Manta Rays, Mozambique
Project Leader: Andrea Marshall
Background
The International Union for the Conservation of Nature (IUCN) currently lists manta rays (Manta birostris) as ‘near threatened’. It’s known that several populations around the world are severely depleted, but not enough scientific work has been carried out to properly assess the species as a whole. Almost nothing is known about their population ecology, use of critical habitat, movements or reproduction, all of which are vital in order to accurately assess the state of the species.
The SOSF-funded manta ray project has been a tremendous success over the past five years, culminating in the completion of Andrea Marshall’s thesis in 2008. The undoubted highlight was the discovery of at least one new species of manta ray (Manta birostris) which received world wide press attention and is reported on below. This is the biggest news to date to come out of ray research, and its importance is the marine equivalent of finding an unknown species of elephant. The discovery has implications that go far beyond the breaking news of scientific journals, since it will impact on conservation policies for the species. That said, Andrea and her team have also shed light on many aspects of manta ray biology that were previously absent from the scientific literature, such as detailed reproductive parameters, biology and behavior. The data compiled will directly help in assessing their current conservation status and planning future management efforts.
The SOSF-funded manta ray project has been a tremendous success over the past five years, culminating in the completion of Andrea Marshall’s thesis in 2008. The undoubted highlight was the discovery of at least one new species of manta ray (Manta birostris) which received world wide press attention and is reported on below. This is the biggest news to date to come out of ray research, and its importance is the marine equivalent of finding an unknown species of elephant. The discovery has implications that go far beyond the breaking news of scientific journals, since it will impact on conservation policies for the species. That said, Andrea and her team have also shed light on many aspects of manta ray biology that were previously absent from the scientific literature, such as detailed reproductive parameters, biology and behavior. The data compiled will directly help in assessing their current conservation status and planning future management efforts.
In the field
Manta rays
are the largest of over 500 different species of rays and skates; their
triangular pectoral fins can span almost 8m in width and weight reach
over 2,000kg. Andrea has developed a systematic method of identifying individual mantas by their ventral (underside) spot patterns, which are unchanging and present from birth. This has allowed her to establish an identification database based on a single reef site in Mozambique which now contains over 900 individuals, making it the largest and most in-depth manta dataset in the world. When combined with population modeling and behavioural observations, her data suggests that southern Mozambique may host the largest manta population in the world, with possibly 1000 individuals in the area Andrea works in alone.
Acoustic tagging equipment and listening stations sponsored by SOSF have enabled Andrea to examine how individual manta rays use critical habitats, like cleaning stations, along the coastline. Andrea and her group have also begun the genetic sampling of the entire local manta population. Cutting edge genetic research in conjunction with researchers at the University of Queensland is also being planned; in a first of its kind, its focus will be on the relatedness within the local manta population. With the continued assistance of SOSF, Andrea is also conducting comparative research by collecting DNA samples in Mexico, Japan, Yap, Thailand, Indonesia and Australia.
Acoustic tagging equipment and listening stations sponsored by SOSF have enabled Andrea to examine how individual manta rays use critical habitats, like cleaning stations, along the coastline. Andrea and her group have also begun the genetic sampling of the entire local manta population. Cutting edge genetic research in conjunction with researchers at the University of Queensland is also being planned; in a first of its kind, its focus will be on the relatedness within the local manta population. With the continued assistance of SOSF, Andrea is also conducting comparative research by collecting DNA samples in Mexico, Japan, Yap, Thailand, Indonesia and Australia.
An incredible discovery
The highlight of Andrea's research has been the confirmation of the existence of a second species of manta. Although divers have previously noted variations in physical appearance, they were believed to be the same species. Her suspicions aroused, Andrea began studying other populations across the globe and, through genetic and morphological analysis, she identified a second, and possibly a third, species of manta ray that exists across temperate, tropical and subtropical waters worldwide. The two species have mainly overlapping distributions, but their lifestyles differ greatly: one is migratory and the other is resident to particular areas along coastlines. Other differences between the two lie in their color, skin texture, reproductive biology and the presence of a non-functioning type of sting on the tail of one of the species.
The smaller, more commonly known, manta rays reside in the same areas year round and are often encountered near coral reefs where they congregate to be cleaned by parasite-eating fish in locations such as Hawaii, the Maldives, Mozambique, Australia, Japan and the Island of Yap. Due to their residential nature, they face a number of threats including habitat degradation, harassment by boat traffic and even divers who interact with them at critical habitats such as cleaning stations and breeding areas. They also fall victim to ghost nets and are killed alongside many other marine creatures as by-catch. Protective measures within countries need to be enforced to avoid the regional extinction of manta ray populations becoming a possibility.
Far less is known about the larger species, as it appears to be more migratory and elusive, shying away from divers rather than seeking interaction as its smaller cousin often does. Andrea has only ever witnessed it arriving at sea-mounts or at particularly productive areas along the coastline to feed on plankton before disappearing into the blue once again. Since this larger, ocean wanderer seemingly knows no borders, collaboration between countries for its protection and conservation management is essential. Little is known about its behavior or migratory patterns, though it appears to be targeted heavily by fisheries, particularly in southeast Asia, where thousands are killed each year. Andrea’s next phase of research will take her to Indonesia, Thailand and the Philippines to help shed some light on the unknown parameters of the species needed for any considered protection planning.
The smaller, more commonly known, manta rays reside in the same areas year round and are often encountered near coral reefs where they congregate to be cleaned by parasite-eating fish in locations such as Hawaii, the Maldives, Mozambique, Australia, Japan and the Island of Yap. Due to their residential nature, they face a number of threats including habitat degradation, harassment by boat traffic and even divers who interact with them at critical habitats such as cleaning stations and breeding areas. They also fall victim to ghost nets and are killed alongside many other marine creatures as by-catch. Protective measures within countries need to be enforced to avoid the regional extinction of manta ray populations becoming a possibility.
Far less is known about the larger species, as it appears to be more migratory and elusive, shying away from divers rather than seeking interaction as its smaller cousin often does. Andrea has only ever witnessed it arriving at sea-mounts or at particularly productive areas along the coastline to feed on plankton before disappearing into the blue once again. Since this larger, ocean wanderer seemingly knows no borders, collaboration between countries for its protection and conservation management is essential. Little is known about its behavior or migratory patterns, though it appears to be targeted heavily by fisheries, particularly in southeast Asia, where thousands are killed each year. Andrea’s next phase of research will take her to Indonesia, Thailand and the Philippines to help shed some light on the unknown parameters of the species needed for any considered protection planning.
Reproduction
Little is known about the reproductive cycle of mantas, but Andrea’s observational work over the last 5 years has now shown that on average females produce 1 pup every 2 years. This makes them inherently vulnerable to population crashes and human pressures as their biology acutely limits the ability for their populations to recover from a loss in numbers.
Predation
Although in other parts of the world, only 5-10% of mantas exhibit bite wounds, Andrea has found that an extraordinary 75% of the observed manta population in southern Mozambique have bites attributable to shark attacks. Previous to this discovery it was thought that mantas had no major natural predators; it now appears sharks may play a significant role in influencing and regulating manta populations.
Eco-toursim & conservation
As a result of hunting and war, large land animals are scarce in Mozambique. This costs the country millions in lost tourism revenue each year as it is bypassed by the ‘safari circuit’. However, Mozambique may have one of the largest populations of mantas and whale sharks in the world, presenting a major addition to ecotourism in southern Africa and a point of difference for Mozambique itself.
Aims & objectives
These immensely charismatic animals are now the focus of a growing tourism industry in the south of the country, providing much-needed employment to the Mozambican people. As a consequence the work of The Manta Ray & Whale Shark Research Group in conducting their world-leading research is more vital then ever. Their scientific programs continue to examine the effect of eco-tourism on local manta populations, and have already shown that sightings of mantas at popular dive sites have been decreasing over time. This suggests that while eco-tourism might not be directly threatening the mantas, it might possibly be a factor in where they choose to spend significant periods of time.
Andrea and her team also continue to use all the data they collect to put pressure on illegal shark fishing activities and promote their conservation worldwide. With the help of the new SOSF dedicated research boat, they have been able to assist local government officials in banning and confiscating local long-lines and gill nets, which unsustainably kill hundreds of sharks and rays (including mantas) each month.
Andrea and her team also continue to use all the data they collect to put pressure on illegal shark fishing activities and promote their conservation worldwide. With the help of the new SOSF dedicated research boat, they have been able to assist local government officials in banning and confiscating local long-lines and gill nets, which unsustainably kill hundreds of sharks and rays (including mantas) each month.
Project Update: 2008
In 2008, supported largely by the manta ray (Manta birostris) research sponsored by the SOSF, the Manta Ray & Whale Shark Research Centre in Mozambique has expanded to form a new Mozambican Foundation, the Foundation for the Protection of Marine Megafauna. Using data acquired from the region and beyond, this Foundation seeks to educate local communities, school children, and government about the importance of the marine environment and its resources. In partnership with other NGOs and with support from local and national government, the Foundation will use research data to formulate conservation efforts and management plans and will promote the sustainable development of the Mozambican coastline.
Andrea's project now holds probably the largest in-depth scientifically recorded manta database in the world with 900 individuals recorded of which one fifth has been DNA sampled. Research from 2008 has proved to be especially significant, as the results of the last 5 years of study were published and presented at 2008's American Elasmobranch Society Meeting.
The work is also scheduled to broaden from the concentration of one particular species of Manta ray to include the more common species which are being particularly targeted by fisheries around Indonesia, Thailand and the Philippines. Such studies aim to answer some important biological questions such as the fecundity, gestation period and reproductive periodicity of manta populations; in addition it is hoped to establish the quantity of manta rays taken in these areas of south-east Asia to determine the sustainability of these direct fisheries.
Andrea's project now holds probably the largest in-depth scientifically recorded manta database in the world with 900 individuals recorded of which one fifth has been DNA sampled. Research from 2008 has proved to be especially significant, as the results of the last 5 years of study were published and presented at 2008's American Elasmobranch Society Meeting.
The work is also scheduled to broaden from the concentration of one particular species of Manta ray to include the more common species which are being particularly targeted by fisheries around Indonesia, Thailand and the Philippines. Such studies aim to answer some important biological questions such as the fecundity, gestation period and reproductive periodicity of manta populations; in addition it is hoped to establish the quantity of manta rays taken in these areas of south-east Asia to determine the sustainability of these direct fisheries.