Thursday, 02 June 2016 11:22

White Shark Sightings

Winter in the Southern Hemisphere is known as the best season to view Great White Sharks. Here in Gansbaai, we have sharks all-year-round, but Winter is still traditionally considered as the best season. There are a few contributing factors, such as the fact that there are more sharks hanging around Shark Alley during Winter, the water visibility improves and the water temperature is a few degrees warmer than in Summer. Thanks to the Great White Shark’s rete mirabile, they are able to raise their body temperature about 10’C warmer than that of the surrounding water, which in layman’s terms relates to the sharks being a little lazy when the water is cold and when the water is warmer, they feel a little friskier. The big males make their appearance in winter, just in time for the Cape Fur Seal pups to take their first plunge into the Atlantic and test their aquatic skills. Generally, we see more females than males during Summer and more adult males during Winter.

If you look at our data from 2015 however, you will notice a pattern that does not support what I’ve just told you. Now, I understand that when it comes to the collection of Biological data, it is not as clean and neat as pure statisticians would like it to be; the variables are all over the place! I am all for statistics, it is fascinating, it gives us insight and better understanding, but sometimes it also gives us more questions than answers. And 2015’s data is very intriguing indeed...

Month

Male

Female

Unknown

NBR shark

January

43 52 33 128

February

125 124 80 329

March

79 142 64 285

April

48 142 39 229

May

22 91 27 140

June

47 98 29 174

July

71 78 26 175

August

58 81 48 187

September

22 37 25 84

October

49 100 41 190

November

23 63 33 119

December

42 62 50 154

The Western Cape of South Africa did not get its nickname “The Cape of Storms” for no reason; Winter in the Western Cape is infamous for its gale force winds and feisty cold fronts, which whips the Atlantic Ocean up into a frenzy and of course, has a direct impact on the amount of days we can go out to sea. Therefore, one could deduce a direct correlation between the amount of trips done per month and the number of sharks spotted. Which is probably why we saw nearly 330 Great Whites in February and only a 140 in May. We did not have good weather in January, so we had quite a few “no sea days”, but January is not known as a good shark-month, so one could expect a low number of sightings. September is still considered good shark-viewing season, but the weather did not permit many trips out to sea, which then gives us the self-explanatory low figure of 84 Great White Shark sightings.

 

But this is where it gets intriguing: why did we see so many males in February, if traditionally we see more females than males in Summer? And why do we generally see more adult females than adult males? The males we do see tend to be juveniles, which brings me to another question: why do we see so many juvenile sharks in our area? Could one be blamed, if one came to the conclusion that there may well be a Great White Shark nursery in our waters? I mean think about it: Lots of adult females, not so many adult males, and loads of little juveniles of about 1.2m in length, which is practically newborn size. Hmmm, it does make you wonder, doesn’t it?

Now if you consider the strange phenomena we experienced during January and February of 2016, where we had no shark sightings for 5 weeks; could these hiccups in our 2015 pattern have been the warning signs of the impending crisis, much like cumulus clouds are the forerunners of a storm? Were these hiccups caused by the El Nino and can we indeed blame the El Nino for making our sharks disappear for those weeks? Guess we will have to wait until all the data has been accumulated and assessed – will keep you posted!

 

Published in Latest News
Tuesday, 19 April 2016 07:55

8 Facts about the vision of Sharks

1. Effective up to 25 meters

2. 10 times greater than humans in clear water

3. Eyes very similar to humans – cornea , lens, retina, iris, pupil

4. Contains rods and cones so can detect colour and see in low light – new research (2011) shows not all sharks have the same cones cells, bull sharks cannot see in colour.

5. Tapetum lucidum – detects very small amounts of light which is why they can see in very murky water

6. Can see out of the water as well – pupil dilation

7. Iris is a vivid blue colour

8. Nictitating membrane (eye lid) lacking in great whites so they roll their eye back for protection

Published in Latest News
Thursday, 19 February 2015 07:41

Remains of a 15-million-year-old shark found

And in other shark related news;

Donald Gibson found the first vertebra just as he had begun to dig out the space for the sunroom he had promised to build in the back yard of his parents' home in Calvert County, Maryland, USA.Over the following week more and more vertebrae were found — each one about 18 inches deep into the groundBut then they found a straight column of vertebrae, two feet long as well as a tooth.

The digging stopped.

What the Gibsons unearthed were the remains of a 15-million-year-old Snaggletooth shark found, which palaeontologists say is more complete than any other fossil of its kind in the world.

The Gibsons' discovery is so unusual because of the number of bones they found — more than 80 vertebrae and hundreds of teeth, all from the same shark — as well as the position they were in and their unusually good preservation.

Palaeontologists Godfrey and Nance were called to the scene and they were amazed at the find. They immediately wrapped the entire skull cavity in a stiff plaster cast, like one used to set a broken bone.

Sharks' skulls are made mostly of cartilage, not bone, so they almost never withstand the ravages of time. Yet somehow, the shark that came to rest in the Gibsons' backyard sank belly-up when it died during the Miocene Epoch. It became buried in sand, then by sediment eroding from the Appalachian Mountains. And its skull cavity — containing hundreds of the distinctively shaped teeth, up to an inch-and-a-half long, that give the snaggletooth its name — kept its shape.

Using a microscope, the scientists digging in the Gibsons' yard were able to see the distinctive hexagonal shape of shark cartilage, fossilized and preserved.

Godfrey said that this shark was 8 to 10 feet long during its life.

Having preserved the teeth and surrounding remnants of cartilage in exactly the positions they were found in, the palaeontologists will be able to take CT scans of the cast and analyze the specific three-dimensional layout of the prehistoric shark's mouth, something scientists have never done.

"For the first time, we're going to be able to know what the dentition — what the teeth — looked like in this kind of shark," Godfrey said.Then they will remove the cast, gently clean each piece and put the discovery on exhibit.

Godfrey said he is receiving emails from palaeontologists up and down the East Coast who are excited about the discovery.The skeleton will allow scientists to compare the prehistoric snaggletooth, an extinct species, and modern snaggletooths, a descendant species that lives in the Pacific.

Comparing the teeth of snaggletooths then and now will help scientists understand the workings of shark evolution, the likely diet of prehistoric species and the climate during the Miocene Epoch.

And the fact that the spine and the skull cavity of the shark found by the Gibsons are definitively associated with each other, the most complete snaggletooth skeleton ever found will allow scientists to identify whether smaller pieces of future fossils come from snaggletooths or other species.

"When in the future we find just a single vertebra, we'll be able to say, 'This comes from that kind of shark.' And only because we have this association being made," Godfrey said. "It's just incredibly unlikely that we would make this kind of discovery."

Published in Latest News
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