Tuesday, June 10, 2014

Great White Shark eaten by even bigger Great White Shark?

 The story that a tagged great white shark has been eaten by another great white shark is making headlines around the world. Various news outlets like UPI are reporting that "Australian scientists are searching for a "mystery sea monster" that likely devoured a nine-foot-long great white shark they'd been tracking." and People magazine is saying  it was a "colossal cannibal great white shark"  and even stating that it's size is "estimated at 16 feet long and over 2 tons"

Now what has lead these "scientists" to this conclusion? In the following video they say that the shark suddenly plunged to 580 meters, about 1900 ft., where the temperature of the tag went from 46 degrees farenheit to 78. (BTW. the tagged shark shown at 2:12 in the video, is actually one of our Guadalupe sharks) People magazine states that "They (the researchers) end up coming to the terrifying hypothesis that a "colossal cannibal great white shark" – estimated at 16 feet long and over 2 tons – snacked on his lil' buddy. The scientists offer several suggestions as to how this nightmare become reality: Perhaps this was a territorial dispute, or maybe the larger shark was so hungry it was driven to attack another of its own species" 

Wow, that is amazing! They not only know that this shark has been killed, they also know what killed it and even estimate the size of the killer. How the heck did they do that? Estimate the size and species of a predator by the temperature of a tag. And here I was, finding it incredible that another guy claims to be able to do that by the shape of a dorsal fin.

So let's look at a few facts. The great white sharks do indeed maintain a body temperature of a few degrees above the water temperature. According to Elasmo-research.org, great white sharks maintain a muscle temperature of 7-9 degrees f, and a stomach temperature of 13-25 degrees f above water temperature. The scientists claim that the tag could not have fallen off, because it would have recorded a lower temperature first, before the jump to the higher temperature, after it was eaten. So if that were true, that would put the maximum temperature inside a great white shark stomach at 64 degrees and not 78. 

Since the tags we are talking about here, are external, they record the temperature of the water and not that of the sharks muscle. Therefore, they would not have recorded a lower temperature after falling off. The fact that it plummeted straight down to 1900 feet is a further indication that the tag fell off. If another shark had attacked this 9+ ft great white, there would have been a struggle and they would not just have plummeted down. Also, the typical attack behavior of a great white shark is to strike and let the prey die, not fight with it and take it down deep.

Having watched great white sharks at Isla Guadalupe for 13 years, I've seen them fight, bite each other and noticed that the smaller sharks tend to stay away from the bigger ones. Those actions always seemed to be a way to establish the pecking order and not an attempt to kill and eat the other shark. As a matter of fact, when we encountered a dead shark a number of years ago, all the other sharks stayed away from the area for a while, indicating that they weren't comfortable being in an area with a dead one of their own.

I have no problem saying that I have no idea what happened to this shark, but for the scientists to state that a "colossal cannibalistic shark" ate this individual, simply because of the temperature recording of a tag, is not very scientific at all.

This whole thing happened 9 years ago. So why is this all over the news now? Well, according to People, The Smithsonian Channel repackaged an Australian documentary called The Search for the Ocean's Super Predator into another doc called Hunt for the Super Predator.

So all this is done to promote a "documentary" by the Smithsonian channel. Why am I not surprised that after "Nat. Geo" and "The Discovery Channel" they are just going after sensational headlines to boost their ratings as well. Let's just scare the heck out of people by letting them believe that there are monsters lurking in the Ocean. It's not like people don't have an irrational fear of sharks already. It's not like they are killing sharks based on this irrational fear. No, they need to stoke that fear so that they can sell their stupid "documentary". Damn the consequences!

Martin Graf
Shark Diver
About Shark Diver. As a global leader in commercial shark diving and conservation initiatives Shark Diver has spent the past decade engaged for sharks around the world. Our blog highlights all aspects of both of these dynamic and shifting worlds. You can reach us directly at staff@sharkdiver.com


Megalobomb said...

I do not doubt that the tag was eaten by something else if the temp/depth profiles are true. The tag being eaten does not mean the entire shark carrying that tag does. Too often researchers who use tags forget that all the information is from the tag - not necessarily the animal itself.

Since the animal they tagged was a massive female white shark - it is more likely (but still pretty unlikely) that this tag was eaten during a mating hold.

Or the f'in thing just fell off! :)

Shark Diver said...

That's the thing, we just don't know. Also, if the shark was indeed eaten, wouldn't the temperature of the tag slowly increase, since the meat it was attached to would be considerably cooler than the stomach temperature and would cool it?

Megalobomb said...

Yep, the temperature would drop then increase (during digestion) then level out afterwards i.e. salmon sharks.