Making a Meal out of Shark Alpha

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” ― Sherlock Holmes

The shark Alpha case from 2003, made public in 2013 and which is still perplexing numerous internet users, is fraught with problems and rife with speculation. Here's a rundown, as all videos and media reports on this case contain false or insufficient information, for all those not so familiar with the story. (If you want to jump straight to CSIRO’s explanation of events, there’s a link at the bottom of the comment.)

In September 2003, during a shark tagging event in Australia, a 3m white shark was tagged with a pop-up satellite tag (monitoring location, movement, depth, light, ambient water temperature) by scientists from the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The filmmaker Dave Riggs was hired to film this event. A few months later the tag was found washed up on the beach and sent back to CSIRO.

Data from the fully functioning tag revealed that:

a.) the tagged shark took a dive to 570m down the continental shelf of Bremer Canyon.
b) about a week later the temperature rose to around 25-26°C and remained that way for about two weeks.
 c.) the tag failed to register sunlight in that time.
 d.) the tag kept on recording various depths, until it surfaced and washed ashore.

Dave Riggs interpreted the data somewhat differently, becoming obsessed with the story for the next ten years until his first documentary The Search for the Ocean’s Super Predator in 2014 with Smithsonian Channel. Riggs claimed the shark plunged at high speed to a depth of 580m and within seconds the temperature rose to around 78°F (25,5°C.) After eight days of recording depths between the surface and ~100m, the tag was then released to the surface. Riggs came to the conclusion the tagged shark must have been eaten, proposing three possible candidates - orcas, giant squid and a white shark. At the end of the programme Riggs claimed a 16 ft white shark was responsible. There's also a sequel Super Predator from 2015 which makes even more sensational claims. Here Riggs proposed a subspecies of giant great white shark reside in the Bremer Canyon.
All media reports and Youtube videos are (loosely) based on Dave Riggs' version of events.

So, what are we to make of it all?

People interested in the story have made several proposals, including giant goliath groupers, Carcharocles megalodon, sperm whales, giant squid, orcas, some unknown (prehistoric) animal, a larger white shark, even a malfunctioning tag, or human interference, to name the most common suggestions.If we simply take the recorded tag-temperature of 25–26°C, we can already exclude several popular candidates from the list:

• sperm whales and orcas are mammals, thus would have an internal temperature of around 35–37°C (except during feeding, were the intake of cold seawater would cool the stomach for short periods of time). Although there is at least one documented case of a sperm whale with an ingested large shark and orca’s are known to hunt white sharks, the recorded temperature is simply too low for a mammal.
  
• giant squid are ‘cold-blooded’, taking on the temperature of their surroundings. Moreover, the beak and rasping radula would have made mincemeat out of the tag, rendering it useless.
  
• The Queensland Groper, Epinephelus lanceolatus, can certainly grow up to 2,7m and is a formidable predator, but, like most fish, it is cold-blooded and would certainly not have been after a 3m white shark.
  
• One of the most popular suggestions is that a giant prehistoric shark, Carcharocles megalodon, is secretly still roaming the ocean and that one ate the tagged shark. This suggestion, (as well as other prehistoric creatures like mosasaurs), is based on the alleged depth the attack took place and the idea that the tagged shark was eaten whole, thus it must have been a huge predator to be capable of such a feat. To this very day we have no evidence whatsoever that these prehistoric creatures still exist and should have, if they were still alive. Just for the record, some scientists argue C. megalodon was probably endotherm, having a warm body.
  
• Tag malfunction and human interference, although possible, don’t match the data we do have, so can be ignored as possibilites.

Is there a suitable candidate?

There is one probable candidate which fits the data in all aspects - the great white shark. It has long been known that the white shark is endotherm, with numerous field studies proving it has a stomach temperature of around 25–26°C. Also, the recorded depths after the tag was ingested suit the swimming behaviour of a white shark. (Marine mammals would need to breathe regularly.) Moreover, it is simply false to assume the tagged shark was eaten (whole) in the first place. White sharks abide by a pecking order based on size and gender, mostly avoiding conflict if possible, that is, after they are born. Still in their mother’s womb, cannibalism isn’t so uncommon.All that was needed was for another white shark to have bitten off the tag and ingested that, instead of the whole tagged shark itself. For all we know, the tagged shark may very well still be alive.

What does CSIRO have to say about it all?

This is the unheeded and mostly unknown response of CSIRO to all the speculations about this incident:https://blog.csiro.au/busting-the-megalodon-myth-did-a-3m-shark-get-eaten-by-an-even-bigger-shark/

I hope my answer to this fishy story has given some food for thought without giving you too much indigestion. Have a great day!