Saturday, June 7, 2014

Nine-Foot Great White Shark Eaten by Unknown Sea Creature

Gizmodo’s James Baker highlights Smithsonian‘s story of a tagged nine-foot (2.7m) great white shark whose electronic tag washed up on the beach. When scientists checked the data, they discovered a terrifying sequence of events: the tag had been dragged 1,900 feet (580m) below the surface, then eaten—achieving a 78°F temperature, 32°F higher than a great white shark’s normal body temperature. So this raises a reasonable question: what could possibly eat a nine-foot great white shark?

Conventional wisdom would suggest that it was an orca, obliviously gobbling up the tag while foraging for shark livers. They’re large enough—typically two to three times the size of the missing shark—and they have a well-documented history of hunting great white sharks. But the trouble with this theory is that as far as we know, orcas never go that deep; they typically stay near the surface, with the deepest recorded dive measuring 850 feet (259m) under controlled conditions. So if this was an orca, we have a new record.

Another possibility, raised by several Gizmodo commenters, is that the shark itself was attacked or killed near the surface of the water, dislodging the tag, which was then separated from the shark, dragged underwater, and eaten. The problem with this theory is that great white sharks are lamnoid sharks, which means that their body temperature tends to run slightly warmer than the surrounding water. If the tag and/or surrounding tissue had been removed from the shark before it was consumed, the tag would have presumably recorded an abrupt temperature drop prior to the temperature increase. It didn’t. Something dragged the nine-foot, still-living shark more than a third of a mile underwater, then ate the tag.
Could another great white shark have done it? Possibly, but that’s not likely; assuming the tag was lodged in muscle tissue, it would have been 7-9°F warmer than the surrounding water. Prior to the temperature shift, the tag recorded a temperature of 46°F; this would suggest a rather chilly water temperature of 37 to 39°F. The temperature range of a great white shark’s belly under these circumstances would be 13-25°F warmer than the surrounding water temperature, somewhere between 52°F and 64°F. The temperature recorded in whatever it was that ate the shark was 78°F.
Any ideas, readers?

Source: MU

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