Elusive megamouth shark snared in Mexico

From Cosmos Magazine: Elusive megamouth shark snared in Mexico

ENSENADA: One of the rarest known species of fish, the megamouth shark, has been caught by fishermen in Mexico for the second time in five years.

Only 51 specimens of the elusive deep-water shark have ever been caught or sighted since the discovery of the species in Hawaii in 1976. So far, megamouths have appeared in the Pacific, Atlantic and Indian oceans, mostly near Japan and Taiwan, but also in places as diverse as Australia, Ecuador and South Africa. Yet only one has been ever captured alive, in 1990.

The newly caught shark, a three-metre male deceased juvenile, was captured near the western Baja peninsula coast, in a region called Bahía de Vizcaíno, which is about a seven-hour drive south of San Diego, California.

It was caught by the same fishing vessel that in 2006 captured another megamouth specimen in Vizcaino bay, which has led Mexican scientists to believe that the megamouth could be a seasonal visitor to the Baja Peninsula.

"Although there is few scientific data collected, local fishermen assured us that they've caught other, even bigger megamouth sharks before, so we believe this might mean this species can be part of the shark population that roams the western coasts of Baja," said Omar Santana, a researcher for Ensenada-based CICESE science institute.

One of a kind

Scientists consider the megamouth a one-of-a-kind shark: despite the fact that adults can reach a length of over six metres, making it the largest deepwater fish in the world, it is a slow swimmer and, unlike its most famous Great White relative, feeds by filtering water.

With a brownish-black colour and a large head, and a mouth with protruding jaws unlike any other shark species known, it has been classified into its own family, Megachasmidae, under the scientific name Megachasma pelagios.

The new specimen was taken to Ensenada, Mexico, where it was photographed and sliced in order for Scripps Institution of Oceanography and Mexican researchers to study the structure of its muscles and gills.

"Sharks have two muscles, white and red. Some have the red muscle in the outer part of the body. This is a very rare opportunity to study the megamouth's speed, how it moves and where it lives," said Santana.

Important area for megamouths

Little is known about the shark's reproduction and feeding, other that it usually dives up to 500 m in search of plankton and krill, a microscopic shrimp species.

Despite its huge head, its teeth are tiny, which researchers suggest is a means of absorbing and filtering large amounts of water.

Even though the megamouth is very rare, the capture of this shark in the Baja Peninsula is an indicator of how ecologically important the region is. Santana hopes this will encourage the Mexican authorities to improve marine species management and better regulate commercial fishing in the area.