What is the total number of mature individuals? How was this figure derived?
Identify important populations necessary for the species’ long-term survival and recovery.
Estimates of total population size for M. alfredi are very difficult to assess due to the migratory nature and global distribution of the species (Couturier et al., 2012). Regional population size estimates using sight-resight data in Mozambique and Hawaii showed that regional populations are small (less than 900 individuals) (Deakos et al., 2011; Marshall et al. 2011b). In contrast, population estimates of M. alfredi at key aggregation sites in the Maldives archipelagos ranges between 181 and 562 individuals, while the population for the entire Maldives, where several protection and conservation acts were enacted to protect the species, was estimated between 9,677 individuals (Kitchen-Wheeler et al. 2011) and 5000 (XXXX XXXX, unpubl data). Minimum numbers of M. alfredi individuals identified are provided in Kashiwagi et al. (2011) for other locations. Apart for the Maldivian population (n=1835; Kitchen-Wheeler et al. 2011), all minimum numbers of individuals are less than 700 individuals per location. To date, no interaction between regional populations has been found and dispersion of individuals is likely to be restricted by bathymetric features and/or regional ocean circulation patterns, isolating the different sub-populations (e.g. Hawaii, Deakos et al 2011).
In eastern Australia, the minimum number of M. alfredi identifiedbetween Osprey Reef and South Solitary Island is 620 (XXXX XXXX, unplubl. Data, data collected between 2008-2012).
In Western Australia the metapopulation of M. alfredi is thought to be between 1200 – 1500 individuals, with 560 individuals identified within Ningaloo Marine Park (XXXX XXXX unpubl. data).
b. As the Australian populations are currently unaffected by directed fisheries, we argue that their protection contributes significantly to maintaining the global population. Experts consulted on this application agree that the Australian population, based on current evidence, is currently one of the world’s healthiest and concur that the conservation of this population is not only important for Australia, but globally. However, the authors of this application acknowledge that this is currently speculation, as proper population size estimates over several years are required to support this statement. Important populations that contribute to the species’ long-term survival and recovery include the Queensland (e.g. Lady Elliot reef, Musgrave Reef, North Stradbroke Island, Osprey Reef), Western Australia (Ningaloo Reef, Coral Bay) and New South Wales (Solitary Islands, Byron Bay) populations.
POPULATION TREND
What is the population trend (PAST to CURRENT) for the entire species? Is the population trended increasing or decreasing, or is the population static? Provide relevant data sources.
Is this trend likely to continue, or are there any data which indicate FUTURE changes in population size? Provide relevant data sources.
Does the species undergo extreme fluctuations in the number of mature individuals?
a) Manta rays are targeted by fisheries in some parts of the world. A such, population reduction appears to be very high in several regions; up to as much as 80% over the last three generations (approximately 75 years), and globally the species is believed to have declined by >30%. In some region, manta ray populations have collapsed due to directed fisheries (e.g. Anon 1997; Alava et al. 2002). The population trend for M. alfredi is stated as ‘decreasing’ by the IUCN Red List. (Marshall et al., 2011a).
b) Manta ray gill rakers are of high value on the international market. The rising demand by Asian market in these manta ray products has led to a considerable rise in unregulated fisheries targeting M. alfredi in several parts of the world (see Couturier et al. 2012). In some regions, over 1500 manta rays can be caught per year, a number that is considered unsustainable due to the conservative life history of the species. Particularly threatening to M. alfredi is the fact that some fisheries harvest individual manta rays in large numbers at critical habitats or aggregation sites (Anon 1997; Marshall et al. 2011a; Couturier et al. 2012). The species is also caught in artisanal fisheries for food, as by catch in large-scale fisheries, shark control programs and bather protection nets (Marshall et al. 2011; Couturier et al. 2012).
c) This species is not recorded as undergoing natural extreme population fluctuations as it is a long-lived, slow-growing, k-selected species (Marshall et al. 2011a).
Identify and explain any quantitative measures or models that address the probability of the species’ extinction in the wild over a particular timeframe.
Sustained pressure from directed fishing and by-catch is likely to cause rapid decline in sub-population abundances and due to the low fecundity and long life span of M. alfredi, sub-populations do not have the capacity to recover from a depleted state (Alava et al., 2002; Mohanraj et al., 2009; Marshall et al. 2011a). The isolation, low immigration rates and reproduction rates of manta rays impend on the population’s capacity to recover from the depleted state imposed by these fisheries (Marshall et al. 2011a; Couturier et al., 2012) . Of particular concern is the fact that fisheries harvest individual manta rays in large numbers at critical habitats or aggregation sites (Anon 1997; Marshall et al. 2011a; Couturier et al. 2012).
Although global extension risk of the species cannot be assessed at this stage, M. alfredi is highly vulnerable to regional extinction in areas where the species is fished. A study of an Indigenous community in Indonesia showed numbers of animals caught went from up to 360 per annum, down to zero; essentially a local extinction (Barnes, 2005).
Geographic Distribution
GLOBAL DISTRIBUTION
Describe the species' known or estimated current and past global distribution (include a map if available). Does the species exist in an EPBC Act listed ecological community?
M. alfredi occurs along the coastal area of the following countries (Figure 2):
Australia (West Australian, Northern Territory, New South Wales and Queensland coastal zones); British Indian Ocean Territory (Chagos Archipelago); Cape Verde; Christmas Island; Cocos (Keeling) Islands; Cook Islands (Cook Is.); Djibouti; Egypt (Egypt (African part), Sinai); Fiji; French Polynesia (Society Is., Tuamotu); Guam; India (Andaman Is.); Indonesia (Bali, Irian Jaya, Jawa, Sulawesi); Japan (Nansei-shoto); Madagascar; Malaysia; Maldives; Marshall Islands; Micronesia, Federated States of; Mozambique; New Caledonia; Northern Mariana Islands; Oman; Palau; Papua New Guinea (Bismarck Archipelago, North Solomons, Papua New Guinea (main island group); Philippines; Saudi Arabia; Senegal; Seychelles (Seychelles (main island group); South Africa (KwaZulu-Natal); Spain (Canary Is.); Sudan; Thailand; United States (Hawaiian Is.) and Yemen (Kashiwagi et al. 2011; Marshall et al. 2011a; Couturier et al., 2012).
EXTENT OF OCCURRENCE within Australia
NOTE: The distribution of the species within Australia is assessed in two ways, the EXTENT OF OCCURRENCE and the AREA OF OCCUPANCY. The two concepts are closely related, and often confused. Therefore, before you answer this question, please see the definitions and explanatory material in Attachment A.
What is the CURRENT extent of occurrence (in km2)? Explain how it was calculated and provide relevant data sources.
Has the extent of occurrence changed over time (PAST to CURRENT)? If so, provide evidence.
Does the species undergo extreme fluctuations in the extent of occurrence? If so, provide evidence.
a. The current extent of occurrence in Australia is calculated as 6,780,364 km2 (Figure 3). They can be found as far south as Albany in Western Australia up and around to Sydney Harbour in New South Wales, from coastal zones stretching through to the continental shelf.
This was calculated by using the CSIRO software “image J”, in which the scaled Google Earth image was defined as the “area contained within the shortest continuous imaginary boundary which can be drawn to encompass all the known, inferred or projected sites of present occurrence of a species, excluding cases of vagrancy used as a guide to estimate the area in which the manta rays inhabit”. The known locations were connected in a dot to dot fashion with the outer edge being defined as the shelf edge (the 200m depth bar).
b. There is currently no evidence for change within Australian waters as population numbers are only just being calculated. Without this baseline data, there is no ability to detect changes in extent of occupancy. However, there is genuine concern in Western Australia, as many of the individuals there appear to migrate across international boundaries and into targeted fishing grounds to the north (XXXX XXXX unpubl. data).
c. In the case where the manta rays are protected from commercial fisheries and other human impacts then it is predicted to remain stable. However, the current extent of occurrence in eastern Australia is suggested to be linked with the circulation pattern of the East Australian Current. With climate change predicted to impact on the ocean circulation, the future extent of occurrence of manta rays is likely to be impacted and changed, however, it is not possible to determine to what end.
d. In eastern Australia, M. alfredi mostly occurs within southern aggregation sites (i.e. south of Lady Elliot Island) from spring to early autumn, while the species is seen in high numbers at Lady Elliot Island during late autumn-winter months (Couturier et al. 2011). The seasonal fluctuations in the extent of occurrence is part of the seasonal migration of the species that is likely to be influenced by the East Australian Current circulation patterns (Couturier et al. 2011).
AREA OF OCCUPANCY
NOTE: The distribution of the species within Australia is assessed in two ways, the EXTENT OF OCCURRENCE and the AREA OF OCCUPANCY. The two concepts are closely related, and often confused. Therefore, before you answer this question, please see the definitions and explanatory material in Attachment A.
What is the CURRENT area of occupancy (in km2)? Explain how it was calculated and provide relevant data sources.
Has the area of occupancy changed over time (PAST to CURRENT)? If so, provide evidence.
Is the area of occupancy expected to decline in FUTURE? If so, provide evidence.
Does the species undergo extreme fluctuations in its area of occupancy? If so, provide evidence.
The current area of occupancy is calculated at approx 29,458 km2 in eastern Australia (Figure 4) and 76,012 km2 in Western Australia (Figure 5). These figures were calculated using techniques described above using Image J – however this time drawing an elliptical area around known manta aggregation spots including - Torres Strait Is, Osprey Reef, Capricorn Bunker group (with Heron Is at the centre), Lady Elliot Reef, Wolf Rock, North Stradbroke Island, Byron Bay (around Julian rock), Solitary Islands Marine Park and Sydney Harbour in eastern Australia (Figure 4) plus an additional 16 identified locations in Western Australia (Scott reef, Rowley shoals, Port Headland, Pt Sampson, Dampier Archipelago, Montebellos, Exmouth Gulf, Ningaloo, Monkey Mia, Dirk Hartog, Geraldton, Abrolhous, Cervantes, Jurien Bay, Perth and Albany) (Figure 5). This is based on both publications and unpublished data from acknowledged experts in the field (Couturier et al 2011, XXXX XXXX unpub data, XXXX XXXX unpub data).
As mentioned in section 22, baseline surveys have only recently begun for this species, so it is not possible at this stage to provide evidence for change in population over historical time.
While several of the recognised manta ray aggregation sites are currently protected within marine park areas, a large portion are not, or are zoned in such a way that little to no protection is credited to the species. Examples of this include Torres Strait Island, North Stradbroke Island and Solitary Islands (in NSW).
Yes, the numbers of species fluctuate widely depending on season. For example, very few, to no manta rays are found south of the Capricorn Bunker Group of the GBR during the Australian late-autumn and winter (May to mid Oct). Conversely, numbers of manta rays sighted at Lady Elliot Reef during that same time considerably increases (Couturier et al 2011, Jaine et al in press).
