Maui Manta Mystery: Part Deux

As a scientist, I tend to subscribe to Occam's Razor when formulating explanations. So when I was sent images from Maui last week of Tiger sharks feeding on a dead manta stuck in a mooring line, the initial explanation offered seemed simple and plausible. The manta died or was killed by a Tiger shark and then got tangled in the mooring line. But Pauline Fiene of Mike Severns Diving wrote me today suggesting that the evidence tells a different story.

Look at the image at the top of the post. It's a big manta (Pauline actually measured the wingspan at 15 feet) resting on the bottom with the mooring ball just above it. Now this picture was taken at a depth of 115 feet. The mooring line is 7/8th inch thick and is about 80 feet in length. That's a lot of weight! The mooring ball, which normally sits 20 feet below the surface, is now down at 115 feet with the ray. If you're doing the math along with me, you must realize that it takes a significant investment of strength to pull a mooring ball and 80 feet of heavy, thick line down to 115 feet. Pauline suggests that contrary to the original hypothesis, the manta did not get tangled after it was dead.

If you have been fortunate to witness mantas performing huge underwater barrel rolls as they feed on plankton swarms, it's not a far stretch to imagine an animal accidentally becoming entangled. Frantic thrashing and rolling could result in the line winding around the body as seen in the images. While mantas breath via ram ventilation, requiring a steady passage of oxygen rich water across their gills, if entangled it's still conceivable a manta could survive for a time. Pauline explains that when she first arrived on the scene, she believes the manta was indeed still barely alive. However, one of the Tigers took a decisive bite that resulted in heavy blood loss (see below image) which apparently finished-off the manta.

Other documented cases of a manta becoming entangled in a mooring or anchor line have been documented in Hawaii and along the Mesoamerican Barrier Reef. Thanks, Pauline, for a fresh (and well reasoned) explanation. It's great to be reminded that things aren't always what they seem.