07 July, 2013

New white shark aggregation area in South Africa!

Dicken et al. 2013.  White sharks Carcharodon carcharias at Bird Island, Algoa Bay, South Africa.  African Journal of Marine Science.

Perhaps this area isn't 'new', but this is the first time white shark presence at Black Rocks/Bird Island has been quantified and published.  Unfortunately the paper is not open source, so you will have to ask your academic friends to download a PDF for you.  This area highlights yet another aggregation determined by the presence of seals even though it occurs in the warm Agulhas waters, and also shows small shark sizes when compared to our stomping grounds.  Yet, I am dubious of the accuracy of surface white shark sizing.  Anyone who has been on a cage diving vessel has experienced a good debate of 'hoe lank is dat haai', and the ranges can be startling!  Also, as boats/cages get larger, so do shark sizes.

A good example of this is Gansbaai local, Nemo.  When all the cage diving operators were working with ~3.0m long cages, Nemo was sized at around 3.0m.  Then, when cages suddenly upgraded to 4.0m in length, Nemo suddenly grew to 4.0m in length and the sizing debate began...  Here's hoping that someone who has/is/will be using those laser measurement systems on white sharks publishes a nice comparison between observer bias, surface sizing and laser sizing!

But I am digressing as usual.  Check out the paper!

No comments:

Post a Comment