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Manta Ray - a threatened species 0708

Page history last edited by PBworks 12 years, 11 months ago
 Manta Ray - a threatened species
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By: Benjamin Hestevold

 


 

 

Description and Rationale

 

 

 

 

 

 

 

Generally, very little is known about the origin, life biology, and the history of the manta rays. The first description of the manta ray found was in 1798 by Dondorff. Throughout the Philippines, the numbers of existing manta rays have been continually decreasing, and have now entered into the threatened group of species. Licensed manta ray fishers in the Philippines use 30 meter high, one-kilometer long drift nets to catch these rays, but dolphins and endangered turtles are also caught and killed. When it was found that the manta rays, along with the whale shark, were becoming decimated in the Philippines, the BFAR banned the hunting of manta rays and whale sharks. But four years later the ban was removed due to misguided political pressure, and now manta rays are again hunted as a delicacy.

 

What will be the impact on the environment if the manta rays do become extinct? Will it create a big hole in the food chain resulting in further damage? Will predators to the manta ray be left without a food source? Are there any natural factors that harm the survival of this species? Besides hunting the manta rays, are there ways that humans reduce the number of manta rays throughout the planet? Do the manta rays create harm to any possible part of its environment? Are there ways to increase the population of the manta rays?

 

In the Philippines the manta rays are hunted by fishermen because its meat is considered a delicacy. Could fishermen who hunt these rays for money and their own survival change their target of fish? Also, could another species of fish replace the manta rays as a delicacy? Could it be possible for them to receive at least the same amount of money hunting an abundant species instead? Because of the increasing pressure on the Filipino fishermen they turn towards hunting the manta rays as an exchange meat source. Would it be possible to find an alternate source of meat for these fishermen, so the manta rays would be left in peace? Also, would it be possible to teach Filipino fishermen to make their own fish plantations, could they harvest and grow fish for their own private use and to sell for profit? If there is a promising alternate species of fish that can be fished or a way of privately harvesting fish, what would be the best way to converse and educate these conclusions to the Filipino fishers? Hopefully, these findings can benefit the Filipinos by giving them a quicker, simpler, and more profitable way of fishing and earning money, that can improve the fishermen and their family’s way of life and preserve the manta rays.

 

The initial purpose of this project will be to research the primary reasons why manta rays are being hunted, besides the fact that the meat is a delicacy. But probably the main purpose will be to find alternative ways for fishing families to make the same amount of profit without hurting the manta ray or any other fish population. Research will be done, along with firsthand interview with the best diver throughout the whole of the Philippines and to learn for his knowledge about the situation. Also, if possible, interviews or survey will be done to Filipino fishermen who either hunt the manta rays or other types of fish. These findings will guide what I do throughout the rest of this project and will determine what kind of experiment I chose to do.

It is hoped that the exploitation of the manta rays will be decreased and even stopped, and to find a better and more profitable type of fish or way of fishing for the Filipino fishers.

 

 

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Biology

 

Common Names and Synonyms

 

Manta birostris is commonly called the manta ray. The first part of both its scientific and common name is manta, which in Spanish means “blanket”, and is a perfect description of the special spherical shape of the body. There are about eighteen different synonym names to the manta ray in English, and three of which are as follows: prince alfreds ray, blanketfish, and devil ray. A few other synonyms include manta atlantica (Spanish); oni-itomaki-ei (Japanese); jamanta (Portuguese); and salannga (tagalong).

 

Classification

 

 

Kingdom: Animalia (animals)

Phylum: Chordata (vertebrates, have notochord)

SubPhylum: Vertebrata (vertebrates)

Class: Chondrichthyes (cartilaginous fish)

Subclass: Elasmobranchii (sharks and rays)

Order: Myliobatiformes (rays)

Family: Myliobatidae (Eagle Rays),

Genus: Manta (blanket)

Species: birostris (Atlantic Mantas)

 

The taxonomy of the mantas are presently being explored and probed. Manta birostris, Manta ehrenbergii, and Manta raya are the three different species that have been, but the three are thought to be the same species. Manta ehrebergii and Manta raya are probably only isolated populations of manta rays, and were therefore given different names.

 

 

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Morphology and Physical Description

 

The manta rays are the largest known rays in the world, and have a special spherical body with a greater width than length. An average size, measured by width, of a manta is about 6.7 meters but can achieve a maximum width of about 9 meters. Although the average is 6.7 meters, the common sized manta rays seen are about 4 meters. They typically weight about 1200 kg to 1400 kg. Mantas have a life span of about 20-25 years, but many never reach this age because they are hunted by fishers. Manta rays have only two pectoral fins that give it its graceful and swift movements. They “fly” the water by basic flaps of its fins. They also have two cephalic lobes that extend in front of their wide, terminal mouths. They can be curled up while swimming, to prevent friction reducing the speed.

 

The manta rays have flat bodies and a spineless tail without a sharp end. They have smooth skin and five pairs of gills. They have about 18-20 rows of teeth, decreasing to 12-14 at the corners of the mouth, at the lower jaw. The colors are usually brown, grayish blue, or black, and some have different color patterns or pale patches. They have a pair of eyes on the two sides of the so-called flat head. The bodies of the manta rays have a thicker mucus coating to protect themselves than all the other known rays.

 

Internally, the bone structure of the mantas is relatively simple. The two sides, which look like wings, are made of Ceratotrichia (fin rays) and cover most of the ray. In the center there is a backbone called Vertebral Column, and in the center of the backbone the Basal Cartilages, Gill Bars, and Pectoral Gridle create something that looks like a chest. Radial Cartilage separates this “chest” from the Ceratotrichia. Also, the mantas have a skull called Chondrocranium that is connected to the Cephalic lobes. The internal organs include the following: Oesophagus, gills, heart, stomach, and etc. (See diagram below).

 

 

Additionally, they have filters that are made up of plates of pink-brown tissues that are in the rays’ mouth. These tissues span between the gill support structures. The reason he manta rays grow so big as they do is because they filter feed, which is the reason they are the biggest rays because other rays don’t filter feed.

 

 

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Getting Food

 

Manta rays are filter feeders, with occasional consumption of small fish, but are primary planktivores. They are also carnivores and eat non-insect arthropods. Mantas use their cephalic lobes to scup plankton filled water into their mouths and small fish. They filter the water that they suck in through the gills, and plats of pink-brown tissue in the mouths, spanning between the gills support structures, filter and trap all organisms in the water. Mantas feed in areas of water where there is a large concentration of their primary food, zooplankton, and areas like these there can even be 50 individual manta rays feeding. The teeth that are present in the mouths of the mantas remain unused and nonfunctional during feeding. The manta rays swim in vertical lops while feeding!

 

“They often slowly swim in vertical loops. Some researchers suggest this is done to keep the rays prey within the area while feeding.” (http://animaldiversity.ummz.umich.edu/site/accounts/information/Manta_birostris.html)

 

Reproduction

 

The reproduction of manta rays is a sexual reproduction, where multiple males court one female. A manta ray is sexually mature at the age of five, and the reproduction period spans from December to April. Large numbers of manta rays gather together, and the courting is done at a depth of 10-20 meters in rocky reefs in tropical waters. For 20-30 minutes males will follow the female closely at their tale at a faster speed than normal. When the female decreases her speed the male will bite one of her pectoral fins to grasp her. The male then positions his body under the females, inserts his clasper into the cloaca of the female, and inserts his sperm. The male rapidly swims away and another male comes to the female and repeats the same process. Usually after about two males the female swims away. The gestation period is 13 months long and is viviparous (pup develops inside the mother). After the gestation period the female gives birth to one or two live young manta rays. These new pups are about 1.1 to 1.4 meters long and are wrapped up in their pectoral fins right after birth

 

Environmental Factors

 

 

The manta rays live only in salt waters, close to shore, and in shallow waters. They can only be found in tropical waters and in warm temperate coastal regions with average temperatures ranging from 26 to 29 Celsius. Mantas live in shallow waters but can swim to a depth of 120 meters, although the actual depth is unknown.

 

There are many small parasites that use the manta rays as host. The exact parasites or diseases are unknown but it is known that the manta rays do have parasites living on them. To rid themselves from these parasites, along with dead skin on their bodies, they leap out of the waters to a height of seven feet and land with a crash. Also, the mantas go through something called a “cleaning stations” where wrasse fish swim around them picking off parasites and dead skin. Another symbiotic interaction that the manta rays have to rid themselves of parasites is with the remora fish. These fishes hitch rides with the mantas and feed on the parasites and on plankton of the mantas. Because of the manta ray’s size it has almost no natural predators, but sharks have been known to attack mantas. Other then the tough skin and great size the mantas have no defense mechanisms against predators.

 

The present environment of the manta rays, which includes overfishing and tropical regions with poor amounts of nutrients, decrease the population and number of living manta rays. In past years overfishing throughout the world was a big issue but is much less at present times. Manta rays, however, are still being hunted in the Philippines and so the amounts of mantas in the Philippines have been decreasing. Mantas are hunted with nets one kilometer long and 30 meters high, that not only catch mantas but also dolphins and endangered species of turtles. Mantas are known to swim at a usual depth that is above 30 meters and with nets one kilometer long mantas are easily catches and killed.

 

 

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Origin and Distribution

 

The origin of the Manta rays is unknown but it was first described by writing in 1798 by Dondroff. Although, the known dating of the manta rays goes all the way back to 100-800 A.D. These magnificent animals were worshiped by the people of ancient Peru called Moche. They often include mantas in their art. It is believed that the mantas evolved from bottom feeding ancestors. There is no known origin for manta rays in the Philippines because mantas are free swimmers and are not bound to certain areas. They are distributed from 35 degrees north to 35 degrees south. They live only in warm waters with average temperatures from 26 to 29 Celsius in tropical and warm temperate coastal regions.

 

 

 

Importance to People

 

 

Formerly, the manta rays were harvested commercially in California and Australia. Licensed manta ray fishers use 30 meters high, one kilometer long nets to catch these animals, which also catch other species like dolphins and endanger turtles.  They were harvested for the liver oil and the skin used in abrasive. The mantas are presently not hunted in great quantities worldwide, but are hunted in the Philippines. The meat of the manta is considered a delicacy. Although, the mantas have been used for oil, abrasive, and presently as a delicacy, the major importance of these animals to humans is in tourism. Diving industries for tourism are created as more and more people want to swim and see these well-known creatures. Many times mantas will advance and seek attention from divers, as they might enjoy bubbles and contact by humans. Ecotourism is when humans benefits on nature and is an important way for the Philippines to earn money. The economy of the Philippines depends of tourism and ecotourism depends on certain aspects of nature. For diving coral and marine life are the aspects that pull people to dive in the Philippines. By killing one spectacular marine animal, that many come to see individually, tourism levels might decrease.  It might hurt the Filipino economy by eliminating such a magnificent and attractive creature like the manta rays.

 

Survivability and Endangered Status

 

Manta rays are categorized as “Near Threatened” by the World Conservation Union (IUCN). Due to the hunting of mantas in the Philippines for the meat, the number of mantas in the Philippines has been decreasing. In 1998 the Philippines banned any hunting or selling of manta rays, with a four year imprisonment or fine to any offenders. But in 2002 the ban was lifted due to misguided political pressure. In 2002, Jose Ma. Lorenzo Tan, President of WWF Philippines, said “Today, all the large marine creatures in the Philippines, without exception, are under threat” (http://www.mantas.org/index.php?name=News&file=article&sid=30). This shows the status of the manta rays and other large creatures, and demonstrates the importance of a natural balance. Large marine animals need to live free of endangerment by hunting to a certain extent so their population will not be in a steady decrease.

 

 

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Potential Solutions

 

Obviously, the exploitation of the manta rays is something that is not neither good nor beneficial. If actions and preventions are not taken this species might go extinct, and will that result in a major hole in the food chain? Could extinction of the manta ray create a future problem throughout different parts of the ecosystem? The manta ray is a species that is near threatened and have a fragile population due to the slow reproduction rate. A further understanding and study must be taken to find the potential damage that the extinction of the manta ray can create, especially in the Philippines were they are hunted and killed more than other countries. Hopefully, the manta rays can be preserved and can be given the chance to flourish in the Philippines, which it could have done if it was not hunted. A manta ray have many different cash parts where soft, plump meats is Php90 per kilo, gill rakers is Php500 per kilo, and in one source it said that a fin can even be about Php8380 (US$200). An average manta is about 1200 to 1400 kilogram, and all this weight is distributed between mostly meat, some gill rakers (a manta has only five gills), and the two big fins. One manta is an extremely profitable animal to hunt, but are hunted in too great of number. Big fishing nets are used to catch and hunt these rays but the whole process is tiresome and hard. One manta usually weights more than 1000 kg so it is a heavy job to catch and butchered them. For a single family one catch gives good profit and so to prevent hunting of these animals another, also profitable, fishing source must be found. Below are three possible alternative sources of money that will hopefully seem attractive to Filipino fishermen and can make their life easier. Each possibility will be analyzed with advantages and disadvantages to give a full overview of the possibility. 

 

Possibility 1 - MILKFISH CULTIVATION (Example fish type cultivation)

 

Milkfish is a natural fish in the Philippines and have therefore been harvested for about 400 years. So instead of a constant hunt for manta rays, which may not be seen in constant intervals, there is the possibility of fish production. One species of fish that seems to be profitable is the milkfish, which is commonly harvested in the Philippines, along with Taiwan and Indonesia. Would cultivating milkfish bring enough profit to a simple fishing family?

 

Chart of milkfish (Marketing Margins for Last Purchase/Receipt and Sale for 114 Milkfish Dealers, the Philippines, 1974):

 

Item Pesos per Kilo Percentage of retail price
Luzon Visayas Mindanao Luzon Visayas Mindanao
Farm gate price 3.63 3.19 3.46 64 70 66
Producer's marketing cost 0.19 0.20 0.16 3 4 3
Producer's selling price 3.82 3.39 3.62 67 74 69
Intermediaries between producers and retailers:  
Marketing cost 0.24 0.13 0.08 4 3 1
Gaina 1.05 0.26 1.05 19 5 20
Retailers:            
Marketing cost 0.23 0.35 0.20 4 8 4
Gaina 0.33 0.45 0.30 6 10 6
Retail price 5.67 4.58 5.25 100 100 100
Marketing margin 2.04 1.39 1.79      

 

Advantages:

1. The milkfish is a highly tolerant species, herbivore, and have a good growth rate (300+ kg in one season). Within the Philippines there is a well established market for Milkfish, which makes it easy to sell. The milkfish can grow up to 1.5 meters and weigh up to 15 kg. It is sexually mature at 5 kg (5-6 years) and can lay 1-9 million eggs a season.

2. The unit price of the milkfish has been constantly increasing and is now averaging about Php84 (US$2) per kg. The consumers in the Philippines have demonstrated to buy a certain amount or quantity despite the increasing price.

      a. Average weight graph of milkfish:

 

Average weight (grams) P/piece P/kg
333 2.03 6.10
250 1.65 6.60
200 1.65 8.25
167 1.27 7.60
143 1.17 8.18
125 1.02 8.16

 

3. Strengths Chart:

a. Low production cost:

i. cheap fry;

ii. low in food chain – planktivore/herbivore/detritivore;

iii. good response to fertilizer (fertilizer increase greatly the yielding)

iv. good growth rate.

b. Well established local/national food fish markets – price premium compared with other local species (in Taiwan and Philippines);

c. Attractive appearance;

d.  Low input, low risk

(http://209.85.175.104/search?q=cache:mC1SVH_IjyYJ:www.aqua-information.ait.ac.th/aarmpage/pdf/hambrey_2000-coastal_aquaculture/03-milkfish.pdf+milkfish+price&hl=no&ct=clnk&cd=14)

 

Disadvantages:

1. Weakness Chart:

a. variable fry supply;

b. relatively low market value;

c. no high value international markets;

d. intramuscular bones;

e. susceptibility of pond growout to cyclone - low salinity causes reduced algal production;

f. high costs of hatchery production

(http://209.85.175.104/search?q=cache:mC1SVH_IjyYJ:www.aqua-information.ait.ac.th/aarmpage/pdf/hambrey_2000-coastal_aquaculture/03-milkfish.pdf+milkfish+price&hl=no&ct=clnk&cd=14)

2. Obviously, there are much more organization and planning that needs to be done within fish cultivation. Gates, food, and rental of the place is just three of all the necessities that cost money and are required to be able to have a fish harvesting farm. Supplies and items cost much more to run a fish production rather than a simple harpoon or net hunt of manta rays.

3. The cheapest way to grow milkfish is to convert a patch of mangrove swamp into a grow out pool. The second cheapest way would be to grow them in vast or inland pools, but both of these methods, which are the two cheapest, require a lot of money. Money is the one thing that fishermen don’t have good amounts of, and that makes fish cultivation very hard and virtually impossible.

 

 

 

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Possibility 2 - PHLIPPINE TUNA BUSINESS

 

Hunting manta rays does not give a constant and secure income to a family, although the profit of a manta is high. Throughout the Philippines there are many different species of fish that are highly fished for export and tuna is one type of fish. General Santos City is the tuna capital of the Philippines and tuna business generates about 120,000 jobs. Also, the tuna business in the Philippines generates jobs for fishermen with supplying fiberglass boats. Tuna business is well used and generates many types of work.

 

Advantages:

1. Fishing for manta rays gives a family no constant and safe income and only men can work. But with the tuna business both men and women can find a job at the tuna industry. Both men and women can clean fish and be canneries and Asian canneries get about US$ 0.66 an hour of work and each day is eight hours. This equals about US$ 5.28 a day, which is PhP 221.

2. Due to the shortage of wood in making pumpboats, President Gloria and the Cabinet has ordered to build 100 long line fiberglass boats for fishing that generates 2,000 jobs. The fishermen will repay the payments of the boat out of the profit of their catch. This might make these fishermen into business owners, which is actually one of the goals of President Gloria within this project.

 

 

Disadvantages:

1.  Global warming and El Nino has been reducing the tuna catches greatly. Less and less tuna is being catches which means that more and more people has to leave the industry. Usually a normal person could average about US$ 5 a day, but due to the loss of tuna the payment is now down to about US$ 4 a day. It is harder to find and keep jobs. Also, the tuna industry used to be a 24-hour working place but now it is cut down to only eight hours a day because of less tuna is caught.

2. Travel might obviously be a big disadvantage. One woman travels about 10 kilometer a day where she wakes up at three in the morning and arrives at five. The job is a first-come-first-serve basis, so to be able to get a job for the day you need to arrive early.

3. Since less and less tuna is found it might be hard for fiberglass fishermen to catch enough each day to repay the payments of the boats. Although the price required might be reduced, it will take them longer to pay off their depth and therefore it will take longer before they can become independent and get a 100 percent profit on their catch. It might be possible that the payment required is not reduced and so the family will get less income which might send a family deeper into depth.

 

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Possibility 3 - ECOTOURISM

 

Many of the ideas and solutions that can be brainstormed might be good, but the truth is that most have a little chance of working. All ideas might be great solutions but in this country the chance of success is small just because of a basic lack of money. Most fishermen are far below the poverty line and have no chance of being able to change from a fishing life. The most qualified and accomplishable solution would be ecotourism. These solutions are primary targeted to fishermen who hunt manta rays, because my whole project is on the manta ray. So a man who hunts manta rays for a living will, obviously, knows where the ideal spots for manta rays are. They also would probably have a boat, so with these two factors they already have a possibility of starting with ecotourism. They have multiple options of which they can choose, for example they could partner with an existing tourist center like a hotel or agency. They have the freedom of starting fresh and make their own business. Obviously, ecotourism can be started up anywhere that would or can draw tourists. There are many possible locations where manta rays can be used to draw tourists, but one certain place that provides even more than mantas is Ticao. While interviewing a Filipino that deals with ecotourism I found that hunting manta rays is a very risky job. Fishermen use compressors to dive straight down then straight up without equalizing, and that often results with the fisherman becoming paralyzed for life or dies. It puts a lot of strain on the fishermen and their life is under a constant threat.

 

Advantages:

1. Ticao is one of many islands that are a relatively undisturbed and none commercialized, without many resorts. If fishermen could start something on a island like that, there would not be extreme competition. They would be able to determine the prices and tourist would use their place without much else to be offered. The Major of Monreal town, one of the four municipalities within the island of Ticao, said “This is not an ambitious aspiration. In fact, we do not even intend to modernize our place to be attractive to tourists. What brings them here is the natural beauty of our island and, of course, the fabulous manta ray” (http://www.businessmirror.com.ph/05092007/economy05.html). This source tells us that there is no intention to modernize the place, which poor fishermen families could not even dream about trying and that the natural beauty draws tourist, which is what the families depend solemnly on for tourist. For poor fishermen these factors are perfect for starting and developing an ecotourism center.

2. This solution gives the fishermen an increased freedom of how they would want to operate.  They could partner together with other fishermen and share boats, and together they could buy equipment and build a small building for their business. Profit will be much more secure and sustainable once the business is operating rather than illegal hunting of manta rays that may prove to be inconsistent. Places like Ticao, provide a market of a constant increase of tourists that provide greater profit. With greater profit comes better business then even more profit.

3. For a fisherman, manta ray hunting puts extreme pressure and tension on a body. With ecotourism the bodies of the fishermen are much more relaxed and in better health. With ecotourism a work day can be about 12 hours a day or less, but with manta fishing there are very many dives and work day exceeds 12 hours.

4. Ecotourism is most importantly easy money. A fisherman gets a constant salary and gets easy earned money from tourists. With Jet Ski maintenance and fuel is everything that needs to be provided. With only these factors that require money, a great and easy profit is earned.

 

Disadvantages:

1. Places like the Ticao might have natural disadvantages. In Ticao when waters are still, usually from December to May, manta rays will fill the natural bowl. The rest of the year water currents and waves are too strong to be able to dive in. The currents in the bowl create a deadly whirlpool that makes diving much too dangerous. This is a factor that is an extreme disadvantage because half the year there will not be a lot of tourists throughout the area. This requires the fishermen to find altnerative sources for money like fishing and seaweed harvest.

2. For people to want to come and be able to come, good transportation methods are required. If the island is already modernized then transportation will probably be already be set. But the disadvantage comes to places that are not yet modernized, so therefore transportation would have to be fixed. Transportation means require money that most fishermen don’t have.

 

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Bibliography

 

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 “Tuna industry players seek access with Pacific nations”. Sun.Star Davao. 12 September 2006. 27 April 2008 <http://www.sunstar.com.ph/static/dav/2006/09/12/bus/tuna.industry.players.seek.access.with.pacific.nations.html>.

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