Mantas of maldives part 1

Mantas of the MaldivesPart 1: Introduction to Manta ecology and

distribution

By Dr. Anne-Marie Kitchen WheelerProject Founder

Manta Ecology Project

Two species of manta ray:

Manta birostris (Walbaum 1792) (MB)

Common name: GIANT or OCEANIC MANTA

Manta alfredi (Krefft 1868) (MA)

common name ALFRED or REEF MANTA

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Another species? A third species has been proposed which may be a sub-species of MB or may be a new species by it’s limited range (Marshall et al. 2009).






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Another species? A third species has been proposed which may be a sub-species of MB or may be a new species by it’s limited range (Marshall et al. 2009).

Both species are observed in the Maldives however MB is much rarer (12 vs 2220 individuals recorded Manta Ecology Project database Jan. 2014)

Manta birostris (MB) Manta alfredi (MA)

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TEETH ON:o UPPER JAWo LOWER JAW

TEETH ON:o LOWER JAW

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There are black variants of each species but are exceedingly rare in Maldives and only black MB have so far been reported. Black MA are common is other tropical island areas (up to 50% of MAs may be black variant)

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Manta rays can be individually identified from their ventral markings

Marks in central and abdominal areas are used to identify individuals (Kitchen-Wheeler 2010, Marshall et. al 2009)

A trained observed will quickly appreciate that markings vary between individuals and that markings are unique

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Manta rays can be individually identified from their ventral markings

Visual identification can be used instead of tagging or physically marking individuals

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Manta Lifecycle (MA)

The age to which mantas live is still not fully understood but a

Male’ based manta ray known as Brenda is known to be at least 40 years old.

One of the oldest Mantas in the world?

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Age and growth studies in other elasmobranchs have been based

on ring (or band) measurements of vertebrae sections but these have not been found/reported in manta rays.

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Examples of known longevity of other elasmobranchs in the wild include the common spiny dogfish Squalus acanthias

(Linnaeus 1758) achieving 65-70 years and grow to 170 cm total length.

It is likely that manta rays live as long.

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Manta Lifecycle

Female mantas give birth to fully formed live young. Examples

born in aquaria measured 1.92-1.96 m disc width (DW). Live young in the wild have been observed at around 1 m DW. A

wild birth has not been observed.

Large energy investment that the parent manta put in the offspring.

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Manta Lifecycle

Pregnancy last around 12.5 months

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Manta Lifecycle

Heavily pregnant females are frequently seen at cleaning stations nearby large sheltered lagoons

e.g. Rasfari

Juveniles are frequently observed in sheltered lagoons used by safari and fishing boats for anchorage so it is likely

that birth occurs in the lagoons.

This subject is a topic of current research

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Diurnal Activity

From dawn and throughout daylight hours mantas may be

observed at cleaning stations and feeding areas at shallow

reef areas. They are also observed hovering in current in channels and locations with strong water flow.

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Diurnal ActivityFrom dawn and throughout daylight hours mantas may be

observed at cleaning stations and feeding areas at shallow reef areas. They are also observed hovering in current in channels

and locations with strong water flow.

After dusk mantas rays are commonly observed still feeding at inshore areas and can be attracted to feed in shallow lagoons.

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Diurnal ActivityFrom dawn and throughout daylight hours mantas may be observed at cleaning stations and feeding areas at shallow reef areas. They are also

observed hovering in current in channels and locations with strong water flow.

After dusk mantas rays are commonly observed still feeding at inshore areas and can be attracted to feed in shallow lagoons.

At night they travel offshore to feed in deep water (50-200

m) as zooplankton rises.

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Diurnal Activity

This pattern has been shown from independent study in Okinawa prefecture (Japan), Komodo (Indonesia) and various Hawaiian islands and suggested by initial study in the Maldives

(Yano et al. 2000; Clark 2008 ; Dewar et al. 2008). Similar behaviour has also be shown by MB (Rubin et al. 2008).

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Distribution

Red: MB circumtropical plus temperate

Blue: MA Indo-Pacific tropical

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Distribution

Red: MB circumtropical plus temperate

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Distribution

Blue: MA Indo-Pacific tropical

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Distribution

MB has been reported from offshore islands (Revillagigedos/Mexico, Galapagos/Ecuador, French Polynesia, Okinawa prefecture Southern Japan, Maldives, and off most continental coastlines.

In areas where it is sighted regularly it is only reported seasonally, in association with local increases in plankton productivity.

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Distribution

MA has been reported from Maldives, Hawaii, Okinawa prefecture islands, throughout Indonesia, Malaysia and French Polynesia.

It is reported from continental coastlines including E. Africa and Australia in the Indo-Pacific but is absent from the western Atlantic and very rarely reported from W. Africa.

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Distribution

MA is reported year round at the majority of locations where sighted and at most locations the local

populations are considered resident.

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Thank you for your attentioncontact details: [email protected]

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Mantas of maldives part 1

Education

Transcript of Mantas of maldives part 1