another cold front! On the morning of Tuesday 28th July, a 3m swell with very little wind provided us with a morning gap, so we grabbed the opportunity to launch our research boat Lwazi in an attempt to deploy our first round of R-code transmitters! To our joy we were able to successfully deploy tags on two individual sharks whilst we were anchored on a reef system west of Dyer Island called the Geldsteen.

The first shark to arrive was a 3.2m Female, who approached Lwazi very slowly making some really relaxed passes. Using a tagging pole we deployed the tag next to her dorsal fin, then she continued to circle us! Several white sharks paid us a visit that morning, the majority of which were sub adult males, under 3.5m TL. Next to arrive was a 4.1m male, also very relaxed. He made the perfect candidate for the deployment of our second tag, and just like the first shark, he came back to circle us with his tag in place! Subsequently, both sharks were seen days later at a couple of the cage diving boats. The boats have been excellent at letting us know if they see our tagged sharks. White Shark Projects were able to provide us some nice underwater images of our male shark.

We would like to extend a sincere thanks to the donors of each tag, Kelci + Thomao Reca and Kasim Kutay, clients of We look forward to deploying the rest of our tags over the next coming months and collecting their data on our listening stations for as long as possible. For more info on this project, including information on how to donate to our tagging please see our Contact Us:
Facebook: Jacques Costeau once said the best way to observe a fish, is to become a fish and this is exactly how one feels while descending on this dive! As we dropped down beneath the water surface our line of sight was immediately consumed by the vast shoals of Yellowtail comrading together like foot soldiers rushing to battle. Cow nose sting rays elegantly swept in and out between them. Impressive Kobaljeu and Spotted Grunter moved stealthily so as not to get in the way, whilst cartoon like Musselcracker or Poenskop hovered in their own little worlds. Every fish had its rank and knew its place. As we looked carefully on the floor, tiny nudibranchs hid themselves perfectly camouflaged amongst boulders. It truly was an enlivening experience. Glancing out the window at the childrens faces was equally as magical, to see their sheer bewilderment- from the perspective of the creatures swimming in front of them. It was a surreal juxtaposition to be the human intertwined in the world of a captive fish which we found very entertaining! Nicole beamed from ear to ear whilst waving excitedly at us through the window. We waved back, and noted her expression change as the silhouettes of two large Ragged tooth sharks approached us.

The Ragged tooth shark (Carcharias taurus) is quite different to the Great White. I like to describe them as the Jimmy Nail of the shark world (Jimmy Nail was the guy who sang the 90s hit crocodile shoes. My mum used to say hes so ugly hes attractive!). Raggies have an undue menacing appearance with their small beady eyes and snaggle like teeth. Pre 1990s fishermen targeted the species as they were perceived maneaters throughout much of their distribution.

 

 

This was before research confirmed they are very placid and actually extremely vulnerable to exploitation due to their slow reproduction. The two oceans aquarium have supported some of South Africas most critical ragged tooth research including the tagging and releasing of various sharks. Maxine was a large female ragged tooth caught in the KZN shark nets in 2004. She was rehabilitated in the aquarium and migrated far east when released with satellite tags. The species makes incredible large scale migrations from the Western cape to the East coast annually in SA. Maxine became a real ambassador highlighting these movement patterns during the popular public campaign.

Our dive lasted around 45 minutes, then Ilze and I surfaced with huge smiles very contented! Angie even gave Ilze a Raggies tooth which she said was especially for little Nicole. It was quite the luxury dive experience with a clean towel and warm shower waiting for us after- we did not even have to de-kit our SCUBA gear- Angie and the team had it all covered!

The great thing about the dive in the I&J predator tank is its warm, its crystal clear and theres an absolute 100% guarantee of seeing the sharks and other predators up close and personal! The staff go out of their way to ensure your comfort and safety. I would definitely recommend this as a must do dive in the Western Cape, especially if the Cape of storms is living up to her reputation!

A brand new predator tank is in the process of being built at the Two Oceans, which Im told will undoubtedly impress. As tourism and conservation partners the Two Oceans aquarium, Marine Dynamics and Dyer Island Cruises go back over a decade. It is a simple relationship; each business is geared around the same passion and drive for marine education and conservation. In fact, one of MD and DICS resident skippers Pieter du Toit was a shore angler who helped catch and tag ragged tooth sharks in Struisbaai during Maxines campaign in 2004!

Two weeks ago the Two Oceans donated 100,000 ZAR towards the building of our African Penguin and Seabird Sanctuary (APSS) which was an integral building block towards the development of the facility in Gansbaai. For more information on this see

Previous surveys have employed underwater visual census and capture survey techniques. The detection power, environmental impact and financial sustainability of these methods have limited their implementation, especially in the cold Benguela upwelling–? driven ecosystems on South Africas west coast. The baited remote underwater video system (BRUVs) has been tested as a standard, non–?extractive methodology that can be applied throughout South Africas near–?shore marine habitat areas.

BRUV surveys have been performed in both protected and exploited areas in South Africa, including False Bay, Bettys Bay, Stilbaai and Tsitsikamma. The standard BRUVs provide data on habitat, species diversity and abundance. The stereo–?BRUVs variation can give estimates of fish length. While fish length is a useful metric because it can be converted to fish size structure data, the stereo–?BRUVs require more complicated equipment for the deployment and additional software and time for the analysis of the length data. Therefore, the single camera BRUVs are more practical as a standard survey tool across South Africa.

The BRUV system operates by lowering a camera rig to the sea floor and recording approximately one hour of footage for later analysis of the habitat, number and behavior of the species within view. Deployments can be made simultaneously in groups of up to four rigs. Cameras are deployed at least 150 m apart to maintain sample independence.

This will be the first study of its nature around Dyer Island.

Staff from both the Dyer Island Conservation Trust as well as CapeNature will be trained to utilize BRUV systems during this studyand in the long term this will become a monitoring project for the Dyer Island Conservation Trust and the International Marine Volunteers in the Greater Dyer Island Region.

We thank one and all who attended this evening, it was by far one the most interactive audiences at our Marine evenings.

All visitors was also reminded that the African Penguin and Seabird Sanctuary is nearing completion, and that anyone is welcome to stop by to see the progress on sitethere will not always be people on had to show them around, but with the sponsorship of the horticultural layout by the Grootbos Foundation, it is worthwhile to stop and see the wonderful progress of the facility.

For any queries you are welcome to contact the DICT at
Inside the shark.

The first organ exposed when cutting into any shark, is the enormous liver. Aside from being the main detoxification unit, the liver is both a buoyancy aid as well as an energy reserve. White sharks break down nutrients from their food and store them in their liver as a form of oil called squalene. This female white sharks liver weighed 59kgs and was almost liquefied- it was by far the most grueling component to remove and weigh! The Necropsy was completed in five hours from start to finish. All the organs, measurements and necessary samples were collected, including the stomach which had the remnants of seal carcasses inside of it. The impressive jaw was cleaned down to the cartilage, then all of the samples were sent to government. The Dyer Island Conservation Trust is applying for a permit to display the jaw on site for educational purposes.

It is particularly sad when marine predators wash ashore deceased but we have to be mindful of the fact that it really does give us a unique opportunity to collect samples which would otherwise be difficult to obtain. The information collected from this female white shark will go towards several crucial studies improving our knowledge in areas such as genetics, diet, age/growth- just to mention a few. Simone Rizutto was able to take muscle samples for his eco toxicology work to assess levels of contaminants which have accumulated in the sharks muscles, and the stomach contents will go to Dr Malcolm Smale of Bayworld Museum to be used as part of a long term diet project.

White shark carcasses rarely wash ashore, it is more likely that they sink. The last white shark to wash ashore locally in Gansbaai was three years ago, in June 2012. It was a 3.8m (TL) male found on Dyer Island. The DICT successfully retrieved this specimen too, it was taken through to government for dissection, which revealed no obvious cause of death despite 6 cape fur seals in its stomach! (
All in all, the dissection was a huge success. The process would not have been possible without the large amount of effort combined with the quick execution of appropriate equipment by the DICT- as well as the dedicated hard work of all involved. We would like to make a special thanks to Pikkie Smal. This was the second occasion within the last two months Pikkie has phoned in to notifiy the DICT of marine specimens, the previous occasion had been a When the next day dawned, we donned our oldest clothes and gloves and got down to measuring, dissecting and collecting samples. Our International Marine Volunteers were given an impromptu lesson on dolphin anatomy, both inside and outso now they know how to tell the sex of a dolphin and they understand more about the differences between sharks and cetaceans.

This specimen turned out to be a male common dolphin, 2.3m long. The rostrum (beak) and lower jaw were broken, but it wasnt possible to say whether this occurred pre- or post-mortem. When we cut into the carcass and examined the lungs, they were spongy and full of airthis is a sure sign that the animal suffocated under the surface. Dolphins are conscious breathers which mean that they have to think about when to breathe (unlike humans). This animal would have thus held its breath because it was trapped underwater and could not surface to breathe. It is not unusual for this to occur because common dolphins are known to form part of the bycatch of our purse seine fishery.

Common dolphins are fast swimming animals and occur in large schools, following pelagic fish species (anchovy and sardines) up and down our coast. These are the dolphins that do all the hard work during the sardine run, rounding the fish up into dense bait balls in order for the whole school to feed, but then along come seals and sharks to help themselves as well, and even Brydes whales toothey can engulf the whole bait ball in one big mouthfuland then the dolphins have to start all over again!

Common dolphins are also crazy about bow-riding vessels and can swim up to 20-30 km/h! If you listen closely then you will hear them whistling while they porpoise alongside the vessel. They have a beautiful hourglass marking on their flanks, the front half of which is yellowish and the rest is pale grey colour.

We collected and froze several samples for further studies: a skin sample for genetics, a cross section of the testis for reproductive analysis, the stomach for diet analysis and the skull for the Mammal Research Institute of the University of Pretoria. They will process the samples and place the material in the Marine Mammal Collection at the South African Natural History Museum in Cape Town.

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