Tags: Economics,  Gill Raker,  Ray Threats 

Ray Fisheries

Sri Lanka

Through May to September 2011 the Manta Trust conducted surveys at the Negombo and Mirissa fish markets to evaluate the extent of the manta and mobula ray fishery in Sri Lanka. Total landings were estimated at 1,055 manta rays (M. birostris) and 55,497 mobula rays (various species) per year, making Sri Lanka responsible for over 55% of known global manta and mobula ray catches.

The overwhelming majority (at least 87%) of the M. birostris recorded were juveniles and sub-adults, indicating a potential manta ray ‘nursery’ ground close to shore in southern Sri Lanka that is being heavily targeted. It is extremely rare to observe juvenile M. birostris in the wild, and if this area is indeed an important aggregation site for juvenile M. birostris, it would be the first of its kind reported anywhere in the world.

Fishermen report that catches have decreased over the past three to five years, coinciding with the increase in the gill raker trade over this period. In line with Indonesian investigations, it’s clear that the demand for gill rakers is driving this fishery where per kilo prices for gill rakers are as much as 250 times the price of meat, meat that is frequently sold as animal feed (mainly chicken and shrimp farms).

Historically in Sri Lanka, mobulid rays were caught primarily as by-catch or were avoided altogether by the fishermen, due to their propensity to destroy or entangle fishing nets and because their meat is hard to keep fresh for long periods at sea. While the middlemen in the mobulid supply chain still take the bulk of local profits, recent massive increases in gill raker demand, and dwindling supplies of other more desirable catches (such as sharks, tuna and billfish), now give fishermen ample incentive to actively target mobulids.

India

 India has the second largest elasmobranch fishery in the world, with reported landings of 70,000t per year, representing ~ 10% of the global elasmobranch catch1. While the full extent of mobulid landings in India is not known, numerous published references document significant manta and mobula ray landings from the Indian coastal trawl, gillnet and longline fisheries. The available fishery reports account for at least 690 manta rays (M. birostris) and an estimated 24,260 mobula rays (various species).

Given the vast size of the Indian trawl and gillnet fleets targeting sharks, skates and rays, and limited fisheries oversight, the landings of mobulids in these fisheries may be significantly underreported. Likewise, with well-organized harpoon fisheries for M. birostris reported on both east and west coasts of India with no landings data available, there is again the strong possibility of significant landings not accounted for in the fisheries data. To properly estimate total manta and mobula ray landings in India, further investigation is required.

Peru

 In March and September of 2011, Planeta Oceano, conducted rapid assessments of the mobulid fisheries along the north coast of Peru in the Tumbes & Piura regions. One family of fishermen (one boat crewed by a father and his grown sons) directly target M. birostris, while two other fishermen are said to occasionally target mantas. The family estimates annual total landings of 100 to 120 M. birostris, with other targeted and incidental catches estimated at 50 to 100 manta rays, for a total of 100 to 220 M. birsostris. Mobula landings are estimated at ~ 8,000 based on observed catches, bringing total mobulid landings to ~ 8,150 per year.

Across the border in Ecuador, manta and mobula species are protected under Ecuadorian law, but these same animals are targeted when they migrate south to Peru. Because the family that targets manta rays has expressed willingness to participate in future conservation programs for manta rays, the outlook for protection here (at least for manta rays) is promising. Peru is also a party to the CMS Convention, which now lists M. birostris on its Appendices I and II and obligates parties to pursue measures to protect this species.

Indonesia

Directed manta and mobula ray fisheries are confirmed to exist in Lombok, Lamakera, Lamalera, as well as in other villages in Alor and perhaps in many other areas2. Manta and mobula rays are also landed as bycatch in local gillnet fisheries for tuna, and have been observed at markets in Pelabuhanratu in West Java, Cilacap in Central Java, and Kedonganan in Bali3. Species found in Indonesian fisheries include M. birostris, M. alfredi, M. japanica, M. tarapacana, M. thurstoni, and M. kuhlii4. Landings estimates from all Indonesian mobulid fisheries combined are more than 1,300 manta rays (M. birostris) and more than 3,500 mobula rays (various species). Indonesia appears to have the largest landings of M. birostris of any of the documented fisheries.

Lamakera Investigation: In June to July 2011, a rapid assessment of the fishery was conducted in Lamakera, a village on Lembata Island in the Alor region. This investigation relied on direct observation and interviews with a wide variety of community members from Lamakera and surrounding villages, and is the first known assessment since Dewar’s description of the fishery published in 2002.

When manta rays are spotted in the area, villagers go out en-masse, aided by mobile phones to facilitate communications on the locations of the sightings. As soon as a boat gets into range of a manta, a crewmember plunges a steel, barbed spearhead attached to a long bamboo shaft into the manta ray’s back. A rope is connected to the barbed spearhead, which releases from the shaft and line is given out for the manta ray to run. The manta ray takes about a half hour to tire during which time the crew chants an ancestral song they believe will stop the manta from escaping. They insert long knives into the head region and then push a long metal rod into the brain or heart to kill the animal. The body is secured with ropes and gaffs and the entire crew hauls the manta ray onboard, where they cut off the pectoral fins, remove the gills and cut off the head.

Lamakera’s annual catch for 2010 based on all sources interviewed was 660 manta rays (M. birostris) and 330 mobula rays (M. tarapacana), for a combined catch of 990 mobulids. The catch trend appears to have declined significantly since the Dewar 2002 estimates of 1,050 to 2,400 manta rays landed each year, a strong indication that overfishing has significantly depleted manta ray populations that migrate along this corridor.

Lombok Investigation: The Lombok assessment of manta and mobula ray fisheries and trade was conducted in the Tanjung Luar market over six visits during varying seasons in 2007, 2009, 2010 and 2011. Both fishermen and the local processing facility reported that manta and mobula ray catches had declined dramatically in recent years and that the average manta ray size was now less than half of what it used to be. Based on these surveys, approximately 300 manta rays (M. birostris) and 1,000 mobula rays (various species) are landed annually in this port. A survey conducted in Tanjung Luar from 2001 to 2005 reported landings of ~ 1,600 mobulids per year and sales of adult manta rays from 4.4m to 4.8m DW5, confirming the fishermen’s reports of decreases in both numbers and size of manta rays landed over the past few years.

Fishermen and processors indicated that the gills were the primary value, with manta gills more valuable than the smaller mobula gills. Trade routes point to Chinese buyers in Surabaya and Jakarta. The rest of the animal is of nominal value and without the gill raker revenue, the income from meat and skin sales would not even cover the fuel expended to hunt these animals.

In Lamakera, where villagers have hunted these animals for many years, tradition also plays a role in the ongoing exploitation of manta and mobula rays, even prior to the gill raker trade. The excitement of the hunt and of returning with a large conquered sea animal was evident in recent investigations. The advent of the gill raker trade, however, transformed this fishery from a small-scale artisanal practice to a large-scale commercial enterprise.

Southern China

In 2011, investigators visited a shark processing plant in Puqi, Zhejiang Province of China, which had been suspected as a major processor of manta and mobula ray gill rakers. This plant processes whole manta and mobula rays shipped from a nearby port in Shipuzhen, and sells dried gill rakers directly to buyers in Guangdong (estimated 500 kg M. birostris; 1000 kg M. japanica annually). The manta and mobula ray carcasses are sent to a plant in Shangdong, where the meat is ground up for fishmeal and the cartilage is processed to make chondroitin sulfate supplements, for export to Japan and Britain.

The plant manager reported that 500 kg of large manta (whole) yields ~ 2.5 kg of dried gill rakers. Based on conversion calculations (5 kg of dried gill raker per average mature M. birostris and .5 kg per average small mobula), an estimated 100 manta rays (M. birostris) and 2,000 mobula rays (M. Japanica) are processed annually in this port.

Africa

While little published data is available for African mobulid fisheries, significant threats to manta and mobula rays may exist in several countries on the east and west coasts of Africa.

In Mozambique it is estimated that 20 to 50 M.alfredi are taken by subsistence fishermen annually just along a ~ 100 km area6. An extensive and ongoing observational study on manta abundance in Southern Mozambique also reports an 80% decline in Manta alfredi over the last 9 years. In 2003 and 2004 there was an 83% chance of seeing a manta ray on a dive, but sighting frequency has steadily declined over time to only a 31% chance of seeing mantas on dives in 2011. The number of individuals seen per dive has declined drastically as well, from an average of 6.8 individuals in 2003 and 2004 to 0.6 individuals per dive in 20117.

In Ghana, Dixcove is known for its seasonal harvest of manta rays8; and a year round large mesh drift gillnet fishery targeting tuna, sharks, billfish, manta rays and dolphins, has also been reported9. Additional investigation to determine the extent of fisheries and trade for manta and mobula species in Africa is critically needed.

Thailand

Dive operators in the Similan Islands located in the Andaman Sea, have witnessed increased fishing for manta and mobula rays, even in Thai national marine parks, and have reported steep declines in manta ray sightings10.

Review of the largest manta ray photo identification database for this region has revealed a significantly higher proportion of individuals with net and line injuries than anywhere else in the world, except for mainland Ecuador (due to illegal fishing for wahoo in a major M. birostris aggregation area). This photographic evidence strongly supports anecdotal reports that fishing is having a major impact on the manta ray population in the area11.

These observations present the possibility of significant population declines of M. birostris and M. alfredi in the Similan Islands due to targeted fishing. With fisheries data lacking on manta and mobula ray landings, further investigation is required to properly assess the extent and impact of mobulid fisheries in Thailand.

Phillipines

Some areas, such as Pamilacan Island in Bohol, have a long history of hunting manta rays along with whales and whale sharks12. Following the passage of a ban on catching dolphins and whales in late 1992, whaling communities in the Bohol Sea area shifted more of their efforts to whale sharks and manta rays, and in 1998 twenty six villages were involved in manta and mobula ray fisheries. During the 1995-6 season, 1,000 manta and mobula rays were landed. Interviews with fishermen during a 1996 survey revealed that manta ray catches had declined by 50% over the past 30 years13.

Today the ban on catching and selling of manta rays is still in place, but enforcement varies and the cultural practice of eating manta ray meat persists in some areas14. Traders in Hong Kong continue to report the Philippines as a supplier of dried gill rakers, indicating that an active gill raker trade may still continue in the Philippines15. Further investigation is required to properly assess the extent of mobulid fisheries and the connection to the gill raker trade.

Mexico

In May 2007, Mexican Official Standard Rules NOM–029–PESC– 2006 was enacted, providing specific protection for mobulid rays (M. birostris, Mobula spp.). No current reports were identified relating to targeted fisheries for giant manta rays (M. birostris) in the Sea of Cortez, but fisheries for mobula species are reported to be prevalent, particularly in El Sargento and Santa Rosalia, where thousands of mobulas are reportedly taken every summer16.

Further investigation to determine the extent of exploitation of manta and mobula rays in Mexico is needed. Bycatch may be significant due to the high volume of commercial fisheries using drift gillnets and longlines. No definitive evidence of a gill raker trade has been reported in Mexico, but further investigation is warranted to confirm this.

Ecuador

During the first half of 2010, prior to Ecuador’s ban on fishing manta and mobula rays, landings of 6,946 mobula rays were recorded17.

The Ecuadorian government has been a leader in manta and mobula conservation, evidenced by the strict ban on the landing and sale and manta and mobula rays enacted in August 2010 and their successful proposal to list M. birostris on Appendices I and II of the international CMS convention. Since enactment of the 2010 ban, landings of manta and mobula rays appear to have stopped.

In a major M. birostris aggregation area where illegal drift gillnet and longline fisheries targeting wahoo are still prevalent, researchers have observed large numbers of manta rays with life threatening or debilitating injuries from entanglement18. Further investigation and monitoring is recommended to better understand the current level of mobulid bycatch mortality associated with these fisheries.

 

References & Resources

1 - FAO 2009; Lack & Sant 2009

2 - Dewar 2002, White et al 2006, Barnes 2005, Setiasih 2011, A. Miners pers. comm.

3 - White et al. 2006b.

4 - White et al 2006, Setiasih 2011, G. Stevens pers. comm.

5 - White et al. 2006b,

6 - Marshall et al. 2011.

7 - A. Marshall pers. comm.

8 - Essumang 2010;

9 - Reeves et al. 2003.

10 - R. Parker pers. comm.

11 - A. Marshall pers. comm.

12 - Acebes 2009.

13 - Alava et al. 2002.

14 - Gamil and Gamil 2010.

15 - P. Hilton pers. comm.

16 - M. McGettigan, SeaWatch pers. comm.

17 - A. Baquero, Equilibrio Azul, unpubl.

18 - A. Marshall pers. comm.

 

Acebes, J.M.V. 2009. Historical whaling in the Philippines: origins of ‘indigenous subsistence whaling’, mapping whaling grounds and comparison with current known distribution: a HMAP Asia Project Paper. Asia Research Center/HMAP, 161. 37pp.

Alava, E.R.Z., Dolumbaló, E.R., Yaptinchay, A.A., and Trono, R.B. 2002. Fishery and trade of whale sharks and manta rays in the Bohol Sea, Philippines. In: Fowler, S.L., Reed, T.M., Dipper, F.A. (eds) Elasmobranch Biodiversity, Conservation and Management: Proceedings of the International Seminar and Workshop. Sabah, Malaysia, July 1997, pp 132–148

Barnes, R.H. 2005. Indigenous use and management of whales and other marine resources in East Flores and Lembata, Indonesia. Senri Ethnological Studies, 67: 77-85.

Dewar, H. (2002). Preliminary report: Manta harvest in Lamakera. p. 3 p. Oceanside, USA: Report from the Pfleger Institue of Environmental Research and the Nature Conservancy.

Essumang, D. 2010. First Determination of the Levels of Platinum Group Metals in Manta birostris (Manta Ray) Caught Along the Ghanaian Coastline. Bulletin of Environmental Contamination and Toxicology, 84(6): 720-725.

FAO (2009). FAO Fishstat Capture Production Database 1602 1950-2007. Available at www.fao.org/fishery/statistics/global-capture-production/en.

Gamil, J.T. and Gamil, A.P. 2010. Rescuer of manta rays. Philippine Daily Inquirer, November 3, 2010.

Lack, M and Sant, G. 2009. Trends in global shark catch and recent developments in management. TRAFFIC International, 33 pp.

Marshall, A., Kashiwagi, T., Bennett, M.B., Deakos, M., Stevens, G., McGregor, F., Clark, T., Ishihara, H. & Sato, K. 2011. Manta alfredi. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>.

Reeves, R.R., Smith, B.D., Crespo, E.A., and Notarbartolio di Sciara, G. (eds) 2003. 2002-2010 Conservation Action Plan for the World’s Cetaceans: Dolphins, Whales and Porpoises. IUCN/SSC Specialist Group, 147 pp.

Setiasih, N. 2011. Indonesia Fishery Investigation. Manta Ray of Hope, 15 pp.

White, W. T., Giles, J., Dharmadi, and Potter, I. C. 2006 b. Data on the bycatch fishery and reproductive biology of mobulid rays (Myliobatiformes) in Indonesia. Fisheries Research, 82(1-3), 65-73.

White, W.T., Clark, T.B., Smith, W.D. & Bizzarro, J.J. 2006. Mobula japanica. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>

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