The Reef Manta Ray (Mobula alfredi) is a large (to 500 cm disc width) ray with a tropical and subtropical distribution throughout much of the Indian and Pacific Oceans in coastal and pelagic waters from the surface to 432 m deep. The global population size is not known, but some local and regional population sizes have been estimated and are mostly small, at less than 1,000 individuals, with the exception of the Maldives where the population is estimated at ~10,000. While individuals are capable of long-distance movements they do so infrequently, consequently aggregations are widely separated with low connectivity resulting in a high likelihood of local depletion. The species has an extremely slow life history, producing only 1 pup on average every 4–5 years, and consequently is likely to have one of the lowest maximum rates of population increase (median 0.032 per year) among elasmobranchs. Reef Manta Rays are targeted or taken as bycatch in artisanal small-scale fisheries, as well as taken as bycatch in large-scale industrial tuna fisheries. The meat is consumed locally and they are traded internationally due to the rapid rise of the valuable gill plate trade. Where Reef Manta Rays are protected (in over a dozen countries and territories), and hence where they are not being fished, the sighting trends appear stable. Elsewhere, however, very rapid declines in sightings records have occurred where they are targeted or caught as bycatch. For example, Reef Manta Ray sightings declined by 98% over a 15-year period (half a generation span) in southern Mozambique. Where fishing pressure is higher, the Reef Manta Ray is suspected to have declined to the point of local extinction in many places throughout much of the Indian Ocean. Globally, the suspected population reduction is 30–49% over the past three generation lengths (87 years) with further population reduction suspected over the next three generation lengths (2018–2105). The suspected past and future population reduction is based on extremely low maximum rates of population increase, current and ongoing levels of exploitation, steep decline estimates, and reduction in extent of occurrence due to suspected local and regional extinctions, offset only by stable trajectories in a relatively few well-protected areas. The Reef Manta Ray is therefore assessed as Vulnerable A2bcd+3d.

The global population size of the Reef Manta Ray is difficult to assess, but abundance trajectories have been estimated based on long time-series of sightings at diving sites. Generally, divers encounter the Reef Manta Ray with far greater frequency than the Giant Manta Ray (Mobula birostris), which is likely due to the occurrence of Reef Manta Ray in shallow coastal waters of many well-developed tourist areas. Additionally, Reef Manta Ray encounters are more reliable because they aggregate and habitually visit specific cleaning stations (Marshall 2009, Stevens 2016).

In most regions, Reef Manta Ray population sizes appear to be small (less than 1,000 individuals). Photo-identification studies and mark-recapture studies at specific aggregation sites in Hawaii (Deakos et al. 2011), Yap (B. Acker pers. comm. 10/2/2009), Mozambique (Marshall et al. 2011), Japan (Kashiwagi 2014), the east coast of Australia (Couturier et al. 2014), and Indonesia (E. Germanov pers. comm. 9/11/2018,  R. Perryman pers. comm. 8/11/2018, S. Venables pers. comm. 6/11/2018), have produced minimum estimates of 85 to 1,000 individuals. In one location, the Maldives, larger country-wide studies have produced catalogues of more than 4,000 individuals (Kitchen-Wheeler 2010, Stevens 2016). Petersen and Jolly-Seber probabilistic estimators were used to assess population size for the main aggregation areas in the archipelago with a final extrapolation of 9,677 individuals for the entire Maldives (Kitchen-Wheeler 2010).

There is low connectivity between widely separated sites and a high degree of residency, rendering Reef Manta Ray vulnerable to local depletion and regional extinction. While individuals are capable of long-distance movements, such as up to 650 km, they appear to do so very infrequently (Couturier et al. 2011, Couturier et al. 2014, Germanov and Marshall 2014, A. Marshall unpubl. data). Cross-referencing of regional photo-identification databases reveals little evidence of long-distance interchange occurring indicating a low degree of connectivity between Reef Manta Ray aggregation sites (Deakos et al. 2011, Stevens and Peschak 2016, Holmberg and Marshall 2018). Long-term studies, including those which have incorporated telemetry, suggest resident populations are common. Movement patterns suggest small home ranges and seasonal migrations (Dewar et al. 2008, Anderson et al. 2011, Couturier et al. 2011, Jaine et al. 2012, Jaine et al. 2014, Couturier et al. 2018, Setyawan et al. 2018). There appears to be a tendency for rays to visit specific sites of restricted geographical extent (Dewar et al. 2008, Perle 2011, Couturier et al. 2014, Jaine et al. 2014, Stevens 2016, Kessel et al. 2017, Couturier et al. 2018, Setyawan et al. 2018).

The trajectory of the number of individuals varies widely across the range of Reef Manta Ray, but trajectories are stable where they are protected and declining rapidly where fishing pressure is greater. The number of individuals appears stable in locations where they receive some level of protection, such as Australia (A. Armstrong pers. comm. 31/10/2018), Japan (Kashiwagi 2013), the Maldives (G. Stevens pers. comm. 10/11/2018), and inside marine protected areas in Indonesia (A. Marshall unpubl. data). Elsewhere, the number of individuals is likely to be declining in places where the species is targeted or caught regularly as bycatch. There are two estimates based on sightings-per-unit-effort. In southern Mozambique, a 98% decline in diver sighting records occurred over a 15-year period in a well-studied population (Rohner et al. 2017). In Maui, Hawaii, there has been a 94% decline in sighting records in some places where a long-term study has noted a high proportion of fishing entanglement injuries (Deakos et al. 2011, M. Deakos pers. comm. 10/11/2018). Elsewhere in Hawaii, the number of sightings has been stable (Ward-Paige et al. 2013).

Along with these sightings data, it is suspected (based on historical sightings, distribution data, and habitat suitability) that the Reef Manta Ray may have been depleted in areas where significant fisheries for manta rays exist, such as Madagascar, Tanzania, Kenya, Somalia, Pakistan, India, Sri Lanka, Bangladesh, Myanmar, China, and Indonesia. In these densely populated and heavily fished countries, fishing pressure may have more swiftly depleted resident aggregations of Reef Manta Rays. 

There are two narratives consistent with rapid local depletion and disappearance of manta rays, particularly in Indonesia. In the Alor region of eastern Indonesia, increasing international trade demand for manta ray products in the 1990s resulted in increased fishing effort with up to 2,400 manta and devilrays landed per year. Consequently, manta ray catches (including what was suspected to be the Reef Manta Ray) declined sharply in this region, forcing fishers to travel further afield to find manta rays (Dewar 2002). The Reef Manta Ray is no longer seen in this region. In East Flores and Lembata, Indonesia, manta rays (including the Reef Manta Ray) had historically been fished by indigenous villagers since 1959, with up to 360 individuals caught a year (Barnes 2005). By 1996, no mantas were being landed. 

Recently, target fisheries for the Reef Manta Ray have begun in some locations, like Dinagat Island in northern Mindanao, Philippines (Acebes and Tull 2016). Formerly, manta ray catches comprised of the Giant Manta Ray and more recently fishers claim that they now target the smaller more-resident Reef Manta Ray to supply products to Bohol during the off season. This example highlights the potential for an expansion and subsequent depletion of Giant Manta Ray fisheries to pivot toward Reef Manta Rays in the future (Acebes and Tull 2016). 

In Papua New Guinea, local declines have been noted and are attributed to fishing pressure (Rose 2008). Unspecified manta rays (some of which, based on distribution records, were likely Reef Manta Rays) were caught as non-target species in purse seine sets from 1995 until 2006. There was a distinct and significant rise in the number of manta rays caught in these fisheries in 2001, which steadily rose until 2005/2006 when sharp declines were noted in the catch (Rose 2008). 

The Reef Manta Ray is a neritic and oceanic pelagic ray typically resident in productive near-shore environments, such as coral and rocky reefs, island groups, atolls, and continental coastlines (Marshall et al. 2009). It often exhibits diel patterns in habitat use moving inshore during the day to clean and socialize in shallow waters, and then moving offshore at night to feed (Dewar et al. 2008, Van Duinkerken 2010, Jaine et al. 2014). The Reef Manta Ray is one of the largest ray species attaining a maximum size of 500 cm disc width (DW), however, it rarely exceeds 400 cm DW (Marshall et al. 2009, Deakos 2010, Stevens 2016, Lawson et al. 2017). Males mature at 270–300 cm DW and females mature at 300–350 cm DW. Reproduction is aplacental viviparous with a single large pup of 130–150 cm DW in the wild (180–190 cm DW in captivity) born every 1–7 years, with central tendency of a 4–5 year reproductive cycle (Marshall and Bennett 2010a, Deakos 2011, Kashiwagi 2014, Stevens 2016). Female age-at-maturity is 8–17 years, depending on region and food availability, and maximum age is estimated at 45 years; generation length is therefore 29 years (Couturier et al. 2014, Stevens 2016). Based on this life history, the maximum intrinsic rate of population increase could range between 0.019 and 0.046 per year (median 0.032 per year) (J. Carlson unpubl. data following methods in Dulvy et al. 2014). The species is among the longest-living rays and has an extremely conservative life history; the average Reef Manta Ray may produce only 4–7 pups during its estimated lifespan, which would contribute to its slow recovery from population reductions due to over-exploitation or other threats.

Mobulid rays, including the Reef Manta Ray, are both targeted and caught incidentally in industrial and artisanal fisheries (Couturier et al. 2012, Croll et al. 2016, Stewart et al. 2018). These rays are captured in a wide range of gear types including harpoons, drift nets, purse seine nets, gillnets, traps, trawls, and longlines. Manta rays are also caught in bather protection nets (Cliff and Dudley 2011, Department of Agriculture and Fisheries 2018). Their coastal and offshore distribution, and tendency to aggregate makes mobulid rays particularly susceptible to bycatch in purse seine and longline fisheries and targeted capture in artisanal fisheries (Croll et al. 2016, Duffy and Griffiths 2017). In particular, Reef Manta Rays are easy to target because of their large size, slow swimming speed, tendency to aggregate, predictable habitat use, and lack of human avoidance (Couturier et al. 2012). 

Mobula rays, including Reef Manta Rays, are caught in at least 13 targeted artisanal fisheries in 12 countries. Some of the largest documented fisheries have been in Indonesia, the Philippines, India, Sri Lanka, México, Taiwan, Mozambique, Palestine (Gaza Strip), and Peru (Courturier et al. 2012, Ward-Paige et al. 2013, Croll et al. 2016), where sometimes thousands of manta rays are landed per annum (Alava et al. 2002, Dewar 2002, White et al. 2006, Lewis et al. 2015). While many artisanal fisheries have grown to meet international trade demand for gill plates, some still target these rays mainly for food and local products (White et al. 2006, Essumang 2010, Rohner et al. 2017). 

Mobula rays, including Reef Manta Rays, are caught incidentally as bycatch throughout their ranges in at least 21 small-scale fisheries in 15 countries and 9 large-scale fisheries in 11 countries (Croll et al. 2016). Despite being unintentionally caught, mobulid rays are typically retained because of their high trade value. Even when discarded alive, e.g. from tuna purse seine fisheries, they are often injured and have high post-release mortality (Tremblay-Boyer and Brouwer 2016, Francis and Jones 2017). Many fisheries remain open and active even after dozens of national fishing bans and international listings on the appendices of both Convention for the Conservation of Migratory Species of Wild Animals (CMS) and the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) (Lawson et al. 2017, Lawson and Fordham 2018). 

Global landings of mobulid species, including Reef Manta Ray, have been increasing steadily due in large part to the recent rise (from the 1990s onwards) in demand for gill plates (Croll et al. 2015, O’Malley et al. 2017). Many former bycatch fisheries have become directed commercial export fisheries (Dewar 2002, White et al. 2006, Heinrichs et al. 2011, Fernando and Stevens 2011). Between 2000 and 2007, total landings of  'Mantas, devil rays, nei' ('nei' refers to 'not elsewhere included') increased from 900 tonnes to over 3,300 tonnes according to the FAO Fishstat Capture Production database (Lack and Sant 2009). While this equates to an average of 1,593 metric tonnes being landed per annum, reported landings are likely to represent only a fraction of total fishing-related mortality (Ward-Paige et al. 2013). 

In the markets of Guangzhou, China, where 99% of mobulid products are routed, mobulid products are sourced from over 20 countries and regions (O’Malley et al. 2017). The source locations for the largest amounts of product are Indonesia, Sri Lanka, India, China, and Viet Nam (O’Malley et al. 2017). Demand for products has driven up the price and traded volume of these products in recent decades. Between 2011 and 2013, there was an increase from 60 to 120 t of mobulid product moved through shops in Guangzhou (O’Malley et al. 2017). 

In the Western Indian Ocean, Romanov (2002) estimated that between 253 and 539 manta rays and devilrays were being caught per year as bycatch in purse seine fisheries, and between 2003 and 2007, 35 manta rays were observed in purse seine bycatch, some of which were likely Reef Manta Ray (Amande et al. 2012). In the Western and Central Pacific, from 2010–2015, observed bycatch of manta rays in purse seine fisheries was 4,176 individuals, and in longline fisheries was 226 individuals (based on distribution, some of these were likely Reef Manta Ray) (Tremblay-Boyer and Brouwer 2016). While a few individuals were released in good condition, post-release mortality is likely to be high as most were released alive but injured, or dead (Francis and Jones 2017). The Eastern Pacific purse seine fisheries show a substantial increase in the bycatch of mobulid rays, including Reef Manta Rays, from 20 tonnes per year before 2005 to 150 tonnes per year by 2006, which then reduced to 10 tonnes per year by 2009 (Hall and Roman 2013). The Inter-American Tropical Tuna Commission (IATTC) purse seine vessels operating during 2015 in the Pacific reported landings of 71 tonne of mobulid species, that likely included Reef Manta Ray (Miller and Klimovich 2017). 

While the overwhelming cause of population reduction is fishing mortality, sublethal effects and lower levels of mortality occur from numerous lesser threats, such as entanglement in nets, recreational foul hooking, and vessel strikes (Marshall and Bennett 2010b, Deakos et al. 2011, Couturier et al. 2012, Stewart et al. 2018). While there is no direct evidence, there are concerns for the effects of climate change, ocean acidification, oil spills, and other forms of pollution and contaminants (e.g. heavy metals) (Essumang 2010, Ooi et al. 2015, Stewart et al. 2018). Furthermore, shallow water lagoon nursery habitats are subject to habitat loss and degradation that pose threats to juvenile Reef Manta Rays (Stewart et al. 2018).

Mobulids are widely used for their meat, skin, liver oil, and gill plates (Couturier et al. 2012). The gill plates fetch high prices in Asia and are used for Chinese health tonics (O’Malley et al. 2017). The meat from mobulids is often used for food and shark bait or attractant, and the skin of mobulids is sometimes used for leather products (shoes, wallets, and knife handles).

The Reef Manta Ray is protected in over a dozen countries and territories (Lawson et al. 2017, Lawson and Fordham 2018). Local, national, and territory-level restrictions and/or protections for manta rays are currently in place in the USA (Hawaii), Australia and its territories, the Maldives, the United Arab Emirates, the Federated States of Micronesia (Yap), Thailand, Mozambique, Indonesia, and the Philippines. Even with legislative protection in some areas, fisheries for manta ray persist in others and there are more locations still where they are incidentally captured as bycatch in artisanal as well as small- and large-scale fisheries. With little to no effort to monitor or regulate mobulid fisheries in many countries, these current paper regulations are proving inadequate and misleading.

Manta rays have been listed in the appendices of a number of international conventions. The Reef Manta Ray was listed on Appendix I and II of the Bonn Convention for CMS in 2014, however, many CMS Parties have inadequate protections (Lawson and Fordham 2018). As a threatened species whose wide-ranging migratory tendencies put it at risk, this listing acknowledges the fact that this species would benefit from the implementation of cooperative international agreements to manage and protect its populations and encourages range states to work together toward this goal. Manta species (i.e. including Reef Manta Ray) were listed on Appendix II of CITES in 2013, requiring CITES Parties to legitimize all exports through a permitting system based on non-detriment findings which delimit acceptable, sustainable catches. 

Only a single Regional Fishing Management Organization (RFMO) has formally prohibited the retention of manta rays as bycatch, with most regulatory systems doing an inadequate job of protecting mobulid rays from fishing mortality. In 2015, recognizing the threatened status of mobulid rays, including the Reef Manta Ray, IATTC adopted recommendations which prohibited retaining, trans-shipping, landing, storing or selling, in whole or in part, any species of Mobula and required going forward that all mobulid rays be promptly released alive under strict non-detrimental protocols (Lawson et al. 2017, Lawson and Fordham 2018). Efforts should be put in place to reduce the unintentional capture of these rays and when they are caught, protocols should be in place for their safe release, to reduce the chances of post-release mortality.

Manta ray tourism in managed in some locations but if sustainable tourism industries are indeed to be developed around encounters with these rays, they should be legislated, continuously monitored, and enforced with permitting systems to make sure operators and tourists are adhering to best practice protocols and codes of conduct.