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Rare & Wonderful

Studying the charismatic white spotted eagle ray populations of South Caicos.
Story & Photos By Jan Lupton
Venture on a dive or snorkel in the beautiful seas surrounding the Turks & Caicos Islands and you may be treated to an encounter with one or more white spotted eagle rays gracefully flying through the water. In contrast to the southern stingray, another ray species commonly found in TCI waters, white spotted eagle rays (Aetobatus narinari) are distinguished by the beautiful and intricate patterns covering their dorsal surface. They are passive creatures and although they have venomous stings on their tails, they are never aggressive unless under attack; although quite shy they are not too wary of divers and will often pass right next to you.
There are very few places in the world where you may be privileged enough to see eagle rays schooling in such large numbers and in such accessible locations as in the TCI. For this reason, the populations here are truly unique and special. They also remain a mystery to scientists with very little documentation available about their life histories or behaviors.
What do we know?
Information we do have about this animal mainly comes from observations of captive individuals kept on display in public aquariums and a handful of scientific observations in the wild. Until recently it was believed that the same species was globally distributed around the worlds’ tropical and sub-tropical seas. However, genetic analysis has now revealed that this is more of a species complex (i.e. there is more than one form within the species) as populations in the Central Atlantic and Caribbean are distinct from those found in the Western Pacific.
Although white spotted eagle rays are commonly seen out at sea and around the wall drop-offs, they also venture into shallower lagoons and seagrass beds to feed. With a row of plate-like teeth, they are well adapted for crushing shelled animals such as crabs, oysters, clams and juvenile conch for which they forage on sandy bottoms. They may also feed on small fish and even octopus. The great hammerhead (Sphyrna mokarran) is one of the main predators of eagle rays in Turks & Caicos. It is suggested that pursuit by one of these large sharks is the reason you may witness an eagle ray leaping high into the air in its attempt to escape.
Males will mate with more than one female over a mating season, reported to be during periods of warmer water temperatures in the summer months. Courtship behavior includes the male continuously following and aggravating a female, often inflicting bite marks to her fins and dorsal surface. If he succeeds, the pair will then mate with their ventral sides together. Males have reproductive organs called claspers which can be seen, when viewed from above, protruding from under the pelvic fins on either side of the tail base.
The gestation period for the female is believed to be about a year and then she will give birth to up to four young. Eagle rays are ovoviviparous which means that the eggs develop and hatch inside the mother and the embryos are then nourished from a yolk sac. The young are fully formed at birth and are around 30 cm wide. There have been a handful of successful breeding programs of this species in captivity but witnessing birthing in the wild is extremely rare. There have been a few documented accounts of newborn eagle rays from estuarine areas around the world, but very little information from the Caribbean.
Previous research on populations
More than 10 years ago, scientists at Bimini Biological Field Station, Bahamas carried out an extensive study (the first of its kind) of the eagle ray populations around the island. They identified 157 individuals by photographs and attached ultrasonic transmitters to 17 individuals which they were then able to track. They recorded schools of up to 60 eagle rays which were independent of gender or size. Mating or courtship activity was never observed and so it was suggested that the schools were either formed for protection against predators or for some other kind of unknown social interaction.
They also found that eagle rays in Bimini exhibited both high site fidelity (i.e. the same individuals lived in the same areas) and daily movement patterns that coincided with the tidal cycle. They were also only seasonal residents because they left the island during the summer months only to return again in the fall. Their findings were groundbreaking but also generated a host of other questions. Eagle rays are known to have the largest brain to body size ratio of any fish, they are social animals and unlocking the secrets of their interactions and their day to day habits was the aim of a study I set up in early 2009 at the School for Field Studies in South Caicos.
“Fingerprinting” eagle rays in South Caicos
The markings found on an eagle ray’s back are entirely unique to that particular individual. Every squiggle, circle, line and spot goes into the formation of a distinct pattern that can be used to distinguish one eagle ray from another. Scientists often use artificial tags to recognize and monitor individual animals in a population. Although useful for certain research, this method is often expensive, invasive and may cause stress and damage to the animal. Eagle rays lend themselves ideally to the use of photography to identify individuals from their natural markings, which is far less invasive and is also a less expensive way of collecting data on their movements and social interactions.
Since April 2009, photographs have been collected of eagle rays taken on dive and snorkel trips in South Caicos, and in particular around Long Cay where they enter the East Harbour lagoon from the open waters of the Columbus Passage. Between April and September 2009, 82 different individuals were identified, approximately 60% of which were females and 40% males. Specialized pattern matching computer software called I3S (see www.reijns.com/i3s), which is currently applied around the world in research on manta rays and whale sharks, was adapted to use on photographs of eagle rays. Three reference points on the pelvic fin of an unknown individual are selected and every marking within these points is then drawn around. This outlined pattern of the markings (or “fingerprint”) is then matched to a database of patterns from known individuals. This has successfully allowed the identification process to be much quicker and is the first time such a technique has been applied to studies of this species.
This project is in its very early stages but already we have some interesting findings. It seems that, like the populations in Bimini, eagle rays here also display high site fidelity with the same individuals consistently being identified at the same locations. Over 20 individual eagle rays have been seen more than three times and although there are many repeat sightings, there are still new individuals being identified almost every week. Around 60% of sightings are of two or more eagle rays swimming together and these groups are more often made up of either a mix of sexes or all females. Groups made up entirely of males are less common to see. In contrast to the findings from Bimini, sightings of eagle rays here are continuous throughout the year and courtship and mating behavior has been witnessed over the summer including an increase in the presence of mating scars on females. Interestingly, there are a handful of individuals that have been seen regularly at the same sites for over five months but others seem to be sighted regularly for a couple of weeks and then disappear. Is it possible that some eagle rays are transient visitors to these areas and some are permanent residents? Another interesting aspect of their social behavior is the associations they have with other individuals. Are certain eagle rays more likely to group and interact together than others or are these purely random assemblages?
There are still many questions to be answered but more information and further research about these populations will hopefully help lead to a better understanding about the lives of these mysterious creatures. Due to their low reproductive output and the susceptibility of their near shore habitats to fishing, white spotted eagle rays are currently classed globally as “Near Threatened” by the International Union for Conservation of Nature (IUCN). This means they are likely to become endangered in the future. Scientific research to gain insights into their movement patterns and life histories is therefore all the more important in order to support decisions about their management and conservation worldwide.
This project has recently been extended to study the spotted eagle ray populations around Providenciales, with coordination by Jackie Walker of Big Blue Unlimited. We aim to collect as many images of individuals as possible in order to build up a database of sightings from around the Islands. We would be grateful for any details of encounters and photographs would be much appreciated. Please send to jackie.t.walker@gmail.com (Provo) or janlupton@hotmail.com (South Caicos). For more information about this research and to access the sightings database, see www.spottedeaglerays.com.

Studying the charismatic white spotted eagle ray populations of South Caicos.

Story & Photos By Jan Lupton

White spotted eagle rays in Turks & Caicos waters

White spotted eagle rays in Turks & Caicos waters

Venture on a dive or snorkel in the beautiful seas surrounding the Turks & Caicos Islands and you may be treated to an encounter with one or more white spotted eagle rays gracefully flying through the water. In contrast to the southern stingray, another ray species commonly found in TCI waters, white spotted eagle rays (Aetobatus narinari) are distinguished by the beautiful and intricate patterns covering their dorsal surface. They are passive creatures and although they have venomous stings on their tails, they are never aggressive unless under attack; although quite shy they are not too wary of divers and will often pass right next to you.

There are very few places in the world where you may be privileged enough to see eagle rays schooling in such large numbers and in such accessible locations as in the TCI. For this reason, the populations here are truly unique and special. They also remain a mystery to scientists with very little documentation available about their life histories or behaviors.

What do we know?

Information we do have about this animal mainly comes from observations of captive individuals kept on display in public aquariums and a handful of scientific observations in the wild. Until recently it was believed that the same species was globally distributed around the worlds’ tropical and sub-tropical seas. However, genetic analysis has now revealed that this is more of a species complex (i.e. there is more than one form within the species) as populations in the Central Atlantic and Caribbean are distinct from those found in the Western Pacific.

Although white spotted eagle rays are commonly seen out at sea and around the wall drop-offs, they also venture into shallower lagoons and seagrass beds to feed. With a row of plate-like teeth, they are well adapted for crushing shelled animals such as crabs, oysters, clams and juvenile conch for which they forage on sandy bottoms. They may also feed on small fish and even octopus. The great hammerhead (Sphyrna mokarran) is one of the main predators of eagle rays in Turks & Caicos. It is suggested that pursuit by one of these large sharks is the reason you may witness an eagle ray leaping high into the air in its attempt to escape.

Males will mate with more than one female over a mating season, reported to be during periods of warmer water temperatures in the summer months. Courtship behavior includes the male continuously following and aggravating a female, often inflicting bite marks to her fins and dorsal surface. If he succeeds, the pair will then mate with their ventral sides together. Males have reproductive organs called claspers which can be seen, when viewed from above, protruding from under the pelvic fins on either side of the tail base.

The gestation period for the female is believed to be about a year and then she will give birth to up to four young. Eagle rays are ovoviviparous which means that the eggs develop and hatch inside the mother and the embryos are then nourished from a yolk sac. The young are fully formed at birth and are around 30 cm wide. There have been a handful of successful breeding programs of this species in captivity but witnessing birthing in the wild is extremely rare. There have been a few documented accounts of newborn eagle rays from estuarine areas around the world, but very little information from the Caribbean.

Previous research on populations

More than 10 years ago, scientists at Bimini Biological Field Station, Bahamas carried out an extensive study (the first of its kind) of the eagle ray populations around the island. They identified 157 individuals by photographs and attached ultrasonic transmitters to 17 individuals which they were then able to track. They recorded schools of up to 60 eagle rays which were independent of gender or size. Mating or courtship activity was never observed and so it was suggested that the schools were either formed for protection against predators or for some other kind of unknown social interaction.

They also found that eagle rays in Bimini exhibited both high site fidelity (i.e. the same individuals lived in the same areas) and daily movement patterns that coincided with the tidal cycle. They were also only seasonal residents because they left the island during the summer months only to return again in the fall. Their findings were groundbreaking but also generated a host of other questions. Eagle rays are known to have the largest brain to body size ratio of any fish, they are social animals and unlocking the secrets of their interactions and their day to day habits was the aim of a study I set up in early 2009 at the School for Field Studies in South Caicos.

“Fingerprinting” eagle rays in South Caicos

School of Eagle Rays

School of Eagle Rays

The markings found on an eagle ray’s back are entirely unique to that particular individual. Every squiggle, circle, line and spot goes into the formation of a distinct pattern that can be used to distinguish one eagle ray from another. Scientists often use artificial tags to recognize and monitor individual animals in a population. Although useful for certain research, this method is often expensive, invasive and may cause stress and damage to the animal. Eagle rays lend themselves ideally to the use of photography to identify individuals from their natural markings, which is far less invasive and is also a less expensive way of collecting data on their movements and social interactions.

Since April 2009, photographs have been collected of eagle rays taken on dive and snorkel trips in South Caicos, and in particular around Long Cay where they enter the East Harbour lagoon from the open waters of the Columbus Passage. Between April and September 2009, 82 different individuals were identified, approximately 60% of which were females and 40% males. Specialized pattern matching computer software called I3S (see www.reijns.com/i3s), which is currently applied around the world in research on manta rays and whale sharks, was adapted to use on photographs of eagle rays. Three reference points on the pelvic fin of an unknown individual are selected and every marking within these points is then drawn around. This outlined pattern of the markings (or “fingerprint”) is then matched to a database of patterns from known individuals. This has successfully allowed the identification process to be much quicker and is the first time such a technique has been applied to studies of this species.

This project is in its very early stages but already we have some interesting findings. It seems that, like the populations in Bimini, eagle rays here also display high site fidelity with the same individuals consistently being identified at the same locations. Over 20 individual eagle rays have been seen more than three times and although there are many repeat sightings, there are still new individuals being identified almost every week. Around 60% of sightings are of two or more eagle rays swimming together and these groups are more often made up of either a mix of sexes or all females. Groups made up entirely of males are less common to see. In contrast to the findings from Bimini, sightings of eagle rays here are continuous throughout the year and courtship and mating behavior has been witnessed over the summer including an increase in the presence of mating scars on females. Interestingly, there are a handful of individuals that have been seen regularly at the same sites for over five months but others seem to be sighted regularly for a couple of weeks and then disappear. Is it possible that some eagle rays are transient visitors to these areas and some are permanent residents? Another interesting aspect of their social behavior is the associations they have with other individuals. Are certain eagle rays more likely to group and interact together than others or are these purely random assemblages?

There are still many questions to be answered but more information and further research about these populations will hopefully help lead to a better understanding about the lives of these mysterious creatures. Due to their low reproductive output and the susceptibility of their near shore habitats to fishing, white spotted eagle rays are currently classed globally as “Near Threatened” by the International Union for Conservation of Nature (IUCN). This means they are likely to become endangered in the future. Scientific research to gain insights into their movement patterns and life histories is therefore all the more important in order to support decisions about their management and conservation worldwide.

This project has recently been extended to study the spotted eagle ray populations around Providenciales, with coordination by Jackie Walker of Big Blue Unlimited. We aim to collect as many images of individuals as possible in order to build up a database of sightings from around the Islands. We would be grateful for any details of encounters and photographs would be much appreciated. Please send to jackie.t.walker@gmail.com (Provo) or janlupton@hotmail.com (South Caicos). For more information about this research and to access the sightings database, see www.spottedeaglerays.com.



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