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Threatened Species Nomination Form - Manta alfredi

2012 Assessment Period - Manta alfredi

Species Information

TAXONOMY

Provide detail on the species' taxonomy, including whether or not it is conventionally accepted.

Kingdom: ANIMALIA

Phylum: CHORDATA

Class: CHONDRICHTHYES

Order: RAJIFORMES

Family: MOBULIDAE

Scientific Name: Manta alfredi

Common Name/s: English Reef Manta Ray, Coastal Manta Ray, Inshore Manta Ray, Prince Alfred's Ray, Resident Manta Ray (Marshall et al. 2009).

Indigenous Name/s: No known Indigenous Names.

Manta alfredi has recently been described (Marshall et al 2009). Prior to this publication, the genus Manta was considered to be monospecific, with M. birostris having a worldwide distribution. This recent taxonomic revision recognised at least two distinct species, M. birostris and M. alfredi, and a putative third species, M. cf. birostris (Marshall et al. 2009). M birostris is also found in Australian waters (reported semi regularly in Western Australia), but in much lower population numbers relative to M. alfredi (XXXX XXXX, unpubl. data; XXXX XXXX, unpubl. data).

DESCRIPTION

Describe the species, including size and/or weight, social structure and dispersion (e.g. solitary/ clumped/ flocks), and give a brief description of its ecological role (e.g. is it a keystone or foundation species, or does it play a role in ecological processes such as seed dispersal or pollination).

Species Description:

M. alfredi is a large filter-feeding elasmobranch reaching up to 5000mm disc width (DW) and is circumglobally distributed in tropical and subtropical waters (Figure 1) (Couturier et al., 2012). DW at maturity for the species is estimated to be 2700 3000mm for males and 3700-3900mm for females (Clark, 2010; Deakos, 2010; Marshall & Bennett, 2010). Manta rays have two cephalic lobes on the front of their heads that are used to help the water flow into their mouth. Their broad mouth is located at the distal end of the head with a single band of minute teeth within the upper jaw. Their eyes and spiracle valves are located on the side of their heads. They have a single small dorsal fin near the tail, and are lacking a stinging spine. They have five gill openings ventrally located. Their gills are modified into complex sieving plates through which they extract oxygen but also filter their planktonic food from the water. Manta alfredi is an ectothermic species, however, studies have shown that Manta species have a counter current heat exchanger system, allowing regulation of their internal brain temperature (Alexander 1996).

Social Structure and Dispersion:

M. alfredi predictably aggregates at particular locations. These aggregations are associated with seasonal availability of food, the circulation patterns of currents, sea water temperatures, mating behaviour and cleaning station visitation. Reef mantas are regularly present at cleaning stations in shallow reefs and costal feeding grounds during daylight hours and move to deeper, offshore waters during the night (Anderson et al., 2011; Clark, 2010b; Couturier et al., 2011; ). Maximum movement recorded for Manta alfredi individuals is currently slightly over 500 km (Couturier et al., 2011) .

Ecological role:

M. alfredi is a planktivorous species, feeding low down on the food chain (Couturier et al 2012, Jaine et al 2012). Manta rays are an important indicator species in regards to impacts caused by loss of climatic habitat caused by anthropogenic emissions of greenhouse gases, as their planktonic food source is highly sensitive to environmental changes. Climate change influences the abundance, distribution and phylogeny of the plankton (Hays et al. 2005; Richardson, 2008), which most likely directly impact manta ray distribution and behaviour.

M. alfredi provide important mid water habitat for many species of fish, including several commercially important species of trevally, black king fish, plus remoras and pilot fish (XXXX XXXX, unpubl. data). Finally they provide a food source for a large range of species from the cleaner wrasse, moon wrasse and butterfly fish that consume parasites and dead flesh removed from individual manta rays, through to medium to large sharks and orcas which have been observed consuming large bites of flesh through to consuming the entire animal (Fertl et al., 1996; Homma et al., 1999; Ebert, 2003; Visser and Bonoccorso, 2003; Marshall and Bennett 2010; Deakos et al., 2011, Couturier et al., 2012)

BIOLOGY

Provide information on the species' biology, including its life cycle, generation length, reproductive and feeding characteristics and behaviours.

The information available on the biology of M. alfredi is currently limited. Here we present all known and recorded biological data. Detailed information can be found in Couturier et al. 2012.

Life Cycle:

M. alfredi has longevity greater than 31 years (Clark, 2010). The species is aplacental viviparous, with embryos developing within the uterus. Embryos initially feed on yolk and are later nourished by uterine milk (Wourms, 1977). The gestation period is between 12 and 13 months, with an occasional resting period of two of more years between pregnancies (Marshall and Bennett 2010a). Males reach sexual maturity between the ages of three to six years (Clark 2010). Female sexual maturity ages are unknown. Females usually give birth to only a single pup, though cases where two pups have been birthed have been infrequently recorded (Clark, 2010; Marshall & Bennett, 2010). Limited data is available regarding generation lengths but is suspected as being 25 years (Marshall et al. 2011a).

Natural Mortality:

Natural predation rate on adult M. alfredi is believed to be low. Sharks are suspected as the most common predators, though many attacks are non-fatal (Marshall and Bennett, 2010b; Deakos et al. 2011).

Reproduction:

Critical knowledge gaps still exist for M. alfredi reproduction. Manta rays employ internal fertilization to reproduce (Wourms, 1977) and the mating process consists of a complex ritualised sequence that involves chasing, biting, copulating, post-copulation holding and separation; requiring many kilometres of space to perform these behaviours (Marshall and Bennett 2010a).

Feeding:

Manta rays are planktivorous and their modified gills are used to sieve plankton out of the water (Bigalow and Schroeder, 1953; Cortes et al., 2008). The species feed by swimming with an open mouth allowing a water flow through a gill-raker apparatus; a behaviour called ram filter feeding (Sanderson and Wassersug, 1990; 1993, Cortes et al., 2008). Other observed behaviours include chain feeding, where aggregates of individuals follow each other in a circular movement creating cyclonic motions (Law, 2010).

Diet:

Based on one stomach content analysis, M. alfredi was confirmed to feed on zooplankton (Whitley, 1936). Seasonal aggregations of other mobulid rays have been recorded as coinciding with the peak abundance of animal prey species ( Whitley 1936; Notarbartolo di Sciara, 1988). 'Loss of climatic habitat caused by anthropogenic emissions of greenhouse gases' is a listed key threatening process that could impact their seasonal diet (Couturier et al 2012). As oceanic temperatures are expected to warm by 23 C by 2070 (IPCC, 2007), the zooplankton community is likely to respond in terms of changes in abundance, timing and productivity both globally and locally (Edwards & Richardson, 2004; Richardson & Schoeman, 2004). As such, both the feeding grounds and diet of M. alfredi are likely to be affected by loss of climatic habitat caused by anthropogenic emissions of greenhouse gases.

Movement:

Although the knowledge on the movement patterns of M. alfredi is still in its infancy, the species is known to migrate relatively long distances, moving between productive areas and aggregating at specific sites (Couturier et al., 2011). Individuals can travel up to 70km in a single day (van Duinkerken, 2010). Photographic Identification studies have shown that seasonal migrations of at least 500km occur between known aggregation sites (Couturier et al., 2011).

HABITAT

Describe the species habitats and what role they play in the species' life cycle. Include whether or not the species is associated with, or if it relies on, a listed threatened ecological community or listed threatened species?

M. alfredi is commonly sighted inshore, around coral reefs and rocky reefs in coastal areas. Long-term sighting records suggest that this species is mostly resident to tropical and subtropical waters (Marshall et al 2009; Marshall et al., 2011a). The species has been recorded as being sympatric in some locations and allopatric, with the Giant Manta Ray M. birostris, in others (Kashiwagi et al., 2011).

M. alfredi predictably aggregates to particular locations such as Lady Elliot Island, North Stradbroke Island and Byron Bay in eastern Australia, for which they display a high degree of site fidelity (i.e. visit the same site over time) and residency (Couturier et al. 2011; XXXX XXXX, unpubl data)). Species residency is also recorded along the Western Australian coast line, with populations recorded in Ningaloo Marine Park (Figure 4) (XXXX XXXX, unpubl. data,). Aggregation sites for M. alfredi in Australia have been identified as feeding areas, cleaning stations, reproductive sites and potential migratory landmarks (Couturier et al. 2011). As such, aggregation sites are strongly believed to represent critical habitats for this species.

Long term site fidelity has been recorded for M. alfredi in other parts of the world, such as Indonesia (Dewar et al. 2008), Mozamb

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