Wednesday, March 06, 2013

The Mystery of Megamouth

The Mystery of Megamouth

Marine biologists have rarely been stunned by a new species the way they were absolutely thrilled in 1976 when a Navy vessel cruising off Hawaii came up with a weird-looking and totally unknown fifteen-foot shark tangled in its sea anchor. Megachamsa pelagios proved to be not only a new species but the sole member (so far as we know) of a new family. The shark is a harmless filter feeder with an oversized head and a gaping mouth which turns down sharply at the corners, giving it a perpetual grimace. It's a chunky, slow-swimming, shy creature, hardly fitting the usual picture of a shark at all.

It was eight years before a second specimen was netted. Four more turned up through 1990, including one in Australia and two in Japan. The 1990 shark was was caught alive off California. The 1200-pound fish was measured (sixteen feet, three inches), photographed, and finally released with two miniature transmitters embedded under its skin. These revealed the animal is a vertical migrator, rising and falling every day in conjunction with its food, a layer of tiny animals called zooplankton, strained out by 236 rows of very small teeth. At night the shark remains at a relatively shallow depth of about 40 feet. At dawn, it descends to 500 feet or deeper and stays there all day. This behavior, unknown in any shark until now, undoubtedly played a role in the megamouth's avoiding human contact for so long. We are now up to 54 specimens, including a 2009 catch  netted 200 meters down.

But that hasn’t solved the mysteries around this species. Where was it for so long? This fish wasn’t just unconfirmed. It was unguessed-at. There were no unexplained sightings, no accidental nettings, no identification of corpses found ashore. There were no stories or legends among Pacific islanders, even though the washed-up specimens found since 1976 show it does occur relatively close to coastlines. Why had it never encountered humanity, vertical migrator or not?

Logically, if there specimens washed ashore since 1976, they must have washed ashore before that, also. Presumably some were in remote localities, while others were just cut up for bait or otherwise disposed of. But it’s still weird. Several dozen have now been found or caught, dead or alive.  And before 1976, nothing, not even fossils of possible ancestors. 
The megamouth was the biggest wholly new marine animal (as opposed to the recent beaked whales and dolphins, of which we had some sightings or other clues) found in the last few decades. We've gone 37 years without a big animal that was quite as surprising. But its remarkable tale should make us all keep our eyes on the oceans.

Other big things may still be there….

Megamouth (photo NOAA)

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