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PROTECT: Manta Rays

Since the Manta Ray seems to be such a mystery to most people, exploring the facts about them can help you to see them for what they really are.

These are fascinating creatures that live in the water.

  • They can be up to 25 feet in length and weight as much as 5,000 pounds.
  • Some types of Manta Rays engage in the process of migrating.
  • They can lose their protective mucus membrane if they are touched by humans.
  • The Manta Ray has the largest brain to body ratio of all sharks and rays on Earth.
  • You will very rarely find any Manta Ray in captivity due to their size. They are currently only found in four aquariums in the world.
  • The average life span for a Manta Ray is 20 years.
  • They are very close relatives of the shark. Ironically, sharks as well as whales are their main predators. They are also closely related to the stingray but they don’t have a stinger.
  • They are amazing when it comes to the acrobatics that they display.
  • The Manta Ray is classified as a fish. It is one of the largest and it continues to be one that we know the least about.
  • They don’t have a skeleton that is made from bone.
  • The smallest species of Manta Ray is the Mobula Diabolis. It is only about 2 feet in length.
  • There are myths that the Manta Ray will consume people but they are false. These are very gentle creatures that are able to get close to humans without harming them.
  • The Manta Ray is only surpassed in size in the marine world by sharks and whales.
  • There are only four of them found in the world that are in captivity. They do well in that environment but they are so large it is very hard to justify the cost of keeping them.
  • One of the reasons why people used to think that the Manta Ray was dangerous is because the body appears to be like a huge bat.
  • The open fins of a Manta Ray can be more than 20 feet in length.
  • While the Manta Ray has many rows of sharp teeth, they aren’t used for eating. Instead they have a filtering system.
  • The Manta Ray doesn’t have a nose.
  • The name Manta means blanket, and the fact that this creature looks like a blanket as it moves in the water is part of the namesake.
  • The mouth of the Manta Ray is located on the top of the head instead of on the bottom.
  • They are the only jawed vertebrates that also have limbs.
  • Many people view the Manta Ray as a shark that has been flattened out due to the overall anatomy that it features.
  • The movement of the fins through the water is very similar to that of a bird flapping its wings.
  • Many people assume that the Manta Ray is dangerous due to the fact that the Sting Ray is. However, they don’t have a stinger at all.
  • Many Manta Rays blend in well at the shoreline. They tend to get stepped on by people that don’t have a clue what is below their feet.
  • They are extremely fast swimmers and also considered to be one of the most graceful as they move around. If you don’t look quickly though one can be gone before you realize it was there.
  • Manta Rays are an endangered species and are listed by the IUCN 
 

Manta Rays and Global Warming

Manta Rays are among the animals living in the water that are affected by global warming. It has had some positive effects on them as well as some negative impacts that we will explore. Since the Manta Ray needs warmer water to live in, their habitat has been able to expand due to global warming. Yet many of them live in lakes, swamps, and lagoons. These bodies of water can easily dry up due to the hotter temperatures. Then the Manta Rays die as they have no water to move around in.

It can become harder for the Manta Ray to find food in its natural environment. Thanks to global warming they can freely move to other areas and migrate to find food. Yet this process makes them more susceptible to becoming prey for sharks and whales. The overall size of these animals may decrease due to global warming. This because they have to learn to survive on less food.

It also increases their risk of being injured or killed in fishing nets that are part of commercial operations. As their need for food continues to be neglected, the Manta Ray is going to move where it can find large amounts of it. This is also going to be where the commercial fishing nets are set up to yield large amounts being captured daily.

There is also research that indicates warmer temperatures are going to result in the Manta Ray continually getting smaller as the decades continue to fall upon us. This is due to the fact that they will then be able to survive on less food. However, many researchers also believe that they will become prey to many more animals in the water if they are smaller. Right now they seem to get left alone by most due to their very large size.

Many Manta Rays also end up coming into contact with boats on the water. As the outside temperatures heat up more people use the water to cool off. They are very curious creatures so they tend to jump around the boats. They can be struck so that injuries or death occurs. Since they migrate so much it is hard for authorities to block off areas where these animals may frequently be from boat traffic.

The increased risk of meeting up with people in the water is a problem too. Those on guided expeditions already know not to touch the Manta Rays as this can expose them to viruses and bacteria. However, many people that just happen to be diving in the water around them don’t realize the danger that they are putting these animals in.

When you also take into consideration that bacteria, parasites, and viruses are going to grow more rapidly in warm water, you are putting the livelihood of the Manta Rays at risk. There is a very good chance large numbers of them will be wiped out as such problems continue to expand.

Some researchers believe that studying Manta Rays and global warming at the same time will give us some guidance about how other similar species including sharks are going to be affected. Since the Manta Rays don’t pose a threat to humans they are less likely to be a problem when it comes to research then sharks.

Global warming is a huge concern for all life out there including Manta Rays and humans. Taking action now to reduce the effects of it is a responsibility that all of us must accept. Younger generations need to learn the problems that have been created as well so that they don’t recreate them.

IUCN RED LIST: VULNERABLE

http://www.iucnredlist.org/apps/redlist/details/198921/0

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http://www.southernfriedscience.com/?p=11846Manta rays are true gentle giants; though they can grow more than 20 feet wide from wingtip to wingtip, they eat only plankton. Swimming with these animals is a rare thrill for SCUBA divers, and manta-viewing ecotourism is worth over $100 million each year. Like many species of sharks, manta rays grow slowly and reproduce rarely. According to Dr. Nick Dulvy of the IUCN Shark Specialist Group, “ they give birth to an average of one offspring every two years…they are a long-lived species with little capacity to cope with modern fishing methods.”  They also migrate across huge distances, regularly crossing between national boundaries and spending much of their time on the high seas, making management difficult.Although their biology cannot support a large-scale fishery and their behavior makes any fishery inherently difficult to manage, manta rays are very much in demand. At least part of them is: their gill rakers. According to Lucy Harrison, program officer for the IUCN Shark Specialist group, “Increasing demand for these fishes’ filter-feeding system for traditional Chinese medicinal purposes, especially in Hong Kong, is rapidly driving down their population everywhere.”By some measures, the global population of manta rays has declined by more than 30% in recent decades, with some local populations facing much larger declines.  Earlier this week, an IUCN Shark Specialist Group team led by Andrea Marshall has concluded that both species of manta ray (the giant manta Manta birostris and the reef manta Manta alfredi) should be declared Vulnerable* to extinction.The IUCN Shark Specialist Group recommends that several steps be taken to protect mantas from further population declines. These include discussing the value of international conservation treaties, such as CMS and CITES, for both species as well as national-level policy changes in countries that fish for mantas. 

 

Giant Mantas & Reek Mantas

Previously, the genus Manta was considered monotypic by most authors. The genus was recently re-evaluated and split into two species, the Reef Manta Ray (Manta alfredi) and the Giant Manta Ray (Manta birostris) (Marshall et al. 2009). Genetic evidence further confirms the existence of two separate species (Kashiwagi et al. 2008, Ito and Kashiwagi 2010). Both species have worldwide distributions. Manta species are sympatric in some locations and allopatric in other regions (Kashiwagi et al. 2011).

Reports are often mixed as the splitting of the genus occurred very recently (2009). Historical reports can often be confusing as well without adequate descriptions or photographs. Care should be taken when using reports or accounts of the Giant Manta Ray that they are not referring to the Reef Manta Ray (or vice versa).

Melanistic (black) and leucistic (white) colour morphs occur in both species of Manta(Marshall et al. 2009). Variant colour morphs often contributed an added degree of confusion when attempting to discriminate between species of Manta in the field or in photographs, especially when close examination was not possible. It should be noted that these colour morphs could be a possible source of error, resulting in mis-identifications in future studies or surveys of distribution.

Justification:
The Giant Manta Ray (Manta birostris), the largest living ray, has a circumtropical and also semi-temperate distribution throughout the world’s major oceans, however within this broad range, actual populations appear to be sparsely distributed and highly fragmented. This is likely due to the specific resource and habitat needs of this species. Overall population size is unknown, but subpopulations appear to be small (about 100–1,000 individuals). Only recently separated from the Reef Manta Ray (M. alfredi), little is currently known about this ray except that it is elusive and potentially highly migratory.

The degree of interchange of individuals between subpopulations is unclear but is assumed to be low as there are currently no data that support such interchange despite active efforts to do so. As such, the decline of these small subpopulations may result in regional depletions or extinctions with the reduced possibility of successful recolonization. To aggravate this situation, this species has a very conservative life history with an extremely low reproductive output (one pup per litter). These biological constraints would also contribute to its slow or lack of recovery from population reductions.

Currently this species has a high value in international trade and directed fisheries exist that target this species in what is certain to be unsustainable numbers. Artisanal fisheries also exist that target this species for food and medicine. Individuals are also taken as bycatch in everything from large-scale fisheries to shark control programs/bather protection nets.

The rate of population reduction appears to be high in several regions, as much as 80% over the last three generations (approximately 75 years), and globally a decline of >30% is strongly suspected. Sustained pressure from fishing (both directed and bycatch) has been isolated as the main cause of these declines. Certain monitored subpopulations appear to have been depleted, such as in the Philippines, Indonesia, and parts of Mexico and are believed to be decreasing in other areas such as India and Sri Lanka as a result of sustained pressure from fishing. Of particular concern is the targeting of this species at critical habitats or well-known aggregation sites where numerous individuals can be targeted with relatively low catch-per-unit-effort.

Dive tourism involving this species is a growing industry and it has been demonstrated that sustainable tourism significantly enhances the economic value of such species in comparison to short-term returns from fishing. Tourism related industries can also negatively impact individual behaviour, entire populations and critical habitat for this species, thus the responsible development of these industries is recommended.

Range

Circumglobal in tropical and temperate waters, this species has a widespread distribution. The Giant Manta Ray has been documented to occur as far north as southern California and New Jersey on the United States west and east coasts, respectively, Mutsu Bay, Aomori, Japan, the Sinai Peninsula, Egypt and the Azores Islands in the Northern Hemisphere and as far south as Peru, Uruguay, South Africa and New Zealand in the Southern Hemisphere.

In a few locations, including Mozambique, the Giant Manta Ray is sympatric with the Reef Manta Ray. When they occur together these species typically exhibit different habitat use and movement patterns (Marshall et al. 2009, Kashiwagi et al. 2011).

The Giant Manta Ray appears to be a seasonal visitor to coastal or offshore sites. While this species seems more solitary than the Reef Manta Ray, Giant Manta Rays are often seen aggregating in large numbers to feed, mate, or clean. Sightings of these giant rays are often seasonal or sporadic but in a few locations their presence is a more common occurrence. Observations of the Giant Manta Ray at aggregation sites such as the Similan Islands, Thailand; northeast North Island, New Zealand; Laje de Santos Marine Park, Brazil; Isla de la Plata, Ecuador; and Isla Holbox, Mexico, indicate that this species is a regular seasonal visitor, with sightings only during specific, predictable times of the year (Duffy and Abbott 2003, Luiz et al. 2009, A. Marshall pers. obs. 2011).

Population

This species is not regularly encountered in large numbers and, unlike the Reef Manta Ray do not often appear in large schools (>30 individuals) when feeding. Overall they are encountered with far less frequency than the smaller Manta species, the Reef Manta Ray, despite having a larger distribution across the globe.

Due to the global nature of their individual distributions, absolute population sizes will always be difficult to assess. Currently, the overall total global population sizes of both these species are unknown, but subpopulations appear, in most cases, to be small (less than 1,000 individuals). The degree of interchange of individuals between subpopulations is unclear but is assumed to be low, as there are currently no data that support such interchange, despite active efforts to do so (A. Marshall et al. unpubl. data 2011).

 

habitat

The Giant Manta Ray occurs in tropical, sub-tropical and temperate waters of the Atlantic, Pacific and Indian Oceans. Commonly sighted along productive coastlines with regular upwelling, oceanic island groups and particularly offshore pinnacles and seamounts. The Giant Manta Ray is commonly encountered on shallow reefs while being cleaned or is sighted feeding at the surface inshore and offshore. It is also occasionally observed in sandy bottom areas and seagrass beds.

A global investigation of major aggregation sites revealed that the Giant Manta Ray may be a more oceanic and a more migratory species than the Reef Manta Ray (A. Marshallet al. unpubl. data). Rare or seasonal sightings of the Giant Manta Ray at locations such as northern New Zealand (Duffy and Abbott 2003), southern Brazil (Luiz et al. 2009) and Uruguay (Milessi and Oddone 2003), the Azores Islands, the Similan Islands, Thailand (A. Marshall unpubl. data 2011) and the eastern coast of the United States (Bigelow and Schroeder 1953), suggests that this species undergoes significant seasonal migrations.

Despite these data, preliminary satellite tracking studies and international photo-identification matching projects have suggested a high degree of fragmentation between regional populations of this species, suggesting that movements across ocean basins may be rare. Satellite tracking results have been able to reveal that the Giant Manta Ray is capable of large migrations (over 1,100 km straight line distance) and have monitored individual movements across international borders, across large bodies of water, and into international waters (A. Marshall et al. unpubl. data 2011, R. Rubin pers. comm. 2009). Satellite tracking studies using archival PAT tags have registered movements of the Giant Manta Ray from Mozambique to South Africa (a distance of 1,100 km), from Ecuador to Peru (190 km), from the Yucatan, Mexico into the Gulf of Mexico (448 km). This species is capable of deep dives and has been both seen at depth and tracked down to depths exceeding 1,000 metres (A. Marshall et al. unpubl. data 2011).

The Giant Manta Ray reaches disc widths (DW) of at least 700 cm, with anecdotal reports up to 910 cm DW (Compagno 1999, Alava et al. 2002). Size at maturity for the Giant Manta Ray may vary slightly throughout its range, but males in southern Mozambique mature at approximately 400 cm DW while females appear to mature well over 400 cm DW (Marshall 2009). In Indonesia, data from fisheries dissections suggest that in that region male Giant Manta Rays mature at 375 cm DW, while females may mature by approximately 410 cm DW (White et al. 2006).

The Giant Manta Ray appears to be a relatively long-lived species. Although the actual longevity of the species remains unknown, photographic databases have re-sighted individuals up to a 20 year period (Rubin 2002, G. Kodja unpubl. data 2010). Natural mortality is thought to be low (other than in juveniles), although limited predation from large sharks does occur (Marshall 2009).

Generation time is suspected to be 25 years based on conservative estimates of life history parameters from the Reef Manta Ray. Female mantas are thought to mature at 8–10 years of age and longevity is estimated to be at least 40 years. Generation time is the average age of adults which can be approximated as halfway between age at first maturity and maximum age. Thus female mantas may be actively breeding for 30 years and the age at which 50% of total reproductive output is achieved would be approximately 24–25 years.

Copulation has been documented off the Ogasawara Islands, Japan and is believed to occur in the summer months (Yano et al. 1999b). Two pregnant individuals have been registered and photographed in southern Mozambique although a breeding season at this location has not been established (Marshall 2009). There is little information on the reproductive biology or ecology of this species although reports of litter size are consistently of a single offspring (Coles 1916, Beebe and Tee-Van 1941, Bigelow and Schroeder 1953).

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