But Killer Whales don't pray on adult Blue Whales, they only pray on the young whales, and from Wikipedia's definition of apex predator... The only natural (non-human) predator that has ever been recorded attacking a Blue whale is packs of killer whales, or Orcas. It is highly unlikely that they would ever attempt to take down an adult blue whale, do to the sheer difference of scale between the two whales. But Groups of Orcas have been known to attack and kill young blue whales. http://www.blue-whale.info/Predators_of_the_Blue_Whale.html
From Wikipedia on blue whales: "The whales' only natural predator is the Orca.[41] Studies report that as many as 25% of mature Blue Whales have scars resulting from Orca attacks.[24] The rate of mortality due to such attacks is unknown." So, it seems that orcas do attack mature whales. Well, it's a little uncertain phrasing but they do label orcas as a "natural predator," which seems to preclude blue whales from being an apex predator.
But those scares may have been from attacks when the whales were young. Also, doesn't an attack have to be fatal in order to consider it predatory? I can't find a single account of an Orca killing an adult Blue Whale.
Agreed, that's why I said it was uncertain. Probably. On the other hand, animals rarely attack others when they have no expectation of success. I'm not a marine biologist, so I can't say why, how often and with what success rate orcas go after mature blue whales, but if blue whales have a recorded natural predator, I'm claiming victory. Megalodon ftw.
