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  • In Gansbaai, the largest white shark ever caught was at Danger Point and measured up to 5.9m. The exact world record white shark is a contested issue, but chances are it is between 6-7m.

  • If you see a white shark in the water don’t panic. Chances are high that the shark has already detected you and isn’t interested. White shark attacks are normally associated with poor visibility, so avoid murky conditions.

  • White sharks have a unique system called a “counter current heat exchange”, which keeps their body  tempreture +/- 7C above the surrounding water temperature. 

  • All sharks have an incredibly unique system on the tip of their nose called the “ampillae of Lorenzini”. These are small pores filled with a gel that transmits the electrical currents in the water to the shark’s brain so that it can assess its environment.

  • White sharks give birth to live young (not eggs), and they give birth to 6-8 pups at one time. Pups are usually between 1.0-1.5m in length and are born with teeth.

  • Body language has been a well documented form of shark communication and has identified body arching, jaw gaping, and other postures as specific social tactics.

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When does a white shark come up to breathe?

Tuesday, July 03, 2012 |  1 Comment Tags: Great Oxygenation event,

Author: Michelle Wcisel (Marine Biologist)
To Michelle, a born and bred American from Michigan, the sea resembles another planet within Earth where intelligent "extraterrestrial" beings and thriving systems flourish in the depths where there is neither oxygen nor sunlight. "So many of us gaze at the stars in wonder when we should be looking into our oceans!"

Have you ever wondered how sharks breathe?  Never fear, the Marine Dynamics shark fact blog is here!  Shark do not breathe oxygen from the air with lungs like we and dolphins do, so for this reason sharks do not surface to breathe. You would be shocked how many times this question rears its ugly head on Slashfin!  Now that that's out of the way, lets dive into the science...

First off, why do most animals breathe oxygen today?  The answer to this question is more incredible than you may realise.  In the history of life on Earth, the largest extinction of most life was the "Great Oxygenation Event" not the dinosaur comet.  2.5 billion years ago, a new life-form (cyanobacteria) was multiplying at an alarming rate and producing so much free oxygen  that it saturated the atmosphere and leached into the oceans. Before this period, most life on earth was anaerobic so this massive oxygenation killed the majority of living organisms on Earth. Oxygen, then, was an incredibly poisonous gas.  This extinction left a massive niche for organisms that could metabolize oxygen, and this lead to a new explosion of life forms that all us oxygen breathing beings can trace our lineage back to.  Does this history sound a bit familiar to the CO2 crisis we are seeing now?  Life will carry on, just we won't be a part of it...

Off my soap box and onto the sharks, most fish need oxygen to live but extract oxygen from the ocean using gills.  Most shark and ray species have 5 gill slits running on each side of the head, and as a shark moves through the water the water passes over these gills and specialized thin lined blood vessels within absorb oxygen.  Just like how specialized blood vessels within your lungs absorb the oxygen and transport it to your circulatory system.  That's the basics, but some of the physiology behind it is so awesome, so if you're game, keep reading. 

Unlike bony fish, sharks and rays do not have a protective covering over their gills (called an operculum).  This covering aids ventilation of gills, which is why most bony fish do not have to constantly move to keep water flowing.  You know how kids (and many celebrity women pout faces) make fish faces using their hands on either side?  Those hands are actually mimicing the water flushing action of the operculum.  Most sharks must move in order to breathe, which we discussed already in the "How do sharks sleep" blog.  But some bottom dwelling sharks also have spiricles which are small valves positioned behind the eye that move water over their gills even if they are stationary (pictured below). 

This is a great example of a physiological 'problem' with two branches of evolution coming up with two very difference solutions.  Due to their structures, fish must, one way or another, flush water over their gills.  The boney fish branch made an operculum and the slow bottom dwelling sharks made a spiricle



 

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