|Scientific Name:||Mobula thurstoni (Lloyd, 1908)|
Dicerobatis thurstoni Lloyd, 1908
Mobula lucasana Beebe & Tee-Van, 1938
|Taxonomic Source(s):||Last, P., White, W., de Carvalho, M., Séret, B., Stehmann, M. and Naylor, G. 2016. Rays of the World. CSIRO Publishing, Clayton.|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Walls, R.H.L., Pardo, S.A., Bigman, J.S., Clark, T.B., Smith, W.D. & Bizzarro, J.J.|
|Reviewer(s):||Francis, M.P., Marshall, A. & Couturier, L.I.E.|
|Contributor(s):||Sherman, C.S. & Lawson, J.|
|Facilitator/Compiler(s):||Walls, R.H.L. & Dulvy, N.K.|
The Bentfin Devil Ray (Mobula thurstoni) is a large ray (to 180 cm disc width), patchily distributed ray found in both the shallow, neritic waters (<100 m depth), and the offshore pelagic waters of tropical and subtropical seas worldwide. Devil rays are sensitive to even moderate levels of fishing pressure because they have extremely low reproductive rates (around one pup per year) and low post-release survival.
Increasing international trade in gill plates has led to the expansion of largely unregulated and unmonitored devil and manta ray fisheries worldwide. Trade pressure has likely increased for the gill plates of devil rays (including the Bentfin Devil Ray) as a result of declining availability of manta ray gill plates resulting from their recent CITES Appendix II listing. The Bentfin Devil Ray is taken as bycatch in gillnet, purse seine, and longline fisheries in the Pacific, Indian, and Atlantic Oceans, and is targeted in Peru, the Philippines, Mexico, India, Myanmar, Sri Lanka, and Indonesia for both meat consumed domestically and gill plates for international trade. The lack of species-specific catch, fishing effort, and population data necessitates the use of genus-wide inferences on population reduction particularly from the Bentfin Devil Ray’s congener, the Chilean Devil Ray (M. tarapacana). Where documented, catches are decreasing yet known fishing effort is stable or increasing, suggesting that populations are declining. For the purpose of this assessment (and similar to the Chilean Devil Ray), the Bentfin Devil Ray’s range was been divided into seven regions: Indo-West Pacific, central Pacific, eastern Pacific, western Atlantic, eastern Atlantic, Indian Ocean, and Australia. In the last decade, population reductions have been either inferred or suspected in four of seven regions examined: Southeast Asia, Eastern Pacific, Indian Ocean (particularly in Indonesia and Sri Lanka, where they are heavily fished), and Australia. In three of these regions, the Bentfin Devil Ray is strongly suspected to be Vulnerable based on genus-wide population reductions (equivalent to >30% over a three-generation span). In Australia, there are no target fisheries but this species is suspected to be Near Threatened due to the occurrence of bycatch in domestic shark fisheries, in the Shark Control Program, and in unmonitored illegal fisheries from other countries. In the remaining three regions (the central Pacific, western Atlantic, and eastern Atlantic), the Bentfin Devil Ray is Data Deficient.
The relationship between these regional declines and the global population trend is not directly known and there is considerable uncertainty surrounding these trend data. Wide-ranging movements and migration, however, probably connect these regions and hence steep local declines are likely to influence global population sizes. The Bentfin Devil Ray is suspected to have declined by almost 30% over three generations throughout its global range, which combined with international trade value and demand for devil ray gill plates, domestic demand for meat, high intrinsic sensitivity to overexploitation, and the likelihood that fishing effort will increase, leads to this species being assessed as Near Threatened. The collection of species-specific population, catch, distribution, and trade data is highly recommended to allow for a more comprehensive assessment of this highly sensitive species in future.
|Previously published Red List assessments:|
With a circumglobal distribution, the Bentfin Devil Ray is found in tropical, subtropical, and temperate waters of the Pacific, Atlantic, and Indian Oceans (Couturier et al. 2012). This species probably occurs in many other locations from which it has not yet been identified. It was documented in Australian waters from a few sightings off Mackay and Port Douglas (Queensland) and at Ningaloo Reef (Western Australia) from where it was previously unconfirmed (Last and Stevens 2009).
Native:Australia; Brazil; Chile; Costa Rica; Côte d'Ivoire; Ecuador; Egypt; El Salvador; Guatemala; Honduras; India; Indonesia; Japan; Malaysia; Maldives; Mexico; Myanmar; Nicaragua; Oman; Pakistan; Peru; Philippines; Saudi Arabia; Senegal; South Africa; Sri Lanka; Thailand; United Arab Emirates; United States (California); Uruguay; Vanuatu
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – southwest; Atlantic – southeast; Atlantic – eastern central; Indian Ocean – eastern; Indian Ocean – western; Pacific – southeast; Pacific – northwest; Pacific – eastern central; Pacific – western central; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||There are no historical baseline population data and global population numbers are unknown for any devil ray species. However, regional, genus-wide declines are inferred based on catch landings, trawl-survey indices, and diver sightings (Couturier et al. 2012, Ward-Paige et al. 2013, White et al. 2015, Croll et al. 2015, Lewis et al. 2015). The scale and effects of devil ray fisheries in Sri Lanka, India, Indonesia, the Philippines, and Peru suggest considerable population reduction (Heinrichs et al. 2011, Lewis et al. 2015).|
Devil rays have population sizes likely one or two orders of magnitude greater than manta rays, have larger geographic ranges, and larger migratory movements. This makes devil rays more challenging to assess than manta rays. By comparison, manta rays can be easily locally depleted because they appear to be restricted geographically, and hence declines are likely to be genus-wide. The Bentfin Devil Ray is less frequently encountered in catches compared to other species of devil ray, which makes this species particularly difficult to assess compared to devil rays that are more frequently encountered (e.g., the Chilean Devil Ray). Given the paucity of data across the entire Mobula genus, most population trend data for devil rays are not species-specific. Hence, most of the decline rates in this assessment were necessarily inferred from these genus-wide declines. Local population trend data are available from market landings, a trawl survey index, and diver surveys.
Given the patchy nature of the Bentfin Devil Ray’s occurrence, its range has been divided into seven regions for the purpose of this assessment: Indo-West Pacific, central Pacific, eastern Pacific, western Atlantic, eastern Atlantic, Indian Ocean, and Australia. Next, the status of this species in each of these regions was considered, before drawing these together into a global estimate of population reduction.
In Indonesia, catches of the Bentfin Devil Ray were recorded in the country’s three largest devil ray landing sites (Tanjung Luar, Lombok; Lamakera, Solor; Cilacap, West Java). Landed mobulid (devil and manta ray) catch was estimated to have declined by 77–99% over the past 10–15 years in these three landing sites and there was evidence of increased directed fishing effort at two sites (Tanjung Luar and Lamakera; Lewis et al. 2015). Local population depletions can be inferred from an increase in the number of operating fishing vessels concurrent with these landed catch declines. The number of vessels catching devil rays from Tanjung Luar has increased since 2014 but any longer-term trend is unquantifiable owing to a lack of effort data. From Lamakera however, the number of vessels fishing devil rays has approximately doubled since 2001 (S. Lewis, unpublished data). Although this species is suspected to be naturally rare compared to its congener the Chilean Devil Ray (Compagno 1999) based on catch proportions, in Tanjung Luar it was the most commonly caught devil ray species from 2013–14, making up 49% of total catch (Lewis et al. 2015).
There appears to have been a recent expansion and collapse of devil ray fisheries due population depletion in Bohol, Philippines. Historically, from the 1900s to 1960s the devil ray fishing grounds were inshore (within five km of shore), but subsequently expanded to offshore waters extending over the jurisdiction of municipal waters (15 km from the coastline) following fleet modernization in the 1970s. By 2014, the devil ray fishing grounds had contracted to a smaller area in the northeast of the Bohol Sea, suggesting a decrease in devil ray fishing effort led by several factors including a possible depletion of fishing grounds and decrease in financial viability of the fishery, compared to historical records (J. Acebes and A. Ponzo, unpublished data).
Interviews with fishermen in the Philippines indicate villages take as many as 1,000 devil rays per year, and the number of villages and fishermen participating in the fishery expanded through 2002. This is concurrent with declines in catch rates, therefore local population declines can be inferred but not quantified (Alava et al. 2002).
Population reductions can be suspected or inferred from three forms of data: (i) diver sightings from Cocos Island, (ii) bycatch rates in tuna purse seine fleet, and (iii) fisheries landings in Peru.
Over the past 21 years there has been a 78% decline in devil ray sighting probability at Cocos Island, Costa Rica reported from diver surveys (White et al. 2015). Over this time period, devil rays were generally rare and seen on only 7% of dives. While species-level identifications were not available in this study, area dive operators report the Chilean Devil Ray as the species generally sighted (E. Herreno, pers. comm. 2012), so it is unclear whether the Bentfin Devil Ray occurs in lower numbers or not at all. The degree to which this index reflects wider population reduction remains to be fully understood, however, the Cocos Island is one of the world’s oldest Marine Protected Areas, and lies within the area of activity of the Eastern Tropical Pacific tuna purse seine fisheries, which take large numbers of devil rays as incidental catch (Croll et al. 2015, White et al. 2015). Fishing effort and species-specific data from this region are currently unavailable for quantification of declines.
The Inter-American Tropical Tuna Commission (IATTC) catch and bycatch data for devil rays from purse seine fisheries in the eastern Pacific between 1998 and 2009 show a significant increase from <1t in 1998 to >80t in 2006, and a subsequent decline over three years until 2009, where the reported catch was 40t (Hall and Roman 2013). While population trends cannot be directly taken from grouped species bycatch data such as these, this pattern may be indicative of overall devil ray population declines following overexploitation in the region, depending on the corresponding trajectory of fishing effort.
Already in the early 1980s concern existed over the sustainability of Bentfin Devil Ray catch in the Gulf of California (Mexico). Growth overfishing may have been occurring as 72% of individuals caught were immature (Notarbartolo di Sciara 1988). Since this study in the 1980s, however, no data have been published on the Bentfin Devil Ray in these waters, so it is impossible to determine catch trends over time.
In Tumbes, Peru, while reported devil ray landings fluctuate considerably from year to year there is a significant decline from an apparent peak of 1,188t in 1999 (Llanos et al. 2010), to 135t in 2013 (IMARPE 2014), although reported devil ray landings fluctuate considerably from year to year. Llanos et al. (2010) describe all the devil rays landed as the Bentfin Devil Ray, but these statistics probably also include the Chilean Devil Ray. This is likely, as a more recent fishery survey found mobulid landings in Tumbes between 2013 and 2014 to consist mainly of the Spinetail Devil Ray (M. japanica, 93% of individuals), followed by the Smoothtail Devil Ray (M. munkiana, 5%). The Bentfin and Chilean Devil Ray were also caught, but each species only accounted for 1% of the total number of devil rays landed (SOSF 2014). The short duration of this survey, however, means that these data cannot be used to determine species-specific catch or effort trends over time. Fishing effort is unknown, but given that international demand is likely to continue and possibly increase, this decline in landings may be indicative of overall devil ray population declines in the region.
In Sri Lanka, population reductions are suspected because fishermen reported declines in devil ray catches over the past five-to-ten years as targeted fishing pressure has increased, and it is estimated that the Bentfin Devil Ray contributes to 1% of the total catch of devil rays (Fernando and Stevens 2011, Heinrich et al. 2011). This suggests local population decline, but the decline cannot be quantified at present due to a lack of catch, landings, or effort data to support this statement (e.g., Sri Lanka National Plan of Action for Sharks 2013). Traditionally, mobulids were not fished in Sri Lanka due to the poor quality of their meat, but recently the demand for gill plate export has fuelled targeted fisheries with >55,000 mobulids taken annually in gillnet fisheries, representing >50% of global targeted mobulid catches (Fernando and Stevens 2011, Heinrichs et al. 2011).
In India, population reductions are suspected based on declining devil ray catches and increased effort in several regions, including Kerala, Chennai, Tuticorin, and Mumbai (Mohanraj et al. 2009, Couturier et al. 2012). Catch per unit effort (CPUE) analyses from trawlers in Mumbai waters revealed maximum landings of 6.3 tonnes (t) for “M. diabolus” (an invalid name, possibly referring to the Bentfin Devil Ray and several other devil ray species) in 1993–1995 surveys, declining to 4.8t in 1996–98, and then to 3.1t in 1999–2001 and 2002–2004 (Raje and Zacharia 2009). This represents a 51% decline in landings over approximately 10 years during which fishing effort almost doubled, and local population declines can be inferred. Such declines are unquantifiable to species level given the potential grouping of several species under one synonym. We caution that trawling indices may not provide accurate trend estimates for mid-water species such as devil rays, and that the reported catches were very small, but the change in index is consistent with a decline in some combination of abundance, spatial extent, or catchability, which are indicators of population reduction. Additionally, it cannot be confirmed whether the Bentfin Devil Ray has been captured under the “M. diabolus” label at all, although the range overlap and species composition of other catch data from this region suggest it is likely.
Population reduction and three-generation decline rates
The six ocean regions that were used to assess the status of the Chilean Devil Ray are listed below as a reference. The likely threat categories are only tentative rather than actual regional assessments:
The seven ocean regions used as a reference to assess the status of the Bentfin Devil Ray are listed below. Compared to the Chilean Devil Ray, Australia was separated out in this Bentfin Devil Ray assessment. The likely threat categories and the type of decline data available are laid out for transparency and to enable aggregation to a global assessment, rather than representing actual regional or subpopulation assessments:
The available information suggests population reductions are occurring in multiple regions, however these data are highly uncertain and many of these trends are suspected from genus-wide measurements rather than species-specific data. In addition, we have no data from certain regions where this species is also being heavily fished. While wide-ranging movements and migration possibly connect these regions (Thorrold et al. 2014) and steep local declines may reflect a global population reduction, we cannot extrapolate the magnitude of suspected regional declines (~50% over three generations) to the global population. Nonetheless, it is suspected that the Bentfin Devil Ray has declined globally at rates nearing 30% over a three generation span at the very least, thus warranting a Near Threatened status. Furthermore, the causes of these declines are likely to be maintained as demand for gill plates will continue, thus future declines at similar rates can be suspected.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The Bentfin Devil Ray is usually pelagic or epipelagic in shallow, productive, neritic waters of <100 m depth (Notarbartolo di Sciara 1988, Croll et al. 2015), although it is also caught in offshore pelagic waters (Mas et al. 2015), and around seamounts in the Mid-Atlantic Ridge (Mendonça et al. 2012). Segregation by size and sex is seasonal, with all size classes and sexes appearing together during the summer months (Notarbartolo di Sciara 1988). The species is observed either solitarily or in small groups (2–6 individuals); it is not a schooling species (Notarbartolo di Sciara 1988). The southern Gulf of California is apparently an important feeding and mating ground, and southwest Brazil appears to be an important mating ground (Casas et al. 2006). The Bentfin Devil Ray is predominantly planktivorous (Gadig et al. 2003), but this does not rule out the possibility that it might also be piscivorous, which would increase its susceptibility to capture by longline.|
Both females and males from the Gulf of California, Mexico are estimated to mature at 150 cm disc width (DW), while size at birth is estimated at 65–85 cm DW (Notarbartolo di Sciara 1988), and maximum size on record is a 183 cm DW female from 50–80 m depth off Brazil (Casas et al. 2006). DW at 50% maturity was estimated at 153.8 cm for males (White et al. 2006b). The mode of reproduction is matrotrophic viviparity. Embryos obtain nutrients initially via yolk, then through absorption of enriched uterine fluid from the mother (Wourms 1977). Only the left ovary is functional and litter size is one pup after a 12-month gestation period (Wourms 1977, Notarbartolo di Sciara 1988). It is estimated that the maximum intrinsic population growth rate (rmax) of devil rays is similar to manta rays, and these productivity rates are among the lowest of all chondrichthyans (Dulvy et al. 2014, Pardo et al. 2016). Mating, parturition, and early life history are reported to take place in the shallow water during summer and perhaps early autumn (Notarbartolo di Sciara 1988), although a pregnant Bentfin Devil Ray was encountered near two seamounts on the Mid-Atlantic Ridge (Mendonça et al. 2012)
For the Spinetail Devil Ray (up to 310 cm DW), Cuevas-Zimbrón (2012) estimated age at maturity to be 5–6 years and a minimum lifespan of 14 years, giving a generation length of 10 years. While accurate age at maturity and longevity information is unavailable for the Bentfin Devil Ray, it can be inferred according to the smaller maximum size that it would be close to but slightly shorter than that of its congener. As there are not enough data to estimate an exact generation length for this species, an approximate, suspected generation length is used. A midway point of 7.5 years between a very conservative low of five years, and the larger Spinetail Devil Ray’s 10-year generation length is suspected to be the approximate generation length for the Bentfin Devil Ray until more accurate information becomes available.
|Generation Length (years):||7.5|
|Use and Trade:||
The dried branchial filter plates (gill plates or pre-branchial appendages) from devil rays are used in an Asian health tonic purported to treat a wide variety of conditions (Heinrichs et al. 2011, Couturier et al. 2012). Recent surveys suggest an escalation in demand for devil ray gill plates in China, with the estimated number of devil rays represented in Guangzhou, China gill plate markets more than doubling from early 2011 to late 2013 (O’Malley et al. in press). The Bentfin Devil Ray was identified as one of the most prevalent devil ray species in the Guangzhou gill plate markets, however because of the similarity to other species’ gill plates such as the Spinetail Devil Ray, it was not possible to determine the proportion of Bentfin Devil Ray gill plates in stock estimates; grouped Spinetail Devil Ray and other devil ray gill plates including the Bentfin Devil Ray made up 30% of market stocks in 2011 (O’Malley et al. in press). This category of gill plates is reported to sell for up to US$290 per kg (O’Malley et al. in press). Gill plates are traded to China from Indonesia (Dewar 2002, Lewis et al. 2015), the Philippines (Alava et al. 2002, Acebes 2013), Sri Lanka (Fernando and Stevens 2011), India (Fernando 2012), Vietnam, Thailand, Myanmar, Japan, Africa, South America, and the Middle East (O’Malley et al. in press). While no specific data are available to quantify declines, 64% of sellers of devil ray gill plates at Guanzhou market, China claimed that supply of the product had decreased in 2014, with two interviewees claiming the market for this product “has no future” (O’Malley et al. in press). This could be reflective of the inability of such slow growing species to maintain population size in the face of current exploitations levels, depending on the trajectory of fishing effort involved; in the case of increasing fishing effort this would further indicate regional population decline.
The relatively low-value meat is most often used locally for human consumption, shark bait, fishmeal, or animal feed (Couturier et al. 2012, Croll et al. 2015). Fishers in Senegal have reported exporting dried devil ray meat for human consumption to neighbouring African countries such as Ghana, Togo, and Mali (Ender and Fernando 2014). In Guinea, devil ray meat is exported as smoke-dried meat to the Ivory Coast, Sierra Leone, and Liberia, and as salt-dried meat to Nigeria, Ghana, and Togo (F. Doumbouya, pers. comm. 2015). Devil rays are also used for cartilage, which is exported as filler for shark fin soup; for skin, which is exported for leather production (Croll et al. 2015); and to make chondroitin sulfate supplements for export to Japan and Britain (Heinrichs et al. 2011).
Threats to the Bentfin Devil Ray include targeted and incidental catch in both artisanal and large-scale fisheries. Directed fisheries and retention in bycatch fisheries are increasingly driven by the international trade demand for gill plates (Rajapackiam et al. 2007, Heinrichs et al. 2011, Couturier et al. 2012, Kizhakudan et al. 2015). This species’ epipelagic tropical distribution in regions of high productivity, which overlaps with that of tuna and other highly valued target teleost (bony fish) species, means it is exposed to multiple targeted and bycatch fisheries (White et al. 2006b, Couturier et al. 2012, Croll et al. 2012, Croll et al. 2015). Collectively, it is estimated that over 94,000 devil rays are landed worldwide (Heinrichs et al. 2011). Within the global purse seine fishery around 13,000 individual mobulids are captured each year (Croll et al. 2015).
Large declines in devil ray landings have been recorded in fisheries supplying the gill plate trade over the past 10–15 years since this trade began to expand (Lewis et al. 2015). Although devil ray meat is generally not highly valued (Couturier et al. 2012), artisanal fisheries also target devil rays for food and local products using a variety of methods including harpooning, longlining, handline, netting, and trawling (White et al. 2006a, Ayala 2008, Fernando and Stevens 2011, Heinrichs et al. 2011, Acebes 2013). Reports from fishermen and traders of devil ray gill plates indicate that devil ray gills are becoming harder to source, with prices escalating as the supply continues to decline (O’Malley et al. in press).
There are 13 fisheries (mostly artisanal) in 12 countries that specifically target devil rays, and 30 fisheries in 23 countries that incidentally catch devil rays (Croll et al. 2015). Devil rays are reported as bycatch in nine large-scale fisheries in 11 countries using driftnets, trawls, and purse seines, and in 21 small-scale fisheries in 15 countries using driftnets, gillnets, traps, trawls, and longlines (Croll et al. 2015). Between 1998 and 2009, global landings of devil rays increased by more than an order of magnitude, from 200–5,000 t (Ward-Paige et al. 2013).
The global tuna purse seine fishery is a particularly important source of devil ray bycatch, with devil rays reported in five tuna fisheries from eight countries (Croll et al. 2015). Furthermore, devil rays are usually not identified to species level in bycatch reports (Hall and Roman 2013). The Giant Manta Ray (Manta birostris), the Reef Manta Ray (M. alfredi), the Smoothtail Devil Ray, the Spinetail Devil Ray, the Chilean Devil Ray, and the Bentfin Devil Ray have been reported as bycatch in purse seines (Hall and Roman 2013). The frequency of devil ray captures and number of individuals caught per net set is generally relatively small (averaging <0.45 individuals per set, see below), but global distribution of purse seine fisheries and the large number of sets presents concern for mobulid conservation as approximately 13,000 individuals are captured each year (Croll et al. 2015).
While previously mainly taken in Indonesia as bycatch of the inshore pelagic tuna gillnet fisheries and purse seine fisheries, devil rays are increasingly being targeted in response to Asian demand for devil ray gill plates (Dewar 2002, White et al. 2006b, Heinrichs et al. 2011, Couturier et al. 2012, Lewis et al. 2015). Gillnet fisheries target large numbers of devil rays in Indonesia, the Philippines, Mexico, India, the eastern and western coasts of Africa (Couturier et al. 2012), and Sri Lanka (Fernando and Stevens 2011).
Targeted mobulid harpoon fisheries have been documented across Indonesia including Lombok, Lamakera, Lamalera, and villages in the Alor region (Dewar 2002, White et al. 2006a, Croll et al. 2015). In Tanjung Luar (Lombok), a number of fishers reported a shift in focus to devil rays as a primary target since 2010 (Lewis et al. 2015). In the traditional whaling villages of Lamakera (Indonesia), the primary focus of fisheries has shifted from whales to manta and devil rays, the dominant devil ray species caught is the Chilean Devil Ray, with the Bentfin Devil Ray the third most commonly caught devil ray (Dewar 2002, Lewis et al. 2015). These fisheries have increased effort in terms of power and number of boats in recent years, resulting in an increase in local fishing pressure equivalent to an order of magnitude (Dewar 2002, Lewis et al. 2015).
In Bohol, the Philippines, devil ray fishing grounds expanded significantly from small coastal waters within five km of shore from the 1900s to 1960s, to offshore waters extending over the jurisdiction of municipal waters (15 km from the coastline) following fleet modernization (or motorization) in the 1970s. By 2013–14, the devil ray fishing grounds from Bohol had contracted to a smaller area in the northeast of the Bohol Sea, suggesting a decrease in devil ray fishing effort led by several factors including a possible depletion of fishing grounds and decrease in financial viability of the fishery, compared to historical records (Acebes 2013, A. Ponzo, unpublished data, 2014).
A targeted harpoon fishery existed for devil rays in Taiwan from 1930–60, with contradictory reports about its continued existence (Chen et al. 2002, Camhi et al. 2009), although it is unclear as to whether the Bentfin Devil Ray was affected by this fishery as the main target was the Spinetail Devil Ray.
Despite national protection in Mexico, illegal targeted catch and substantial mortality of devil rays from artisanal and large-scale fisheries still occurs (Croll et al. 2012). In ports around Tumbes, Peru, around 45% of fishing trips in which devil rays were caught were actively targeting the genus (SOSF 2014).
There are artisanal fisheries in multiple West African countries that target devil rays for human consumption both locally and for exporting to other markets (Couturier et al. 2012, Ender and Fernando 2014). However, little is known about the extent of these fisheries at present, and it is still uncertain whether the Bentfin Devil Ray inhabits these waters.
Targeted fisheries are reported in Sri Lanka (Fernando and Stevens 2011), India (Rajapackiam et al. 2007), and Myanmar (A. Tilley, pers. comm. 2015). In Sri Lanka, traditionally, mobulids were not fished due to the poor quality of their meat, but recently, demand for gill plate export has fuelled targeted take, with an estimated 450 Bentfin Devil Rays landed annually (Fernando and Stevens 2011, Heinrichs et al. 2011).
In India, targeted devil ray ﬁsheries are reported along the coast of Chennai, Tuticorin, Mumbai, and Veraval, within the Union Territory of Lakshadweep, and in the Andhra Pradesh and Kerala regions (Couturier et al. 2012). Following the high demand for devil ray products, a new ﬁshery formed along the Chennai coast using mechanized gillnets (Rajapackiam et al. 2007). The Bentfin Devil Ray is fished on the west and east coast of India in marine, pelagic-oceanic, and benthopelagic/reef associated environments, primarily through use of gillnets and is commonly caught in the fishery (Kizhakudan et al. 2015). In recent years, trade in devil and manta ray gill plates has increased in Chennai (Kizhakudan et al. 2015), and this trade appears to be linked to a sudden increase in devil ray landings (Nair et al. 2013), although the increase in landings cannot be linked directly to the Bentfin Devil Ray at present. There is also a seasonal harpoon fishery for devil rays in Andhra Pradesh, northeast India, and in Lakshadweep, north of the Maldives (Pillai 1998). No catch or effort data are available from this fishery at present to determine the extent to which it might affect the Bentfin Devil Ray.
There are no known targeted fisheries for any devil rays in this region.
The Bentfin Devil Ray is taken as bycatch (retained or discarded) in industrial and artisanal fisheries targeting other species throughout the Atlantic, Pacific, and Indian Oceans, most frequently in purse seines and gillnets (Couturier et al. 2012, Croll et al. 2015) but also in longlines. Gillnet fisheries take large numbers of devil rays, including the Bentfin Devil Ray, as incidental catch in Indonesia, the Philippines, India, Sri Lanka, and possibly Mexico and the eastern and western coasts of Africa (Couturier et al. 2012). The Bentfin Devil Ray is also captured incidentally in Uruguay, Brazil (Mas et al. 2015), Peru (SOSF 2014), Costa Rica (Dapp et al. 2013), and Malaysia (A. Hochstetter, pers. comm. 2012).
Croll et al. (2015) estimated global mobulid bycatch in purse seine fisheries to be ~13,000 devil rays per year. There is evidence for moderate to high post-release mortality of the Spinetail Devil Ray after incidental capture in purse seines (Francis and Jones 2016). In the purse-seine fishery, individuals undergo a process of encirclement, sacking up, and brailing on board; while many rays are alive when released, the release methods used in many cases are harmful (Croll et al. 2015, Mas et al. 2015), suggesting that even low levels of incidental capture can have a considerable negative effect on populations. Coelho et al. (2011, 2012) found very low at-haulback mortality of devil and manta rays from pelagic longline fisheries in the Atlantic and Indian Oceans, although these studies only considered the short-term mortality from actual capture and did not monitor post-release survival. Given the results from Francis and Jones (2016), it is possible that internal trauma and stress resulted in slightly delayed mortality of these individuals, therefore these studies should not be used as an indicator of post-release mortality for these sensitive species.
Devil rays are caught as bycatch (and retained) in drift gillnet Skipjack Tuna (Katsuwonus pelamis) fisheries in Indonesia, where the Bentfin Devil Ray accounts for 8.8% of all mobulids caught (White et al. 2006b). An estimated 362 Bentfin Devil Rays are landed annually in four landing sites in Indonesia (White et al. 2006b). No effort data are currently available from this region.
Devil rays (labelled as manta rays) were noted as one of the common elasmobranch species identified by observers in purse seine fisheries in the Pacific Island countries and territories (Lack and Meere 2009). In the western and central Pacific tuna purse seine fisheries, mobulids were found in 7.4% of sets observed between 1994 and 2004 (Molony 2005).
In the eastern Pacific tuna purse-seine fishery, devil rays are most commonly taken in school sets and dolphin sets (Hall and Roman 2013). Average devil ray capture rate (individuals per set) was 0.38 per set for school sets, 0.08 per set for dolphin sets, and 0.02 per set for floating object sets (Croll et al. 2015). Although the fishery operates across the Eastern Central Pacific, devil ray captures were concentrated in regions of high productivity and prey density (particularly euphausiids; Croll et al. 2015).
The estimates of mortality for the eastern Pacific for the period 1993–2013 average almost 2,800 individuals per year, with a range of 1,100–6,500 (Croll et al. 2015). Much of the devil ray take in this fishery occurs in the Costa Rica Dome region off Central America (Croll et al. 2015), but is also occurring south to the coast of Peru (SOSF 2014). In Northern Peru, mobulids were caught as bycatch in 55% of fishing trips that reported them (SOSF 2014), and 55% of artisanal gillnet fishermen reported devil ray bycatch (Ayala 2008).
Devil rays are taken as bycatch in pelagic gillnet and longline fisheries in the Indian Ocean targeting swordfish (Coelho et al. 2011), and the tuna purse seine fishery (Lezama-Ochoa et al. 2015). Effort trends for these fisheries are unknown. Most chondrichthyan catch in this fishery is discarded, although post-release survival rates are not available. Devil rays are also caught in relatively low numbers in the bather protection nets of the Kwazulu-Natal Shark Control Programme; from 1981-1990, the average annual catch was 14.2 devil rays per year, with an average of 60% released (Dudley and Cliff 1993). A later study by Young (2001) reported that the KwaZulu-Natal shark-control nets caught 1,191 manta rays (Manta spp.) and 440 devil rays (Mobula spp.) between 1981 and 2000, with up to three individuals caught per day. Mobulids constituted 12% of the total catch by number from these nets between 1981 and 1990, with a mean annual catch of 66 individuals and an average mortality rate of 33%.
Devil rays are taken as bycatch in pelagic longline fisheries in the South West Atlantic Ocean Uruguayan and Japanese Longline Fisheries (ULF and JLF, respectively), which operate within the Uruguayan Exclusive Economic Zone (EEZ; ULF and JLF) and adjacent international waters (ULF; Mas et al. 2015). Mas et al. (2015) estimated trends in devil ray bycatch in these fisheries from 1998–2012 for the ULF and 2009–2011 for the JLF, and found that only 201 devil rays were incidentally caught during that time, equaling a catch-per-unit-effort (CPUE) of 0.028 individuals per 1,000 hooks, which represents only 0.5% of both fleets’ total catch combined. Catches of devil rays fluctuated over the study period, with a peak in 2006 of just under ~20 individuals caught, decreasing again until a peak in 2009 of <50 individuals caught, remaining high until catches fell again to <10 in 2012 and less than five in 2013 (Mas et al. 2015). The devil rays identified in these fisheries included the the Spinetail Devil Ray and the Bentfin Devil Ray, but as only 38% of the fisheries are covered by observers, only 14% of devil ray bycatch was identified to species level based only on photo or video identification. Depending on corresponding fishing effort, which is currently unavailable, this may indicate regional population declines.
Eastern Atlantic: Industrial trawlers operating off the northwest African coast also capture devil rays, with up to 620 individuals caught per year, most likely including the Bentfin Devil Ray (Zeeberg et al. 2006, Couturier et al. 2012).
Devil rays are caught as bycatch in gillnets of the Queensland East Coast Inshore Finfish Fishery (Harry et al. 2011) and in nets used in the Queensland Shark Control Program (Sumpton et al. 2011), although catch levels are unknown for either.
In the context of carrying out species-specific population trend analyses, the misidentification of devil ray species in catches and landings poses a threat to the entire genus by confounding accurate determination of each species’ population status. Devil ray bycatch data, if recorded at all, has historically been recorded under various broad categories such as “Other”, “Rays”, or “Batoids”, but almost never recorded to species level (Camhi et al. 2009, Lack and Sant 2009). As such, the Bentfin Devil Ray has generally been overlooked in most oceanic fisheries reports, with very little effort to properly identify or accurately record the species caught (Camhi et al. 2009, Croll et al. 2015). It is possible that the larger devil ray species such as the Bentfin Devil Ray are declining more rapidly than the smaller species (Dulvy and Reynolds 2002), but this is currently impossible to determine. A lack of appropriate species-specific catch, effort, and population information poses a barrier to the conservation and management of devil rays.
The Giant and Reef Manta Rays were listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora in 2013, yet no devil ray species have been listed. Following these protective measures for mantas there are concerns that the ongoing demand for gill plates will shift to focus on the devil rays.
Genetic research into devil ray evolution suggests that periods of global warming may have led to regional extinctions in the past (Poortvliet et al. 2015), thus current increases in global temperatures (van Nes et al. 2015) could also pose a growing threat.
All species of devil ray were added to Appendix I and II of the Convention on Conservation of Migratory Species (CMS CoP11), designating them as migratory species at high risk of extinction that would benefit from strict prohibition of take and regional cooperation to protect their critical habitats and migratory paths. In February 2016, all species of devil ray including the Bentfin Devil Ray, were added to Annex I of the CMS Memorandum of Understanding on the Conservation of Migratory Sharks (CMS Sharks MOU). This non-binding agreement among 40 Signatories (as of June 2016) aims to achieve and maintain a favourable conservation status for migratory sharks based on the best available scientific information while taking into account the socio-economic value of these species. To date Australia (2015), the European Union (2015), the Maldives (Environment Protection Agency rule, 2014), Brazil (Inter-ministerial Normative Instruction No. 2 of 14/3/2013), Ecuador (Ecuador Official Policy 093, 2010), Mexico (NOM-029-PESC-2006, 2007), and Israel (2005) have passed national legislation to protect the Bentfin Devil Ray through fishing and/or trade restrictions (Lawson et al. 2016). This species is also protected in three states or provinces in the United States (Florida, Guam, Commonwealth of the Mariana Islands), the Raja Ampat Regency (Indonesia) and Christmas and Cocos Keeling Islands (Australian Indian Ocean Territories).
Devil ray landings are rarely recorded to species level. Improved clarity in catch records and required, standardized reporting of devil ray catch by the Regional Fishery Management Organizations (RFMOs) would provide a basis for monitoring trends in effort and landings. Similarly, reporting of corresponding fishing effort trends is requisite for calculation of population trajectories. In 2015 the Inter-American Tropical Tuna Commission (IATTC) passed a prohibition on the transshipment, storage, landing, and sale of all devil and manta rays taken in large-scale fisheries within the IATTC convention area. The measure includes requirements for reporting devil ray catch data and ensuring safe releases, as well as provisions for technical assistance and capacity building. Developing countries were granted exceptions for devil and manta rays taken in small-scale fisheries for domestic consumption (IATTC 2015). Elasmobranch fisheries are generally unmanaged throughout Central America and Southeast Asia, and indeed elsewhere in the range of this species, and attempts to regulate fisheries in these regions would greatly improve conservation of the Bentfin Devil Ray and other devil rays.
The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species across the regions where this ray occurs. There is a lack of progress on successfully implementing shark National POAs (Davidson et al. 2015), especially with regards to devil rays.
The sensitivity of the Bentfin Devil Ray, along with evidence of substantial CPUE where this species is fished, continued strong international demand for devil ray gill plates, and unmanaged, unmonitored fisheries throughout much of its range, calls for international conservation measures. These will need to focus on management of fisheries and trade, and reduction of demand for devil ray products.
The combination of i) unmanaged, unmonitored target and bycatch fisheries throughout the Chilean Devil Ray’s range; ii) evidence of substantial devil ray catch in several of these fisheries; iii) continued strong international demand for devil ray gill plates; and iv) the inherent sensitivity of the species, necessitates international conservation measures. These measures would ideally focus on management of fisheries and trade, and reduction of demand for devil ray products.
|Errata reason:||Correction made to the second author name for this assessment, from "Pardo, S.P." to "Pardo, S.A."|
|Citation:||Walls, R.H.L., Pardo, S.A., Bigman, J.S., Clark, T.B., Smith, W.D. & Bizzarro, J.J. 2016. Mobula thurstoni (errata version published in 2016). The IUCN Red List of Threatened Species 2016: e.T60200A100016879.Downloaded on 24 September 2018.|
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