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
Wednesday, 27 May 2015 08:50

Great White Shark Pups

Very little is known about the location of mating and pupping of Great White Sharks. A Great White Shark birth (and mating) has yet to be photographed/filmed/or otherwise documented anywhere in the world!  They are ovoviviparous, give birth to 2-14 live pups, and may only produce 4-6 litters in a lifetime. The size of newborn pups can be up to 1.5m, and they are highly mobile from birth, further complicating our understanding of where they are born.

Due to the warmer waters brought on by this year’s El Niño, baby shark season has officially begun off the Southern California Coast. White sharks throughout the world move inshore during certain seasons. It is very rare to see adult Great Whites along the Californian coastline. However, the presence of large adult females and then the immediate presence of young pups (<1.5m) strongly suggests that these waters are also a white shark pupping ground from spring – early summer

In Southern California, white shark pups favour many of the same coastal fish species that humans do, like halibut.  So it should come as no surprise that white shark pups are often caught accidentally by coastal fishermen as bycatch.     

Dr Chris Lowe and his students took advantage of this great opportunity to work with local fishermen in the area in order to study baby white sharks.  From their catch/tag/release study, the Lowe Lab found that these white shark pups follow fairly predictable behaviours inshore, staying shallower than the “isotherm” at 60m depth.  Isotherms are boundaries in the water column between warm surface waters and cold deep waters. White shark pups don’t stray deeper than the 60m mark, whether they are in relatively shallow waters or in the deeper waters of the continental slope.  This shows that their choice in habitat relates to water temperature. 

Dr. Lowe and his team release a juvenile white shark back to its inshore waters.

Fewer large predators and an abundance of food, like stingrays and flatfish, draw sharks to the shallower waters

The great white shark is most commonly associated with the coasts of Australia, California and South Africa, but there have been occasions when this increasingly rare animal has been spotted in the Mediterranean. Some experts believe that the Mediterranean is a nursery where great white sharks give birth. The Sicilian channel, near the Italian island of Lampedusa, is the only location in the Atlantic region where both pregnant females and newly born great whites have been sighted. The warm waters of this particular area of the Mediterranean are high in nutrients and attract large pelagic fish, dolphins and turtles which form the staple diet of great whites. This area is a shallow shelf area which keeps the young in warm water throughout the year and reduces competition from blue and mako sharks.

Interesting facts obtained from Dr Lowe and his team:

While it’s rare for white sharks to become stranded on the shore, baby salmon sharks, a close cousin to the white shark, will often strand themselves because of a bacteria that infects their brain and causes them to die, according to Dr Lowe.

85% of all the great white sharks that are by-caught in their study area were <1.75m in length 

These sharks were often found alive when the soak time of the fishing nets was less than 20hr

When released, 92.9% of the pups survived - those are some tough babies!

Published in Latest News
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