This guide is intended to assist fishery observers in the visual identification of giant manta rays…
Giant Manta Ray
About The Species
The giant manta ray is the world’s largest ray with a wingspan of up to 29 feet. They are filter feeders and eat large quantities of zooplankton. Giant manta rays are slow-growing, migratory animals with small, highly fragmented populations that are sparsely distributed across the world.
The main threat to the giant manta ray is commercial fishing, with the species both targeted and caught as bycatch in a number of global fisheries throughout its range. Manta rays are particularly valued for their gill rakers, which are traded internationally. In 2018, NOAA Fisheries listed the species as threatened under the Endangered Species Act.
Information on the global distribution of giant manta rays and their population sizes is lacking. Regional population sizes are small, ranging from around 100 to 1,500 individuals, and in areas subject to fishing, have significantly declined. Ecuador is thought to be home to the largest population of giant manta ray, with large aggregation sites within the waters of the Machalilla National Park and the Galapagos Marine Reserve. Overall, given their life history traits, particularly their low reproductive output, giant manta ray populations are inherently vulnerable to depletions, with low likelihood of recovery. Additional research is needed to better understand the population structure and global distribution of the giant manta ray.
- Throughout Its Range
CITES Appendix II
- Throughout Its Range
Manta rays are recognized by their large diamond-shaped body with elongated wing-like pectoral fins, ventrally placed gill slits, laterally placed eyes, and wide terminal mouths. In front of the mouth, they have two structures called cephalic lobes which extend and help to introduce water into the mouth for feeding activities (making them the only vertebrate animals with three paired appendages).
Manta rays come in two distinct color types: chevron (mostly black back and white belly) and black (almost completely black on both sides). They also have distinct spot patterns on their bellies that can be used to identify individuals. There are two species of manta rays: giant manta rays (Manta birostris) and reef manta rays (Manta alfredi). Giant manta rays are generally larger than reef manta rays, have a caudal thorn, and rough skin appearance. They can also be distinguished from reef manta rays by their coloration.
Behavior and Diet
The giant manta ray is a migratory species, and seasonal visitor along productive coastlines with regular upwelling, in oceanic island groups, and near offshore pinnacles and seamounts. The timing of these visits varies by region and seems to correspond with the movement of zooplankton, current circulation and tidal patterns, seasonal upwelling, seawater temperature, and possibly mating behavior.
Although the giant manta ray tends to be solitary, they aggregate at cleaning sites and to feed and mate. Manta rays primarily feed on planktonic organisms such as euphausiids, copepods, mysids, decapod larvae and shrimp, but some studies have noted their consumption of small and moderately sized fishes as well. When feeding, mantas hold their cephalic fins in an “O” shape and open their mouths wide, creating a funnel that pushes water and prey through their mouth and over their gill rakers. Manta rays use many different types of feeding strategies, such as barrel rolling (doing somersaults over and over again) and creating feeding chains with other mantas to maximize prey intake.
Giant manta rays also appear to exhibit a high degree of plasticity in terms of their use of depths within their habitat. During feeding, giant manta rays may be found aggregating in shallow waters at depths less than 10 meters. However, tagging studies have also shown that the species conducts dives of up to 200 to 450 meters and is capable of diving to depths exceeding 1,000 meters. This diving behavior may be influenced by season and shifts in prey location associated with the thermocline.
Where They Live
The giant manta ray is found worldwide in tropical, subtropical, and temperate bodies of water and is commonly found offshore, in oceanic waters, and near productive coastlines. As such, giant manta rays can be found in cool water, as low as 19°C, although temperature preference appears to vary by region. For example, off the U.S. East Coast, giant manta rays are commonly found in waters from 19 to 22°C, whereas those off the Yucatan peninsula and Indonesia are commonly found in waters between 25 to 30°C. The species has also been observed in estuarine waters near oceanic inlets, with use of these waters as potential nursery grounds.
Lifespan & Reproduction
Manta rays have among the lowest fecundity of all elasmobranchs (a subclass of cartilaginous fish), typically giving birth to only one pup every two to three years. Gestation is thought to last last around a year. Although manta rays have been reported to live at least 40 years, not much is known about their growth and development.
Commercial and Artisanal Fishing
The most significant threat to the giant manta ray is overutilization for commercial purposes. Giant manta rays are both targeted and caught as bycatch in a number of global fisheries throughout their range, and are most susceptible to industrial purse-seine and artisanal gillnet fisheries.
Efforts to address overutilization of the species through current regulatory measures are inadequate, as targeted fishing of the species still occurs despite prohibitions in a significant portion of the species’ range. Also, measures to address bycatch of the species in industrial fisheries are rare.
Harvest for International Trade
Demand for the gills of manta and other mobula rays has risen dramatically in Asian markets. With this expansion of the international gill raker market and increasing demand for manta ray products, estimated harvest of giant manta rays, particularly in many portions of the Indo-Pacific, frequently exceeds numbers of identified individuals in those areas and are accompanied by observed declines in sightings and landings of the species of up to 95 percent.
The giant manta ray is listed as threatened under the Endangered Species Act.
In addition, all manta rays are listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora.
At the 2013 meeting of the Conference of the Parties to the Convention on International Trade in Endangered Species of Wild Fauna and Flora, the Parties agreed to include all manta rays (Manta spp.) in Appendix II of CITES, with the listing going into effect on September 14, 2014. The inclusion of manta rays in CITES Appendix II will help ensure that the international trade in these species is legal and sustainable.
The U.S. Fish and Wildlife Service is the government agency designated under the ESA to carry out the provisions of CITES. NOAA Fisheries provides guidance and scientific support on marine issues given our technical expertise.
Key Actions and Documents
NOAA Fisheries and our partners conduct various research activities on the biology, behavior, and ecology of the giant manta ray. Some of our partners include federal agencies, nonprofits, and international organizations. The results of this research are used to inform management decisions and enhance our understanding of this threatened species.
Scientists are using the most recent technology to track the movements of giant manta rays. In June and July 2019, researchers with NOAA Fisheries and the Marine Megafauna Foundation collaborated to place satellite tags on manta rays in south Florida. The team successfully tagged five juvenile manta rays (one female and four males) and the tags are programmed to stay on for six months. The tags are very carefully attached by scientist using techniques that are as minimally invasive as possible. Our satellite tag, on a manta named Leo, has been providing us data for over a month.
A team of scientists recently completed a 3-day research cruise in the Flower Garden Banks National Marine Sanctuary in the Gulf of Mexico. The team conducted more than 20 dives throughout the sanctuary in an effort to find and tag a giant manta ray. The information provided by this satellite tagging efforts will help us determine the distribution of depth and temperature used by mantas, as well as evaluate residency and movement patterns.
Scientists are also using a special kind of satellite tag to assess survivorship of giant manta rays after being caught in artisanal gillnet fisheries. Results from this research can be used to develop standards for manta ray bycatch reduction and safe release practices, and inform management measures at a national and international level.
Small tissue samples are collected during tagging or capture for genetic analysis. Genetics are useful in understanding population structure, diversity within the population, and genetic exchange between populations. For example, we are collecting genetic samples to help us determine whether there is movement and genetic exchange among giant manta rays along the U.S. east coast and in the Gulf of Mexico. Tissue samples are less than 0.5 oz and collected by scientist using non-invasive methods.
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