Megamouth sharks prove internal egg theory

The rarely seen megamouth shark and her pups (NMP Zoology Division / Annabelle Lapitan, Agricultural Technologist of LGU-Dipaculao)
The rarely seen megamouth shark and her pups (NMP Zoology Division / Annabelle Lapitan, Agricultural Technologist of LGU-Dipaculao)

The first proof has emerged than one of the world’s biggest sharks is “ovoviviparous” – meaning that its embryos grow in eggs, nourished by the yolk, within the mother before the young sharks hatch and are born live and independent.

Unfortunately it took a dead specimen of the rarely seen shark to make the case, after a 5.6m megamouth (Megachasma pelagios) that had been pregnant with seven pups was found washed ashore in Aurora province in Central Luzon in the Philippines in mid-November. 

The mother and a pup that had been born and was found beside her were examined under the remote supervision of an expert from Marine Wildlife Watch of the Philippines. The remaining pups were taken to the National Museum of the Philippines for detailed examination and preservation.

Necropsy on the megamouth sharks (NMP Zoology Division / Annabelle Lapitan, Agricultural Technologist of LGU-Dipaculao)
The megamouth shark pups (NMP Zoology Division / Annabelle Lapitan, Agricultural Technologist of LGU-Dipaculao)
A megamouth shark (Shark Research Institute)
A megamouth shark (Shark Research Institute)

The deepwater megamouth shark species was discovered only in 1976. Typically just over 5m when fully grown (females are larger than males) it is by far the smallest of the three filter-feeding sharks. The others are whale sharks and basking sharks, both of which are ovoviviparous.

The Philippines is regarded as its most important habitat after Taiwan, though most reports are of dead specimens that had either been stranded or caught as bycatch. According to the Sharkman’s World blog site, which records all megamouth shark and other sightings, the one in Aurora was the 284th made to date.

Megamouth sharks spend their days at depths typically down to around 1km, surface-feeding only by night.

Also on Divernet: Rare megamouth shark recorded

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