New Caledonian Manta Breaks All-Time Deep Diving Reef Manta Record
Researchers studying the reef manta ray population of the south-western Pacific islands of New Caledonia have observed one of the animals breaking the known world record for deep diving reef mantas, according to a paper recently published in the online journal PLOS ONE.
Reef manta rays (Mobula alfredi) are the smaller of the two known species of manta, with a wingspan – or 'disc-width' – of up to 5.5m at their largest, and tend to inhabit shallow coastal waters where they are often observed by divers and snorkellers feeding and cleaning. There have been many studies into the behaviour and range of reef manta, but little is known about their activities when they move further from shore and into deeper waters – particularly during the night.
Previous research has shown that reef manta regularly dive to 150m or more, with one individual in a 2014 study reportedly reaching a depth of 432m. The New Caledonia study, the first to be conducted in the region, used data from nine Pop-up satellite archival tags (PSATs) and discovered that all of the tagged animals made regular dives to a depth of 300m, with one recording the record-breaking depth of 672 ±4m.
Most of the deep-diving was reported at night, suggesting that the manta were feeding on a source of plankton gathered at that depth, and the authors theorised that perhaps the supply of plankton nearer the surface was inadequate to support the population on a sustainable basis.
Studies of the second species of manta, the oceanic or giant manta ray (Mobula birostris) have observed the larger species, with a disc-width of over 7m in mature individuals, diving to depths of over 1km. The deep-water habitat and range of the oceanic manta is, however, much greater than that of the reef manta, and they are less regularly observed at close to the shore.
Populations of both reef manta and their larger oceanic cousins are in decline worldwide, mostly due to overfishing and as accidental bycatch. Mantas are highly prized by the Chinese market for their gill-rakers, the organ which filters oxygen from the water and which is thought to help purify the blood – a so-called 'traditional' remedy which has been in existence for less than twenty years.
Both species are currently listed as vulnerable to extinction by the IUCN Red List. That the new study increases the known depth range of reef manta by more than 200m demonstrates – yet again – how little we know about these fascinating, gentle giants.
The study 'Diving behavior of the reef manta ray (Mobula alfredi) in New Caledonia' by Hugo Lassauce et al of the University of New Caledonia was published on 18 March in the open-access journal PLOS ONE. The study can be read at journals.plos.org/plosone/article?id=10.1371/journal.pone.0228815